the science behind the goodness in real tea, Camellia sinensis, nature’s healing herb
PROF. TISSA AMARAKOON and HEALTH
“The first bowl moistens my lips and throat. The second bowl banishes my loneliness and melancholy.
The third bowl penetrates my withered entrails, finding nothing except a literary core of five thousand scrolls.
The fourth bowl raises a light perspiration, casting life’s inequities out through my pores.
The fifth bowl purifies my flesh and bones.
The sixth bowl makes me one with the immortal, feathered spirits.
The seventh bowl I need not drink, feeling only a pure wind rushing beneath my wings.” “Song of Tea” Lu T’ung - 780 AD
and HEALTH TEA
your
the science behind the goodness in real tea, Camellia sinensis, nature’s healing herb
Edited by
Anura Gunasekera, Daya Wickramatunge & Dr. Anudini Liyanage
PROF. TISSA AMARAKOON
TEA & YOUR HEALTH
All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any information storage and retrieval system, without permission in writing from the publishers
Published by Dilmah Ceylon Tea Co. PLC. 111 Negombo Road, Peliyagoda , Sri Lanka www.dilmahtea.com
ISBN 978-955-0081-26-4
Tea is one of nature’s finest gifts to humankind. The story of its origins, attributed to a serendipitous discovery by the Chinese Emperor Shennong in 2737BC, is both romantic and deeply significant because since then, drinking tea has been known to be beneficial to human health in ways that are especially relevant to our lifestyles today, nearly 5,000 years later. In ancient times tea was harvested by physicians for its therapeutic value and poets and philosophers extolled the virtues of the herb.
It has always been my conviction that tea has no parallel in the botanical world. The infinite variety of tastes, shapes, textures, colours and aromas in tea that is made in the traditional, orthodox style can indulge every taste preference and every mood while delivering compelling health benefits. At a time when humankind is gaining fresh appreciation of the importance of nature, tea is unique in its elegant expression of the influence of soil, sunshine, wind, rainfall and temperature through the terroir that defines each batch of tea. I devoted my life to tea and carry this message
to every tea drinker: there is no beverage that is quite like tea. Fresh tea is rich in natural antioxidants and when made in the traditional, orthodox style - the only way to make good tea - it is both uniquely healthy and deliciously pleasing.
As we celebrate 150 years of Ceylon Tea and approach the 30th anniversary of Dilmah Tea, I reaffirm my commitment to nature’s healing herb – both in sharing the pleasure in real tea and in sharing the benefits of my life in tea through the philosophy - of making business a matter of human service.
There is no beverage in existence that can offer the same combination of pleasure and therapeutic effect as tea. The world is experiencing a renaissance in tea as a new generation discovers that tea is naturally good for human health and in this book, we hope to convey the extent of that goodness. Supported by a wealth of technical and anecdotal detail and compiled with great dedication by Prof. Tissa Amarakoon, ‘Tea & Your Health’ aims to dispel the myth and explain the scientifically proven health benefits in tea.
I thank all those who were involved in its production and take great pleasure in offering this book to the tea-drinking world. It is my prayer that every reader will benefit from knowledge of the natural goodness in tea.
Merrill J. Fernando, Founder of Dilmah Tea
History of Tea and its Medicinal Properties
The tea plant (Camellia sinensis), was found to grow naturally in tropical South East Asia, includes parts of China, India, Myanmar, Cambodia and Thailand. The Tea drinking habit and the cultivation of tea originated in China around the 6th century A.D, gradually spreading to neighbouring countries, including Japan. European traders, firstly the Dutch, introduced tea to Europe on a small commercial scale in the 17th century and, thereafter, to other countries. At the beginning, in China and in the other countries to which it was introduced, tea was considered as a medicinal drink.
By the 19th century the Dutch had started cultivation of tea in Java and Sumatra. Later, the British established more successful cultivations in India and notably in Ceylon (Sri Lanka), enabling the British to emerge as the leading tea trader in the world. By the beginning of the 20th century tea had become the most widely-consumed beverage in the world, next to water. By this time medicinal properties of tea were mostly forgotten and it was consumed regularly as a pleasant beverage. In the 1980s there was a renewed interest in the medicinal properties of tea, due to the emergence of results from modern scientific research on tea. Consumers all over the world now view tea in the context of its proven health beneficial properties.
Origin and Nomenclature of Tea
Before organised cultivation started, the tea plant was naturally found in the tropical forests of South East Asia, which include Yunnan and Sichuan (Szechwan) provinces of China, Assam of India, parts of Myanmar (Burma), Cambodia and Thailand (Siam). Botanical nomenclature of plants was initiated by the Swedish botanist Linnaeus, who first published the names of plants in Species Plantarum in 1753. He listed the tea plant as Thea sinensis, on page 515 of Volume I of Species
Plantarum, duplicated as Camellia sinensis on page 698 of Volume II of the same work.1 This had given rise to the debate on whether there are two species of tea, the large leaf variety originally found in Assam, India and the small leaf variety originally found in China.
Consequent to more detailed studies of the plant and the flower, botanists concluded that only one species existed, identified today as Camellia sinensis. The two main types are named as varieties, i.e. Camellia sinensis var. assamica
(Assam type) and Camellia sinensis var. sinensis (China type). A sub species of the tea plant known as the Cambod type, Camellia sinensis ssp. Lasiocalyx also exists. Genetic diversity studies carried out using modern molecular biology techniques have found that most tea plants in cultivation today are hybrids of these three.2
Discovery as a beverage and cultivation of tea started in China and derivatives of the Cantonese name ‘cha,’ or ‘tay’ in the Amoy dialect, are used all over the world to refer to the plant and the beverage.
Legendary Origin of the Tea Drinking Habit
The early history of tea is obscure and shrouded in mystery and legend. The story goes that the Chinese Emperor Shen Nung accidently discovered tea in 2737 B.C., whilst travelling through the countryside of his kingdom. Since the available water had been unfit for drinking, he had ordered his servants to boil the water and, whilst the open pot was on the fire, the wind had caused some leaves from a nearby tree to fall in to the pot. The Emperor, noticing the resulting aroma, had tasted the water and found it to be a very pleasant brew. Thus the consumption of tea as a beverage is said to have begun. It was not a surprising development as Emperor Shen Nung was a famous ‘herbalist,’ also known as the ‘Divine Healer,’ who often experimented with herbs and pronounced his opinion on them.
Emergence of Tea as a Medicinal Drink
It is evident from the early texts on Tea that in the beginning, tea had been considered a medicinal drink. Pen ts’ao, or Medical Book written in the Neo-Han dynasty, 25-221 A.D., the original authorship of which is ascribed to the Emperor Shen Nung, makes a reference to tea as “good for tumours or abscesses that come about the head, or for ailments of the bladder. It dissipates heat caused by the phlegms, or inflammation of the chest. It quenches thirst. It lessens the desire for sleep. It gladdens and cheers the heart.”
Another early reference to tea as a medicinal drink could be found in Shing lun by Hua T’o, a renowned physician and surgeon who died in 220 A.D. It says, “To drink K’u T’u (bitter tea) constantly makes one think better.”1 Reference to tea as K’u T’u had been made in several texts in this period, probably due to its preparation as a medicinal decoction from unprocessed green leaf.1
In the beginning, tea was exclusive to the Chinese royal circles and the royal tea gardens were protected to prevent tea from reaching the common man. Later, around the 6th century, tea reached common society and the Chinese generally began to regard tea not only as a medicinal drink but also as a beverage. According to the book Kuen Fang P’u, tea was first used as a beverage in the reign of Wen Ti of the Sui dynasty, 589-620 A.D. At that time it was considered as a good beverage but not esteemed. However,
its repute as a medicinal drink continued to be very high, as it was observed to be a remedy for “noxious gases of the body, and as a cure for lethargy”.1
Refinement of the Beverage
By the late 6th century, tea cultivation and tea drinking had spread widely in China and, during the Tang Dynasty (AD 618-907), a period of great prosperity in China, it had become the national drink. In 780 A.D., Lu Yu, a tea expert and noted author, published Ch’a ching or Tea Classic, which details the horticultural and other aspects of tea cultivation. It also gives the qualities and effects of the beverage. It quotes an emperor of the Han dynasty as, “The use of tea grows upon me surprisingly: I know not how it is, but my fancy is awakened and my spirits exhilarated as if with wine.”1 This indicates that improved manufacturing techniques had produced a better brew (probably black tea), as compared to the K’u T’u or bitter tea, previously prepared with unprocessed leaves. Lu Yu discusses the choice of the water to be used, and the degree to which it should be heated, indicating the developing refinements to the preparation of tea, as well as to the quality of the beverage.
Evolution and Spreading of Tea Drinking
The quality of the beverage would have attracted the attention of travellers to China and the awareness of tea and the tea drinking habit gradually filtered to other parts of the world, through travellers, traders and migrant workers
moving between neighbouring countries. Two Arabian travelers who visited China in 850 A.D., had spoken of tea as the common beverage in China, adding that the Chinese boil water and pour it over the tea leaf to prepare the beverage and that the Chinese believed that tea possessed medicinal properties.
Over time, initially in China, then in Japan, and thereafter spreading to other Asian countries, tea has evolved in to different forms and types, ranging from the sun-dried, steamed green, roasted green, non-fermented, semi-fermented, white tea and now, the most commonly consumed, black Tea.
From the very inception and up to the 19th century, tea drinking was a reverentially ceremonious custom, indulged in mainly by the royalty and nobility in the East and, even after its introduction to the West in the 17th century, a formal tradition observed only by the affluent, leisured classes of society. It did not reach the common citizenry, as a popular commodity till well into the 19th century.
Tea in Japan
Tea assumed a more important social cache’ in Japan than in China. Japanese Buddhist priests who pursued religious studies in China introduced tea to Japan, probably around 593 A.D., during the reign of Prince Shotoku. Later, priests brought tea seeds from China and introduced the cultivation of tea to Japan. It has been recorded that Buddhist monk Gyoki, 658-749 A.D., had built 49 temples and planted tea shrubs in the temple gardens.
The first book on tea in Japan, Kitcha Yojoki, The Book of Tea Sanitation, was written by the Buddhist priest Yeisai, chief of the Zen sect in 1191 A.D. He regarded tea as a sacred remedy and acclaimed tea as a “divine remedy and a supreme gift of heaven,” for preserving human life1.
Later the tea drinking habit became more widespread in the country. The invention of the green tea manufacturing process by San-no-jo in 1738 A.D. paved the way for tea drinking in all parts of the Japanese Empire.
Tea in Europe
The Portuguese were the first Europeans to arrive in the Orient by sea and establish trading connections, following Vasco da Gama’s discovery of the sea route to the east, via the Cape of Good Hope in 1497. Father Gasper da Cruze, a Catholic priest, returning to Portugal from China around 1560 recorded thus: “What so ever person or persons come to any man’s house of quality, hee hath a custom to offer him a kind of drink called ch’a, which is somewhat bitter, red and somewhat medicinall, which they are wont to make with certayne concoction of herbs.”
Later, Dutch and the English traders established trade with the East and introduced tea to other parts of Europe.
Early accounts by European authors suggest that tea was regarded as a medicinal drink by the Europeans also. Notable among them is an account given by the Dutch physician Dr. Nikolas Drix, 1593-1674 in Observationes medicae.
“Nothing is comparable to this plant. Those who use it are for that reason, alone, exempt from all maladies and reach an extreme old age. Not only does it procure great vigor for their bodies, but it preserves them from gravel and gallstones, headaches, colds, ophthalmia, catarrh, asthma, sluggishness of the stomach and intestinal troubles. It has the additional merit of preventing sleep and facilitating vigils, which makes it a great help to persons desiring to spend their nights writing or meditating.”1
Introduction of Tea to England
There is no record of the earliest importation of tea to England, probably taking place at the time of the introduction of tea to Holland, France and Germany. Shortly after 1644, English traders established themselves at the port of Amoy (Xiamen, in South East coast of China), which was their Chinese base for nearly a century. The Fukien dialect in the region refers to tea as “tay” and they spelled it as “t-e-a”. The English have, obviously, picked up the name for the beverage during this period.
Seventeenth century records show that the introduction of the beverage to England began in London coffee houses. The first public sale of tea was at the coffee house of Thomas Garway (or Garraway), in Exchange Alley, off Lombard Street, in 1657. As there was little general knowledge about tea at that time, Garway printed a broadside to inform the public about tea. In this famous pamphlet the virtues of tea are extolled as follows:
“It maketh the body active and lusty.
It helpeth the Headache, giddiness and heavyness thereof.
It removeth the obstructions of the Spleen. It is very good against the Stone and Gravel, cleaning the Kidneys and Uriters, being drank with Virgins Honey instead of Sugar.
It taketh away the difficulty of breathing, opening Obstructions.
It is good against Lipitude Distillations and cleareth the Sight.
It removeth Lassitude, and cleanseth and purifyeth adult Humors and hot Liver.
It is good against Crudities, strengthening the weakness of the Ventricle or Stomack, causing good Appetite and Digestion, and particularly for Men of a corpulent Body, and such as are great eaters of Flesh.
It vanquisheth heavy dreams, easeth the Brain, and strengtheneth the Memory.
It overcometh superfluous Sleep, and prevents Sleepiness in general, a draght of the Infusion being taken, so that without trouble whole nights may be spent in study without hurt to the Body, in that it moderately heateth and bindeth the mouth of the Stomack.
It prevents and cures agues, Surfets and Feavers, by infusing a fit quantity of the Leaf, thereby provoking a most gentle Vomit and breathing ofthe Pores, and hath been given with wonderful success.……” 1
This indicates that at the time of introduction of tea to England, its medicinal properties were already acclaimed.
Samuel Pepys 1633-1703, the Secretary to the Admiralty who kept a well-known diary, giving valuable details on daily life and customs of his time, makes a number of references to tea in the diary. The entry for Friday, 28 June 1667, includes “….. I went away and by coach hom, and there find my wife making of tea, a drink which Mr. Pelling the Potticary (Apothecary), tells her is good for her cold and defluxions…..”3 revealing that tea had been prescribed for some ailments.
Introduction of Tea to English Society
The Portuguese Princess Catherine of Braganza wedded Charles II in 1662. Apart from the cash dowry and the goods, sugar and spices she brought with her, she also carried a chest of tea, as Catherine was a tea addict. She was able to establish her favorite beverage, tea, as the fashionable drink in the court, influencing the replacement of ales, wines and spirits on special social occasions, with tea. Gradually, tea drinking became a habit of generations of British people. Even today it is a much treasured tradition. Britain, more than any other colonial power, played an important role in introducing tea to many other parts of the world.
Introduction of Tea to North America
Tea drinking was introduced to America, from Holland, in the middle of the seventeenth century Dutch New Amsterdam (at the southern tip of
the Manhattan Island), was the first American colony to drink the beverage. Later the English introduced the custom of tea drinking to New England. By 1763, when England had established a colonial administration in North America, it decided that the colony should be taxed to cover at least part of the cost for troops, deployed in its defence. However, the introduction of various forms of taxes strained the relationship between the colonists and the British Government and the Tax for Tea, through the Tea Act of 1773, was deeply resented by the American citizens. Ladies in many cities and villages pledged not to drink tea and even organised themselves into protest societies.
It has been recorded that in some parts of the country, it had been difficult to buy tea even for medicinal purposes without a permit from these societies, indicating that tea had been regarded as a medicinal drink in America too. One such permit issued in Wethersfield, Massachusetts reads:
To Mr. Leonard Chester SR:
Mrs. Baxter has applied to me for Liberty to buy a Quarter of a pound of Bohea (Black) Tea. I think by her Account of her age & bodily infirmities it will not be contrary to the Design of our Association to let her have it, & you have my full Consent thereto.
I am Yrs & c
ELISHA WILLIAMS
This movement against the British eventually led to the “Boston Tea Party,” where tea chests brought from England were destroyed by a group of colonists disguised as Indians, the episode eventually culminating in the American Revolution and the subsequent separation of the American colony from the British. The wharf where the tea was destroyed is now marked by a commemorative tablet reading:
HERE FORMELY STOOD
GRIFFIN’S
WHARF
At which lay on Dec. 16, 1773, three British ships with cargoes of tea. To defeat King George’s trivial but tyrannical tax of three pence a pound about ninety citizens of Boston partly disguised as Indians, boarded the ships, threw the cargoes, three hundred and fortytwo chests in all, into the sea, and made the world ring with the patriotic exploits of the
BOSTON TEA PARTY
Opening of Tea Plantations in Other Parts of the World
Java and Sumatra
After the tea trade was initiated by the Europeans, for many years it was believed that tea could be successfully grown and processed only in China and Japan. Later, the opening of new tea plantations by Europeans, in their Asian colonies, played an important role in the
development of the tea industry. Initially the Dutch opened plantations in Java and Sumatra.
In 1684, the German naturalist and Doctor of Medicine, Andreas Cleyer, brought tea seeds from Japan and planted them in his garden in Batavia (Jakarta) for ornamental purposes and therefore is credited as the first to grow tea in Java. Later, many private gardens in Batavia had established tea for ornamental purposes. Around 1830, seeds had been obtained from China and tea plantations had been gradually opened in Java and Sumatra.
India
Although the Dutch were the first to grow tea in Java and Sumatra, it was the English who gave impetus to tea cultivation, by launching very successful tea plantations in large areas of India and Ceylon. Concurrently, they established a lucrative trade in tea by promoting the consumption of tea throughout the world.
In 1823, Major Robert Bruce, whilst on a trade expedition to the province then known as Burmese Assam, found native tea trees growing in the hills. He arranged a supply of seeds and plants before his departure and these were planted in Gauhati and Sadiya in Assam. Later, many experiments had been carried out on commercial planting, using both China and Assam type plants. It was only in 1838 that shipments of black tea were made to the London auction. The plantations flourished and 788,842 acres were under tea by 1935.
Ceylon - Early History
Coffee was first introduced as a commercial crop in around 1830 and, till the emergence of the coffee blight – Haemilia Vastatrix – in 1868, enjoyed great success. In the interim, there had been several attempts by interested individuals, in experimental planting of tea in Nuwara Eliya and Pussellawa. However, none of these trials developed to a commercial level as the focus then was on coffee.
The first successful commercial trial of tea cultivation was by the Scotsman, James Taylor, who, in 1867, planted 20 acres of tea on Loolecondera Estate, Hewaheta, with an Assam type cultivar. This soon replaced coffee, then being rapidly ravaged by the coffee blight, and expanded quickly to other plantation areas of the country. By 1899, through the replanting of coffee areas and the opening of virgin land for planting, there were 400,000 acres under tea in Sri Lanka (Ceylon). The first export of 23 lbs in 1869 has now expanded to an annual average of 300 million kilograms of black tea.
Exclusivity of Ceylon Tea
In terms of grade variety, quality and spectrum of features of attractiveness, unarguably, Ceylon tea has no peer. Tea cultivation in Ceylon is divided in to 26 sub-districts and each region has its own special characteristics, in relation to elevation, climate, weather patterns, type and variety of cultivar, methods of cultivation, and variations/ refinements in manufacturing style. These factors invest Ceylon tea with that unique “Terroir,” as much as an equivalent diversity of conditions
provide the same degree of exclusivity to the best French wines.
Other tea-growing countries have introduced process developments and innovations to tea production, designed largely to meet mass marketing requirements, with the economies of scale as the primary objective, but that which has succeeded mainly in generating a boring homogeneity of product. The sameness of CTC tea is a typical example. However, the processing style in Ceylon remains largely traditional and still retains many of the original artisanal aspects of tea-making, designed to deliver to the consumer a tea with its innate goodness and authenticity intact, combined with a diverse product range, possible only within an orthodox style of manufacture.
In proportion to national output, the number of factories at over 400 in Ceylon is possibly the most numerous of any tea-growing country. The adherence to single origin sourcing amongst most local exporters, compelled largely by the current restrictions on the importation of tea, is another welcome point of departure from tea export processing industries in other countries. All these factors combine serendipitously to present a range of unique offerings to the customer, unmatched by any other producing country. Thus, the label attached to “Ceylon Tea” as the finest tea in the world, is justification of its merit.
Commenting on the ascent of the tea industry after the devastation of the coffee and its success, William H. Ukers in his monumental book on the tea industry, All About Tea (1935), has dedicated a
chapter to “Triumph of tea in Ceylon”1. Further, famous author Sir Arthur Conan Doyle, after his visit to Ceylon in 1921 had stated “… the tea fields of Ceylon are as true a monument to courage as is the lion at Waterloo”.3
Tea: Medicine or Beverage
The world view on tea has undergone several changes since its introduction to society. At the outset, in China and Japan, both from where the tea-drinking habit spread to other countries, it was, for many centuries, treasured for its medicinal properties. Later popularisation of the habit converted it to a common, but much appreciated beverage, with its health benefits taking second place. However, the rapidlydeveloping health consciousness within societies, in regard to food, drink and lifestyle, has refocused attention on the health benefits of tea, in this instance supported by the evidence of modern scientific research.
Resurgence of Medicinal Properties of Tea
With the advancement of medical sciences, life expectancy has gradually increased. This has resulted in the increase of the incidence of Non-Communicable Diseases, such as heart disease, stroke, cancer and diabetes. Gradually these diseases have become the major causes of death and disability in the elderly, affecting mostly people over 60 years of age. However, later, Non-Communicable Diseases have become more prevalent in younger generations as well, with large numbers above 40 years being affected in the new millennium.
Unhealthy lifestyles are the main cause of the increased incidence of these diseases. Unhealthy diet, sedentary lifestyle, tobacco and alcohol use and mental stress, have been identified as the major preventable causative factors. Among these, unhealthy diet is the major contributory factor for the causation of Non-Communicable Diseases.
The increasing incidence of such diseases has led to the scientific scrutiny of all dietary items, including beverages, to ascertain whether they are beneficial or harmful to human health. As tea is the most widely consumed beverage in the world, second only to water, from the 1980s onwards, reputed laboratories around the world have carried out wide-ranging research on the effects of tea consumption on human health.
To date such research has generated a vast array of information on the effects of tea consumption on human health. A search of the US National Library of Medicine database (PubMed) alone will generate the results of more than 40,000 related research studies. Thus, modern research has confirmed the age-old beliefs on health benefits of tea.
ɇ Botanical term for tea is Camellia sinensis.
ɇ Tea drinking and cultivation had originated in China around 6th century.
ɇ Tea was introduced to Europe in the 17th century.
ɇ At the beginning tea was considered a medicinal drink.
ɇ Tea plantations were established in other Asian countries, notably India and Ceylon (Sri Lanka) in the 19th century.
REFERENCES
ɇ By the 20th century tea had become the most consumed beverage, after water, in the world.
ɇ In the 1980s, modern scientific research had been initiated on medicinal properties of tea.
ɇ Today most consumers consider tea as a beverage which contributes to improve our health.
1. Ukers, William H., (1935), All about tea. The tea and coffee trade journal, New York.
2. Roy, S.C. and Chakraborty, B.N. (2009), Genetic diversity and relationship among tea (Camellia sinensis) cultivars as revealed by RAPD and ISSR based finger printing. Indian journal of Biotechnology, 8, 370-376.
3. Pepys, Samuel, Diary entry Friday 28 June 1667, available at www.pepysdiary.com, accessed on 5th September 2022
Types of Tea and Their Chemical Composition
Different types of tea are made from the tender shoots of the tea (Camellia sinensis) plant, the major types being black, green, oolong and white teas. The major water soluble components in the fresh, tender shoots, belong to the class of compounds called flavonoids. Both in green and white tea, the chemical composition is similar to that of fresh tender shoot, as only minor chemical changes take place during processing. Major chemical components present in fresh tender shoots, as well as in green tea and white tea, are flavanols (catechins) whilst in black tea most of the flavanols are converted to theaflavins and thearubigins. Theaflavin and thearubigin production take place during Oolong tea processing also, but to a lesser extent than in black tea.
The calorific value of tea is very low, as it contains very small amounts of carbohydrates, protein and fat, making it an ideal beverage for ‘calorie conscious’ individuals, whilst its very low sodium content makes it ideally suitable for those with a risk of high blood pressure. Sodium (a component in salt), contributes to increased blood pressure and thereby increases the risk of heart disease. Tea is a natural product as processing aids, preservatives and colouring agents are not used in the production process. All types of tea have similar health benefits, as they are made from the same raw material.
Raw materials used for the production of tea are the tender shoots of the tea (Camellia sinensis) plant. Generally, the unopened bud with the topmost two leaves, or ‘two leaves and a bud,' are plucked from the bush and transported for processing to the factory, which, in most instances, is situated within the plantation itself. The chemical composition of the shoot plucked for processing has the largest influence on the quality and taste of the final product.
TABLE 2.1 Chemical Composition of Tender Tea
Shoots 1, 2, 3
Water soluble Components Flavanols:
Partially Water Soluble Components
Water soluble compounds influence the taste and quality of tea, as these compounds, or their water soluble derivatives produced during processing, are eventually extracted into the brew and impart distinct characters.
Polyphenols
The terms polyphenols, tannins, flavonoids, flavanols and catechins are used to identify the major water soluble components of tea, giving rise to ambiguity. Often these terms are used in an interchanging manner. Further, terms such as EGCG, EGC, etc. are also used. The relationship between these terms is given in the chart below (Fig 2.1).
Figure 2.1 General structure of flavonoids with the numbering system
Polyphenols are a class of chemical compounds with particular structural features (with more than one phenolic unit) and occur naturally in all plants. Tannin is a word that has been used for certain types of polyphenols in the past due to their tanning (converting hide into leather) properties. However, tea polyphenols do not have tanning properties and, therefore, are no longer referred to as tannin. Flavonoids are a subclass of polyphenols with certain structural features (15-carbon skeleton, with two phenyl rings (A and B) and a heterocyclic ring (C). The carbon structure of the rings is often abbreviated as C6C3-C6. Polyphenols in tea belong to the sub-class flavonoids. Flavonoids have further subclasses and tea contains two of these, called flavanols and
flavonols. Flavanols (or flavan-3-ols) are the major components of tea with six compounds known as Epigallocatechin gallate (EGCG), Epigallocatechin (EGC), Epicatechin gallate (ECG), Epicatechin (EC), Gallocatechin (GC) and Catechin (C) (Table 2.1). All these six compounds are sometimes referred to as catechins. Tea also contains three flavonols called quercetin, myricetin and kaempferol.
The relative concentration of the flavanols, or their derivatives produced during processing, largely determine the quality of the final product. Interestingly, these compounds are also responsible for the most beneficial effects of tea.
Subclass 1
Subclass 2 Individual compounds
Polyphenols
Figure 2.2 Relationship between the terms used to describe polyphenolic tea components
Any plant will contain at least small amounts of polyphenols in all parts of the plant. Hence, any food product derived from a plant will contain at least trace amounts of polyphenols. A notable aspect in the chemical composition of all types of tea is the uniquely high polyphenol content, which could go up to 40% of the dry weight. Therefore, any type of tea would naturally contain very high amounts of polyphenols, compared to any other food item.
TABLE 2.2 Dietary sources of flavonoids4
Theobromine and Theophylline
The presence of the alkaloids, theobromine and Theophylline in tea has been established. Theobromine (which is also present in cocoa and chocolates) content is 0.1 to 0.4 while Theophylline is found in trace amounts. Theophylline relaxes the muscle around airways in the lung and makes breathing easier. Therefore, it is used as a drug in asthma and other lung diseases. Presence of trace amounts of theophylline could be the reason for relief in asthmatic patients after a cup of tea.
Theanine
- 36
- 33
Caffeine
Caffeine is an alkaloid present in tea. Contents could vary from 1.5 to 5% and the concentrations in green and black tea are similar1. Caffeine is the stimulant that gives the revitalizing effect to a cup of tea. It acts on the brain, increases alertness and also relieves fatigue (see chapter 13 for the effects of caffeine).
Theanine, an amino acid with a structure closely related to the protein forming amino acid glutamine, is unique to tea and not found in any other plant. It has a calming effect on the brain without sedation, unlike drugs used to induce calmness, which also produce sedative action, resulting in drowsiness. Therefore, if you work for long hours and feel tired, a break with a cup of tea would be ideal, as the unique combination of Caffeine and Theanine found only in tea, could restore you, relieve stress, and prepare you for extended hours of work. Recently, research has found that theanine contributes to reduced anxiety and stress and, also, could improve sleep quality (see chapter 13 for the effects of theanine).
Volatile Compounds
Although the concentrations are very low, volatile compounds contribute to both aroma and quality of tea. Under special climatic conditions found in certain tea-growing regions of the world, during certain months of the year, desirable volatile compound formation in tea could be enhanced.
Such teas are known as ‘seasonal teas’. Examples of much-sought-after seasonal teas in the world are, Darjeeling tea from India, and Uva, Dimbulla and Nuwara Eliya teas from Sri Lanka (see chapter 7 for details on seasonal teas).
Types of Tea Processed from the Tender Shoots of Camellia sinensis
Major types of tea produced in the world are black tea, green tea, oolong tea and white tea, the raw material for all being the tender shoots of the tea (Camellia sinensis) plant. The differences arise from variations in the processing. Black tea is the major type, accounting for approximately 78% of the global production. India, Sri Lanka and Kenya are the largest producers of black tea.
Green tea accounts for approximately 20% of the global production and China and Japan are the major producers. Oolong tea, produced only in Taiwan and in certain regions of China, accounts only for 2% of the world production. White tea is a highly-specialised product, generally produced using only the unopened bud. It is a delicate process and only small quantities are produced.
Herbal Infusions
Often, herbal infusions or “tisanes” made from other plants are also referred to as ‘tea,’ giving rise to ambiguity about such products. Generally, in such cases, a prefix is used to identify the plant used. e.g. chamomile tea. In certain parts of the world Rooibos tea, produced from the leaves of the Rooibos plant (Aspalathus linearis), is identified as ‘red tea’ or ‘red-bush tea’. However, the International Standards Organization (ISO)
STEPS IN THE PROCESSING OF BLACK AND GREEN TEA
Plucking
Tender Shoots
Withering (moisture reduced)
Steaming or pan firing (enzymes destroyed by heat)
Rolling (leaf macerated and broken)
Roll drying (leaf macerated, broken and dried)
‘Fermentation’
(enzymic conversion of catechins to theaflavins and thearubigins)
Drying
(enzymic conversion of catechins to theaflavins and thearubigins)
Black tea
(most of the catechins converted to theaflavins and thearubigins by enzymic reaction)
Green tea
(chemical composition similar to young shoots)
had recognised that tea is made only from the tea plant (Camellia sinensis). ISO has defined both black tea and green tea as products made “from the tender shoots of Camellia sinensis”.5, 6 When the word tea is used alone, it generally refers to the ‘true tea’ made from Camellia sinensis.
Beneficial Effects of Herbal Tea
Herbal teas are not produced from the tea plant (Camellia sinensis). Therefore, the effects of the consumption of herbal teas are quite different to that of tea. Generally a prefix (usually name of the plant) is used when referring to herbal teas (e.g. chamomile tea, peppermint tea, etc.)
Unlike with real tea, the effects of most herbal teas on human health have not been extensively studied. A large volume of research, especially human clinical trials on ‘real tea’, has enabled the proper scrutiny of the results through systematic reviews to arrive at correct and meaningful conclusions. However, when it comes to herbal teas, the health effects announced are sometimes based on very few studies or a single study. The majority of these studies are, generally, either in vitro studies (carried out in a test tube), or animal model studies, which cannot be extrapolated to predict what happens inside human body under similar circumstances. Only a very few human clinical trials have been conducted on the impact of consumption of herbal teas on human health, making it difficult to arrive at meaningful conclusions.
Although the consumption of certain herbal teas could impart beneficial effects, with currently available knowledge, it is very difficult to come to clear conclusions on the effect of regular
consumption of the majority of herbal teas on human health. Therefore, it is prudent to restrict consumption of herbal teas to occasional use.
On the other hand, any type of ‘real tea,’ made from the tender shoots of the tea plant (Camellia sinensis), could be considered the most suitable beverage for regular consumption, with proven health benefits for humans.
Information given in this article referring to ‘tea,’ apply only to ‘true tea,’ i.e. teas produced from Camellia sinensis. A description on some of the known facts about selected herbal teas are given in a separate section.
Black tea processing
After the fresh leaf is plucked, it is brought into the factory, which is generally situated in the tea plantation itself. Once inside the factory the leaf goes through five main stages in the process, called Withering, Rolling, Fermentation, Drying and Grading.
Withering
The objective of withering is to reduce the moisture content, preparing the leaf for the next stage in processing, which is rolling. If the fresh leaf is rolled, excessive leaf juice will be expelled,
removing some of the components required to make a good cup of tea. Although moisture reduction is the main aim of the withering process, certain chemical changes also occur in the leaf. When any part is removed from a plant, gradual dying of that part will start. In the tea leaf also, this will happen after plucking. In this process, the breakdown of large complex molecules, such as proteins and carbohydrates, to smaller units will take place. Some of these changes will enhance the quality of the end product, an example being the breakdown of protein to amino acids. These amino acids could further convert into desirable volatile compounds during the latter stages of processing, contributing to the aroma of tea.
The activity of certain enzymes in the leaf will also be increased during withering. Another important change is the gradual breakdown of cell membranes, making them more permeable and facilitating the mixing of components, which are spatially separated in the intact leaf, leading to reactions which are desirable for the quality of black tea. Moisture removal in black tea production is a slow process and requires between 6-18 hours, depending on ambient conditions and the standard and condition of leaf.
Withering troughs, in which air is passed through thick layers of leaf, are used for drying green leaf in the factory.
Rolling
The objective of rolling is to break the leaf into smaller parts and to macerate it, producing tea particles of desirable size and shape. The size and the shape of the particles will depend on the type of rollers used and the conditions used for rolling, which also determines the taste characteristics of the final product. Generally, several passes, often as much as four or five, are made through the rollers until all the leaves are reduced, by breaking, to the desirable size.
Orthodox, Rotorvane and Cut Tear and Curl (CTC) rollers are the main types of rollers used for tea processing. Orthodox rolling is a batch process, where leaves are fed into the roller and rolled for about twenty minutes before discharge. Rotorvane and CTC are continuous processes. Rolled leaves are referred to as ‘dhool,’ in the tea industry.
When orthodox rollers are used, as practiced in the low country regions of Sri Lanka, large wiry particles are obtained. In the up country region of Sri Lanka, after a single pass through an orthodox roller, rotorvanes are used for the subsequent passes, yielding much smaller broken particles. The CTC process, not common in Sri Lanka but widely used in India and Kenya, cuts the tea leaf into very small, even particles. It is a rigid process that does not permit variation and produces tea with uniform character, whilst the
orthodox process is very flexible and enables the production of a wide range of tea types, with both marked and subtle variations in appearance, character and liquoring properties, whilst retaining the inherent character of the tea.
As the leaf is broken up in the rolling process, the enzymes and their substrates, normally separate in the leaf, interact, resulting in certain enzymatic reactions which produce compounds that give black tea the typical taste and character. The most important change that is initiated with the assistance of the enzyme, Polyphenol Oxidase, is the conversion of Flavanols, or Catechins, the major components in the green leaf, to Theaflavins and Thearubigins. Theaflavins are golden yellow in colour and gives the brew a bright appearance, whilst contributing to astringency. Thearubigins are reddish brown and contribute to the colour of the brew, as well as the “mouth feel”.
When black tea particle size is small, extraction is faster when brewing a cup of tea. Therefore, most producers aiming for a uniform product for general consumers in tea bags will resort to the CTC process, which will give a coloury brew, very
quickly. Orthodox rollers and rotorvanes produce high quality, flavoury, teas with subtle differences, which would be more attractive to connoisseurs of tea.
Fermentation (Aeration, Oxidation)
In the fermentation stage, rolled leaf, or ‘Dhool’ are spread in layers 1 ½ to 2 inches thick on fermenting tables. Thin layers will ensure air (oxygen) supply to the particles which is required for the reactions and also prevent undesirable heat buildup. Dhool is retained on the fermenting tables, approximately for 2 to 3 hours, with the aim of allowing the enzymatic reactions to take place. Gradual change of colour from green to brown could be observed due to the breakdown of chlorophylls and, also, the formation of theaflavins
Orthodox roller
CTC roller
and later the thearubigins. Simultaneously, a change of aroma also takes place due to the formation of new volatile compounds.
In the CTC process, particle size is smaller, reaction rate faster and, consequently, difficult to control, resulting in the formation of higher amounts of thearubigins, giving greater colour to the brew. However, the reduction of Theaflavins will affect the brightness of the brew. Further, most of the desirable volatile compounds will be further converted to other compounds, resulting in a tea without an attractive aroma. Therefore, the CTC process will produce a uniform tea suitable for tea bags.
In the orthodox process, reactions take place at a slower rate and the character of the final product could be controlled by changing conditions, such as the pressure in the rollers, rolling time, fermentation time etc. This will allow an experienced ‘Tea Maker’ to produce a tea to suit the palate of a discerning consumer.
Historically, the term fermentation is used for a process where micro-organisms are involved in the production of alcohol from a substrate. The term had been introduced to tea processing, at a time when the process was not fully understood. However, micro-organisms are not involved in the process and alcohol is not produced. Only oxidation and other reactions take place with the aid of the enzymes found in the tea leaf itself. Therefore, now the trend is to identify the stage either as aeration or oxidation.
Drying
The objective of drying is to reduce the moisture content to about 3-4%, thus obtaining a stable end product. A hot stream of air is used for the final drying. When the particle size is small a Fluid Bed Dryer (FBD) could be used, where tea particles are fluidised by a stream of hot air. When the particle size is large, an Endless Chain Pressure (ECP) dryer is used, as it is difficult to fluidise the larger particles. A metallic chain conveys the tea particles through a stream of hot air in the ECP dryer.
Initially, when the temperature of the tea particles increases, the rate of enzymatic reactions will gradually increase. However, increase of temperature beyond a certain limit will destroy the enzymes and halt the enzymatic reactions giving a stable product. Most of the low-boiling volatiles and some of the high-boiling volatiles will also be lost during drying. The overall effect is a desirable one as most low-boiling volatiles are deleterious to the flavour of tea.
OrangePekoe(OP)
Broken OrangePekoe(BOP)
Grading
Dried tea is graded by being sequentially passed through a series of sieving machines. Sieves with the largest mesh size are placed on the top and the next size is placed under it. The sieves are mechanically vibrated and the tea is separated according to particle size. Main grades produced and the number of grades produced, could differ from factory to factory. However, generally, in a particular region most of the factories would make similar main grades.
A typical up country Sri Lankan factory would make four main grades: Orange Pekoe (OP), Broken Orange Pekoe (BOP), Broken Orange Pekoe Fannings (BOPF) and Dust. OP being the largest in size would come out from the top most sieve and Dust would be the smallest particles obtained from the bottom. In the low country Sri Lankan factories where only orthodox rollers are used, around sixteen to twenty grades are made.
Green Tea Processing
The main difference from black tea processing is subjecting the leaf to heat as the first step in the factory, in order to destroy the enzymes in the tea leaf. Subsequently, when the leaf is rolled enzymatic reactions will not take place. Therefore, unlike in black tea where new compounds are produced due to enzymatic reactions, in green tea the chemical composition of the final product is similar to that of fresh green leaf.
Mainly, two methods are used to subject the leaf to heat. Steam is used in Japan while in China, the leaf is subjected to heat in a pan (pan firing). If steam is used there could be a centrifugation step before the rolling to remove the moisture accumulated on the leaf. There is no fermentation stage in green tea processing, as there is no need to allow time for the enzymatic reactions. Generally, a sequence of rolling, partial drying followed by another rolling, and partial drying, is carried out until the moisture is reduced to the desired level.
Repeated rolling and drying gives the final product the much-valued shape. The shapes could range from needle-like thin strips, to small round hard pellets, resembling grains of gunpowder called ‘Gunpowder tea.’ Sometimes tea is ground to a powder. Some of the green teas are handmade to obtain specific shapes such as the ‘butterfly tea’.
Oolong Tea Processing
Oolong tea processing is similar to black tea processing, the main difference being a very short or absence of a fermentation stage. The aim is to initiate the enzymatic reactions but not to allow the reactions to complete. The result would be a product with taste and quality in between green tea and black tea, with a similar, in between chemical composition. If the fermentation period is very short the chemical composition and
taste would be close to that of green tea and if the fermentation period is longer the chemical composition and taste would be closer to that of black tea.
White Tea Processing
White tea is a special product which has been produced for a long time in small quantities, recent demand has resulted in an increased production. Traditionally, only the bud is used for production, with minimal processing and, in most cases, the bud is naturally dried in the shade. Sri Lankan ‘Silver tips’ is a type of white tea produced using this method, where buds of a special cultivar with purple leaves are used. Buds of this cultivar are larger and contain prominent leaf hairs, a desirable character in white tea. When well-made this cultivar produces tea of an attractive silver colour.
‘Golden tips’ made in Sri Lanka is also another sought after white tea, where the bud is hand
rolled lightly to stain the leaf surface and hairs, with the leaf juice. When done by an experienced tea maker, after drying, the bud and hairs will take an attractive golden hue.
Slightly different methods are used in other tea producing countries, where steaming the leaf, rolling and drying, using machinery, are also included in the processing. Sometimes, especially in China, the first leaf, together with the second leaf, are also used in the production of white tea.
The chemical composition of white tea is similar to that of green tea, as it is an unfermented tea. If only the buds are used for the production, the total polyphenol content could be relatively higher than in other types of tea, as the bud contains higher amounts than the first leaf or the second leaf.
Chemical Composition of Black and Green Tea Brew
TABLE 2.3 Chemical composition of a typical tea brew2
are classified as flavonoids and these two components have beneficial properties similar to catechins. All the other components have similar concentrations in both black and green tea brews.
All types of tea provide similar health benefits. Therefore, choice of tea could be made purely on taste preferences.
Nutrients in Tea
Major Nutrients and Calorific Value of Tea
Major nutrients in food are carbohydrates, proteins and lipids (fat). These are mainly used by our body to obtain energy and also as structural components. Tea contains very low amounts of these major nutrients (Carbohydrates 4%, lipids 3% and proteins 6% - Table 2.3). Approximately 2-3 grams of tea are used to brew a cup of tea. Therefore, the amount of carbohydrates in a cup of tea (without milk and sugar), would be 80-120 mg. This could be termed as a trace amount if we compare it with other food.
During black tea processing, most of the flavanols in the fresh green leaf are converted to theaflavins and thearubigins, whilst relatively small amounts of flavanols remain without change. This is reflected in the tea brew. In the green tea brew, the major constituent are flavanols. Theaflavins and thearubigins are not found in green tea. This is the major difference that could be observed between black and green tea brews. Theaflavins and thearubigins
A very thin slice of bread would approximately contain 15 g (15,000 mg) of carbohydrates. Similarly lipid (fat) content and protein content is also very low in a cup of tea. Thus, it is very clear that tea does not contribute a significant amount of major nutrients. Calorific value of a cup of tea would be almost zero. To those trying to minimise daily calorie intake, a cup of tea between main meals, instead of a snack, would be a great boon.
Vitamins in Tea
Although fresh tea leaf contains vitamin C and E, the major proportion of these are lost during processing and the brewing of tea. However, certain components in the vitamin B group could come into the brew. Only thiamin and folate make a significant contribution to the daily intake.
TABLE 2.4 Contribution of vitamins from tea to the daily intake7
TABLE 2.5 Contribution of minerals from tea to the daily intake8
Minerals in tea
Some of the minerals in tea are not extracted into the brew, whilst some of the minerals extracted into the brew are poorly absorbed by the gastrointestinal tract into the body. Therefore, what is important is to look at the minerals which make a significant contribution to the daily intake (Table 2.5).
Tea is a rich source of manganese and one litre of tea (approximately 6 cups), would provide about 45% of the daily requirement. However, manganese deficiency is very rare in humans and the required amounts could be obtained even without drinking tea. Further, manganese toxicity due to excessive intake is not observed even in populations of heavy tea drinkers.
It is interesting to note that contribution to the aluminum intake is only 2.8%, proving that tea does not contribute significantly to the daily aluminum intake, though the relatively high concentration of aluminum in the mature tea leaf had led to the erroneous conclusion in the past that tea drinking could lead to aluminum toxicity. However, only the tender leaf, where the aluminum concentration is several fold less than in the mature leaf, is used for processing.
Tea contains very small amounts of sodium and, therefore, it makes only an insignificant contribution towards daily intake. Excessive
intake of salt, which is sodium chloride, could increase the risk of high blood pressure, which, in turn, increases the risk of heart disease. According to the World Health Organization (WHO) guidelines, daily sodium consumption should be less than 2 g (5 g of salt)9, though the majority of the world population exceeds these limits. According to the US – FDA, the average intake in US is 3.4 g, whilst it is 8-12 g in the European Union, according to the European Commission10, 11. Due to the adverse effects of high salt intakes on humans, many countries have started salt reduction programmes. Choosing tea as a beverage for regular consumption would help in reducing salt consumption, as any other beverage would have higher amounts of sodium than in tea.
Natural Product
In the production of all types of ‘true tea’ only the tender shoots of the tea plant are used. Chemicals are not used as processing agents during the processing of tea. Neither preservatives nor colouring agents are added to the final product. Therefore, tea could be termed a natural product.
ɇ Different types of tea – black, green, oolong and white tea – are made from the tender shoots of the tea plant (Camellia sinensis)
ɇ The major component in tea shoots are flavanols (also called as catechins), which belong to the class of chemical compounds called flavonoids.
ɇ In green tea, flavanols remain unchanged while during black tea production, most of the flavanols in the fresh leaf are converted to theaflavins and thearubigins, which give the characteristic colour and taste to the black tea brew.
ɇ Flavanols, theaflavins and thearubigins have similar beneficial properties. Therefore, all types of tea have similar health benefits.
ɇ Calorific value of tea is almost zero, which makes it an ideal beverage for calorie conscious individuals.
ɇ Tea contains very low sodium (salt is sodium chloride) levels, making it a suitable beverage for protection against developing high blood pressure and, thereby, reducing the risk of heart disease.
ɇ Tea is a natural beverage, as processing aids, preservatives or colouring agents are not used in its production.
REFERENCES
1. Engelhardt U.H., 2010, Chemistry of tea, In: Comprehensive natural products II, pp 999-1032
2. Harbowy M.E, Balentine D.A., Davies A.P. and Cai Y., 1997, Tea Chemistry, Critical Reviews in Plant Sciences, 16:5, 415-480
3. Balentine D.A., Wiseman S.A. and Bouwens L.C.M., 1997, The chemistry of tea flavonoids, Critical Reviews in Food Science and Nutrition, 37:8, 693-704.
4. Balentine, D.A., 2001, The role of tea flavonoids in cardiovascular health. Proceedings of International Conference on O-Cha (Tea) Culture and Science, Session III, Shizuoka, Japan, pp 84-89.
5. ISO 3720:2011 Black tea: Definition and basic requirements, International Standards Organization.
6. ISO 11287:2011 Green tea: Definition and basic requirements, International Standards Organization.
7. Stagg G.V. and Millin D.J., 1975, The nutritional and therapeutic value of tea, Journal of the Science of Food and Agriculture, 26, 1439–1459
8. Powell J.J., Burden T.J. and Thompson R.P.H., 1998, In vitro mineral availability from digested tea. Analyst, 123, 1721-1724
9. World Health Organization (WHO), Salt reduction, Fact sheet – Available at www.who.int/news-room/fact-sheets/detail/salt-reduction Accessed on 5th September 2022
10. US FDA Sodium reduction – Available at www.fda.gov/food/food-additives-petitions/sodium-reduction#:~:text=The%20Dietary%20 Guidelines%20for%20Americans%2C%202020%2D2025%20recommends%20limiting%20sodium,those%2013%20years%20and%20younger. Accessed on 5th September 2022
11. Survey on the member states implementation of the EU salt reduction framework – Available at data.europa.eu/doi/10.2772/50212
“I
know very well that I am in a minority here. But still, how can you call yourself a true tea-lover if you destroy the flavour of your tea by putting sugar in it? It would be equally reasonable to put pepper or salt. Tea is meant to be bitter, just as beer is meant to be bitter. If you sweeten it, you are no longer tasting the tea, you are merely tasting the sugar; you could make a very similar drink by dissolving sugar in plain hot water.”
George Orwell, “A Nice Cup of Tea,” Evening Standard, 12 January 1946
A Healthy Diet for a Healthy Life
Unhealthy lifestyles have resulted in the increased incidence of Non-Communicable Diseases (NCDs) globally, whilst increased life expectancy has aggravated the burden of NCDs. Unhealthy diet, sedentary lifestyle, tobacco and alcohol use and mental stress, are some of the major preventable aspects amongst the factors that affect human health. Of these, unhealthy diet is the major contributory factor for Non-Communicable Diseases. Thus, a diversified, balanced and healthy diet, throughout the lifespan is essential for good health. Excessive calorie and salt (sodium) intakes are the two major and common issues associated with an unhealthy diet. The former leads to obesity and NonCommunicable Diseases whilst the latter leads to high blood pressure.
Often, individuals do not pay attention to the importance of beverages when evaluating their diet, though beverages account for 20% of the total calorie intake. Therefore, the choice of beverages merits as much attention as solids in one’s selection of food for regular consumption. As a beverage closest to water, whilst containing very minimal amounts of salt and almost zero calories, tea presents itself as the most natural and most logical alternative for regular consumption. Research has also revealed that flavonoids in tea could reduce the risk of NCDs.
Life Expectancy
Average global life expectancy at birth was 73.4 years in 2019, whilst in 1960 the same rating had been 52.5 years. Initially increasing only gradually, life expectancy has increased by more than 6 years between 2000 and 2019 – from 66.8 years in 2000 to 73.4 years in 2019, while healthy life expectancy has also increased from 58.3 in 2000 to 63.7 in 2019. However, the increase in healthy life expectancy (5.4 years) has not kept pace with the increase in life expectancy (6.6 years). The increase in life expectancy is primarily due to the availability of improved medical care, resulting in the containment or eradication of most infectious diseases, which were the major causes of mortality in the past.1 For example, out of 15 million small-pox patients in 1967, 2 million died. However, by 1979 the disease was considered eradicated, worldwide, by successful vaccination programmes. Similarly, effective medications have been discovered for other diseases such as malaria, which, in the past, were deadly afflictions.
Burden of Disease in the Elderly
A major negative aspect of increased life expectancy is the corresponding increase in NCDs, particularly heart disease, stroke, diabetes, high blood pressure and cancer. According to the World Health Organization (WHO), leading causes of death at present are, heart disease with 8.9 million, Stroke at 6.7 million, diabetes at 1.5 million and lung cancer at 1.2 million. Thus, whilst life-expectancy has increased, the quality of life of the elderly has declined due to NCDs.
According to the WHO, whilst the global average life expectancy in 2019 was 73.4 years, the healthy life expectancy is only 63.7 years, indicating that most of the elderly global population would be burdened with diseases in the latter part of life, leading to an increase in health-related expenditure.1 The annual average healthcare expenditure in the over 65 group in the US was USD 11,089, whilst in the working age group (19-65 years), it was USD 3352.2 Where health care is provided by the State, cost of care of the elderly has become a large proportion of national expenditure, whilst in other countries it has become the burden of the individuals themselves, as well as that of the families and support groups.
Lifestyle and Non-Communicable Diseases
Whilst advancing age results in a natural increase in the risk of most NCDs, apart from increased lifespan, lifestyle is also a major influential factor. This applies to the young as well, observed as a recent emerging trend. According to the WHO, healthy life expectancy could improve by 5-10 years, merely with the adoption of a preventive or healthy life-style.
Factors that Affect Health
Genetics, or inherited character, is outside individual control and a family history for cardiovascular disease or stroke, for instance, increases an individual’s risk for such diseases. Ethnicity is yet another contributory factor, with African-Americans, for example, demonstrating a higher level of risk for certain NCDs than whites living in the US. However, apart from ageing
and inheritance, preventable factors, such as sedentary lifestyle, tobacco and alcohol use and mental stress, are hugely influential on individual health.3
Sedentary Lifestyle
Humans are spending increasing amounts of time in activities requiring minimum physical activity. Most innovations are designed to minimise human movement and muscular activity at home, work place, schools and public spaces, resulting in a sedentary life for the majority. From an evolutionary perspective humans have the capacity to be mobile throughout the day. The shift from a physically demanding life to a sedentary life is sudden, as it has occurred during a tiny fraction of human existence. Further, during the past twenty years, ‘screen time’, such as using computers and smart phones, watching television, playing video games, surfing the web, all sedentary activities, has increased dramatically.
Scientific research on the impact of decreased physical activity and the correlation on physical work, energy expenditure and health indicate that a sedentary lifestyle could lead to heart disease, diabetes, obesity and some types of cancer. Therefore, current public health recommendation is to engage in at least 20 minutes of moderate to vigorous activity per day (150 minutes per week).4
Tobacco and Alcohol use
Scientific research has provided clear evidence on the increased and dose dependent (higher the dose higher the risk) relationship, between tobacco use and cancer in the oral cavity throat
and lungs. In addition, it has a similar relationship with heart disease too. Therefore the current public health recommendation is to completely avoid tobacco.
In 2012, 3.3 million deaths (5.9% of global deaths) were due to alcohol consumption, which has a complex relationship with health. Research has clearly shown that heavy drinking could lead to many disease conditions, while moderate drinking may have beneficial effects on heart disease.5 Moderate alcohol consumption is defined as up to 1 drink per day for women and up to 2 drinks per day for men. One drink is defined as a drink that contains approximately 14 grams of pure alcohol, which is found in:
ɇ 12 ounces (~350 ml) of regular beer, which is usually about 5% alcohol
ɇ 5 ounces (~150 ml) of wine, which is typically about 12% alcohol
ɇ 1.5 ounces (~50 ml) of distilled spirits, which is about 40% alcohol 6
However, the issue is that moderate consumption carries the potential for abuse in the long-term.
Mental Stress
All animals, including humans, have a stress response, essential in certain situations such as confrontation with danger, when the hormones released in response prepares the animal either to face danger or flee from it. Pulse rate increases, breathing becomes faster, muscles tense and the brain uses more oxygen, gearing the animal for survival.
In the short term stress is useful and does not affect health. However, with chronic or prolonged stress, the same chemicals and hormones carry the potential for conditions such as mental disorder and depression, paving the way for NCDs such as impaired immunity, increased risk of heart disease, high blood pressure and diabetes.
Common factors which cause prolonged stress are:
ɇ Routine stress related to the pressures of work, family, and other daily responsibilities.
ɇ Stress brought about by a sudden negative change, such as losing a job, divorce, or illness.
ɇ Traumatic stress, experienced in an event like a major accident, war, assault, or a natural disaster, where one may be seriously hurt or be in danger of being killed.
Seeking guidance from qualified healthcare personnel is important, to cope with prolonged stress.
7
Diet
According to the WHO, diet plays the most crucial role in the development of NCDs, with unhealthy diet being a leading global factor affecting general health. Adopting healthy dietary habits early, and adhering to such throughout, could protect against NCDs such as heart disease, cancer, stroke and diabetes. Breast feeding, too, fosters healthy growth and improves cognitive development and, in the long-term, contributes to minimising the risk of obesity and the consequent development of NCDs.
Rapid urbanisation, changing lifestyles and increased production of processed food have changed dietary patterns globally, with a large proportion of the global population consuming more food than necessary, leading to obesity and the development of NCDs. People generally are consuming food high in energy, fat, free sugars and salt/sodium, at the expense of healthy food such as fruit, vegetables and whole grains, which are high in dietary fibre.
The nature and composition of a balanced, diversified diet will vary depending on individual needs (age, lifestyle, degree of physical activity) and the individual’s cultural context. However, irrespective of all circumstances, the basic principles of what constitutes a healthy diet will not vary.
According to the WHO guideline a healthy diet for adults should contain:
ɇ Fruits, vegetables, legumes (e.g. lentils, beans), nuts and whole grains (e.g. unprocessed maize, millet, oats, wheat, brown rice).
ɇ At least 400 g (5 portions) of fruits and vegetables a day. (Potatoes, sweet potatoes, cassava and other starchy roots are not classified as fruits or vegetables.)
ɇ Less than 10% of total energy intake from free sugars, which is equivalent to 50 g (or around 12 level teaspoons) for a person consuming approximately 2,000 calories per day, but ideally less than 5% of total energy intake for additional health benefits. Most free sugars are added to food or drinks by the manufacturer, cook or consumer, and can also be found in sugars
naturally present in honey, syrups, fruit juices and fruit juice concentrates.
ɇ Less than 30% of total energy intake from fats. Unsaturated fats (e.g. found in fish, avocado, nuts, sunflower, canola and olive oils), are preferable to saturated fats (e.g. found in fatty meat, butter, palm and coconut oil, cream, cheese, ghee and lard). Industrial trans fats (found in processed food, fast food, snack food, fried food, frozen pizza, pies, cookies, margarines and spreads), are not part of a healthy diet.
ɇ Less than 5 g of salt (equivalent to approximately 1 teaspoon) per day and use iodised salt.3
Beverages
Beverages are often not considered when individuals think about overall food intake, though regularly consumed beverages have a great influence on our health. Additional calorie intake is one of the main issues related to inappropriate beverage choices. According to 2020-2025 Dietary Guidelines for Americans, beverages account for 20% of total calorie intake.6
Therefore, careful attention should be paid to the calorie intake from beverages. Beverages selected for regular consumption should be very close to water in calorie and salt content, whilst hydrating the body. Water has neither calories nor salt and hydrates the body.
Tea
Tea (without milk or sugar) fits this description, as it contains almost zero calories and very low amounts of sodium (see chapter 2 for chemical composition of tea). Further, scientific research has revealed that tea contains high amounts of flavonoids, which could reduce the risk of NonCommunicable Diseases. Therefore, tea is an ideal beverage for regular consumption.
ɇ Unhealthy diet is a major contributory factor for the risk of Non-Communicable Diseases.
ɇ A diversified, balanced, healthy diet throughout the lifespan is essential for good health.
ɇ Although beverages contribute significantly to the calorie and salt intake, adequate attention is not paid to regularly consumed beverages when healthy diets are planned.
ɇ Tea, having almost zero calories and very low salt content and high flavonoid content, would be an ideal choice as a beverage for regular consumption that could also reduce the risk of Non-Communicable Diseases.
REFERENCES
“Each cup of tea represents an imaginary voyage.”
Catherine Douzel
1. Global health observatory data, World Health Organization. Available at www.who.int/gho/mortality_burden_disease/life_tables/en/ Accessed on 16th August 2022
2. The high concentration of US healthcare expenditure, Research in Action, Issue 19, Agency for healthcare research and quality, US Department of health and human services. Available at archive.ahrq.gov/research/findings/factsheets/costs/expriach/ Accessed on 16th August 2022
3. Healthy diet, Fact Sheet No. 394, World Health Organization. Available at www.who.int/mediacentre/factsheets/fs394/en/ Accessed on 16th August 2022
4. Sedentary behaviour: Emerging evidence for a new health risk. Mayo clinic proceedings, 2010 Dec., 85(12), 1138-1141
5. Alcohol: facts and statistics, U.S. National Institute of alcohol abuse and alcoholism, Available at www.niaaa.nih.gov/alcohol-health/ overview-alcohol-consumption/moderate-binge-drinking Accessed on 16th August 2022
6. 2020–2025 Dietary Guidelines for Americans. 9th Edition. December 2020, U.S. Department of Health and Human Services and U.S. Department of Agriculture. Available at www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_ Americans_2020-2025.pdf Accessed on 16th August 2022
7. Fact Sheet on Stress, U.S. National Institute of Mental Health. Available at www.nimh.nih.gov/health/publications/stress/index.shtml Accessed on 16th August 2022
Antioxidants in Tea
Reactive oxygen species (ROS) and free radicals (FR) are highly reactive molecules that have the potential to damage other molecules in the human body. These could be naturally generated in the body and could also enter the body through inhalation of polluted air, smoking and contaminated food. The presence of excessive amounts of ROS and FR is called ‘oxidative stress’.
Prolonged oxidative stress has been found to be one of the key factors in the development of Non-Communicable Diseases (NCDs), such as heart disease, stroke, cancer, diabetes and neuro-degenerative diseases. The human body has protective mechanisms against oxidative stress, through antioxidant enzymes and antioxidant molecules. In addition, antioxidant molecules derived from the diet also play an important role in the protective mechanism against oxidative stress. Antioxidants in the diet include vitamin C, vitamin E, carotenoids and plant flavonoids.
Tea has been identified as a plant with uniquely high flavonoid content. Therefore, all types of tea have high antioxidant capacity compared to other food. Antioxidant activity of tea flavonoids has been demonstrated in both in vitro and in vivo experiments. Tea flavonoids have the ability to neutralise or scavenge the FR and ROS in the human body. Research has indicated that tea flavonoids are capable of exerting antioxidant activity through other mechanisms, in addition to scavenging of FR and ROS. Therefore, regular tea consumption would have beneficial effects through the antioxidant activity of flavonoids.
Antioxidants
In recent times, antioxidants have become a ‘buzzword’ in relation to food. People have become interested in antioxidants in food, as antioxidants have the ability to effectively limit the damage caused to our bodies by certain molecules, which are either produced internally, or enter from outside. These harmful molecules are referred to as free radicals (FR) and reactive oxygen species (ROS).
Free Radicals and Reactive Oxygen
Species
Most molecules in our body are fairly stable and unreactive. They undergo reactions only when they enter natural metabolic processes, essential for normal functioning, that take place in our body.
In contrast, free radicals are highly unstable molecules. In order to stabilise, they react with any other molecule in the vicinity. This process, whilst stabilizing the free radical, damages the molecule that it reacts with, often making it a free radical. The newly-generated free radical would react with another molecule to stabilise itself, thereby initiating a chain reaction. Thus the presence of free radicals in our body could initiate a chain of reactions that would damage other important molecules in human body and, unchecked, has the potential to disturb its normal functioning. Further, damage to certain types of molecules could play an important role in the development of NCDs, such as heart disease, stroke and cancer.
Reactive oxygen species (ROS) are highly unstable reactive molecules that contain oxygen, which are present in the body. Over-production and accumulation of ROS could also initiate chain reactions that could potentially lead to NCDs. Presence of excessive quantities of FR and ROS will subject the body to ‘oxidative stress’.
The accumulation of FR and ROS in the human body could take place either through production in the body itself or through exposure to FR and ROS from outside.
Production of FR and ROS could take place in the normal metabolic processes that take place in our body. For example, energy required for the functioning of the body is obtained by utilisation of energy stored in carbohydrates, fat or proteins, a process called ‘cellular respiration’. In cellular respiration, oxygen reacts with glucose (or other stored energy producing molecules), producing water, carbon dioxide and energy. This is similar to burning fuel to obtain energy. When firewood or petroleum products are burned energy in the form of heat is produced. However, production of toxic compounds, which are in the smoke, cannot be avoided in the process.
Energy production in the body is also a process of burning fuel, which are carbohydrates, fat or protein that come from our diet. Production of toxic molecules such as FR and ROS cannot be avoided in cellular respiration either. However, the process inside the body is much more controlled and the amounts of toxic material produced is far less than in burning of firewood or petroleum products. In addition to cellular respiration, many
other biochemical processes take place inside the body, which could also produce FR and ROS.
FR and ROS, and other toxic material, could enter the human body from outside, through the inhalation of polluted air or in the food consumed. Another common method of exposure to FR, ROS and other toxic compounds is smoking. Smokers voluntarily expose themselves to the toxic material in tobacco smoke. Diet could also contain toxic molecules due to contamination and adulteration. Common contaminants are pesticide residues in agricultural products and aflatoxins due to fungal contamination, though all contaminants are not either FR or ROS.
The human body always tries to excrete toxic molecules as quickly as possible through urine, by converting the toxins to water soluble compounds. Sometimes FR and ROS could be produced in the detoxification process also. Exposure to ionising radiation such as ultra violet (UV) light could also produce FR and ROS in the body, which often leads to skin cancer. Further, heavy metals could also facilitate the generation of FR and ROS in the body.
Free Radicals and Reactive Oxygen Species in the Development of Non-Communicable Diseases
Oxidative stress has been implicated in the development of many NCDs. For example, reaction of FR and ROS with DNA (deoxyribonucleic acid), the genetic material in our body which carries the genetic instructions used in the growth, development, functioning and reproduction, have
the potential to disrupt some of these processes. More importantly, DNA damage could lead to carcinogenesis.1
Through similar mechanisms, prolonged oxidative stress could potentially lead to the development of other NCDs, such as heart disease, stroke, neurodegenerative diseases and diabetes.2, 3, 4
Antioxidants and Antioxidant
Mechanisms on FR and ROS
FR and ROS in the body should be neutralised to avoid prolonged oxidative stress, which could predispose the individual to NCDs. Antioxidants are capable of neutralising (or scavenging) FR and ROS.
The human body has natural antioxidant defence systems, which harness enzymes and other molecules with the capability of neutralising the FR and ROS. Super Oxide Dismutase (SOD), Catalase (CAT), Glutathione Peroxidase (GTPx), Glutathione Transferase (GTS) are the important antioxidant enzymes in the human body, with the Glutathione system being one of the most important.5
In addition to the above, certain molecules, such as Vitamin C (Ascorbic Acid) and Vitamin E (α-Tocopherol), play an important role in the anti-oxidant defence mechanism. Carotenoids and plant flavonoids are also such important antioxidant molecules.
Plant Flavonoids
Plants produce flavonoids for various reasons and play an important role in the interaction of plants with other organisms in the environment. They display anti-feeding activity against insect pests, and anti-fungal activity towards pathogenic fungi. Therefore, plant flavonoids are important in the plant defence systems. Thus all plants contain varying amounts of flavonoids, distributed in all parts of the plant.6 As such, food derived from plant sources would contain varying amounts of flavonoids.
Flavonoids in Tea
Fresh tender shoots of tea, which are used for processing into different types of tea such as black tea, green tea and oolong tea, contain significantly high amounts of flavonoids compared to other plants. Therefore, a serving of any type of tea would provide significantly higher amounts of flavonoids than a serving of other flavonoid containing food.
Fresh tea shoots contain flavanols as the major water soluble component (18-32%) and flavonols (3-4%). During black tea processing most of the flavanols are converted to other types of flavonoids (theaflavin and thearubigins), while in green tea processing they remain unchanged. Flavonols remain unchanged during processing in both types of tea. (See chapter 2 for details on flavonoids in tea)
Due to the high content of flavonoids in tea, antioxidant activity of all types of tea would be significantly higher than any other food. Dietary surveys on the total flavonoid intakes have shown
that tea is the major source of flavonoids, even in countries which are not considered as major tea consuming countries, emphasising the high flavonoid content in tea. Zutphen elderly study in the Netherlands and the dietary survey on flavonoid intake of US adults are two such studies 7, 8
Comparison of Antioxidant Capacity of Tea and Common Vegetables
FIGURE 4.1 Total antioxidant capacity of tea and common vegetables9
Green tea
Black tea
Garlic
Kale
Spinach
Brussels sprouts
Alfalfa sprouts
Broccoli flowers
Beets
Red bell pepper
Onion
Corn
Egg-plant
Cauliflower
Potato
Sweet potato
Cabbage
Leaf lettuce
String bean
Carrot
Yellow squash
Iceberg lettuce
Celery
Cucumber
ORAC as micromol of Trolox equivalent/g of dry matter
Health and Antioxidant Activity of Tea
The majority of the health benefits of tea are due to the antioxidant activity of flavonoids in tea. Therefore, early research on health benefits of tea consumption mainly focused on establishing the antioxidant activity of tea flavonoids. Antioxidant activity of tea flavonoids and tea brew had been demonstrated, both in vitro (outside living organisms) and in vivo (inside living organisms) in these early experiments. Later these studies have been extended to find the mechanisms through which antioxidant flavonoids in tea could reduce the risk of NCDs.
Strong antioxidant activity of tea extracts, and individual flavonoids in tea, has been well established, in vitro, using Trolox Equivalent Antioxidant Capacity (TEAC), Oxygen Radical Absorbance Capacity (ORAC) and many other assay methods.10, 11 The next question that arises is whether these tea flavonoids are absorbed from the digestive tract and whether they could act as antioxidants in vivo too. Bio-availability (whether a compound is absorbed from the digestive tract and reaches the blood stream to make it available) of plant flavonoids and especially tea flavonoids, has been established in many studies.12
It has been found, that micro-flora living in the digestive tract of humans aid the absorption of flavonoids by converting them into easilyabsorbable forms.13 In vivo antioxidant activity also has been well established, using both animal model and human studies.14, 15 Comparison of in vivo antioxidant potential of catechins (in green tea) and theaflavins (in black tea) revealed that
they are equally effective antioxidants.16 In vivo antioxidant activity of thearubigin fraction of black tea also has been established.17
Often, milk is added to tea by many consumers in different parts of the world. Milk proteins and tea flavonoids are known to interact with each other. Therefore, there was a doubt whether addition of milk would reduce the antioxidant activity of tea. It has been found that addition of milk does not alter the antioxidant activity and tea, with or without milk, increases the antioxidant activity of humans by similar amounts.18
Research has shown that in addition to scavenging FR and ROS, tea may exert antioxidant activity through other mechanisms too. Tea flavonoids, after entering the human body, have the ability to enhance the activity of antioxidant enzymes such as superoxide dismutase (SOD), and the enzymes in the glutathione system, improving the natural antioxidant defences of the body19.
There are certain other enzymes in the human body, called pro-oxidant enzymes, such as Nitric oxide synthase, lipoxygenase and cyclooxygenase, whose activity could result in the generation of oxidant molecules. Tea flavonoids have the ability to inhibit such enzymes20. Further, excessive amounts of free metal ions in blood and other body fluids, would facilitate the activity of oxidant (FR and ROS) molecules in the body. Tea flavonoids could bind with free metal ions in blood and body fluids and, thus, contribute to the antioxidant activity in vivo21.
Certain molecules in the human body act as messengers and play an important role in the biological processes that take place inside. Some of those messengers could promote pro-oxidant activity. Studies have found that tea flavonoids could inhibit some pro-oxidant messengers. Inhibition of nuclear factor κB (NF κB) is one such example22.
ɇ Reactive oxygen species (ROS) and free radicals (FR) are highly reactive molecules, that could damage other molecules in the human body, potentially leading to NonCommunicable Diseases such as heart disease, stroke, cancer, diabetes and neurodegenerative diseases.
ɇ Presence of excessive amounts of ROS and FR is known as ‘oxidative stress’.
ɇ Antioxidants derived from diet play an important role in reducing oxidative stress.
ɇ Tea contain very high amounts of antioxidant flavonoids that could contribute to reduce oxidative stress.
ɇ Regular tea consumption could have beneficial effects on human health through its antioxidant flavonoids.
REFERENCES
1. Cheng Guo, Xiaofen Li, Rong Wang, Jiekai Yu, Minfeng Ye, Lingna Mao, Suzhan Zhang, and Shu Zheng, 2016, Association between Oxidative DNA Damage and Risk of Colorectal Cancer: Sensitive Determination of Urinary 8-Hydroxy-2′-deoxyguanosine by UPLC-MS/ MS Analysis., Science Reports, 6, 32581.
2. Nageswara R. Madamanchi, Aleksandr Vendrov, Marschall S. Runge, 2005, Oxidative Stress and Vascular Disease, Arteriosclerosis, Thrombosis and Vascular Biology, 25, 29-38
3. Raynoo Thanan, Shinji Oikawa, Yusuke Hiraku, Shiho Ohnishi, Ning Ma, Somchai Pinlaor, Puangrat Yongvanit, Shosuke Kawanishi and Mariko Murata, 2015, Oxidative Stress and Its Significant Roles in Neurodegenerative Diseases and Cancer, International Journal of Molecular Sciences, 16(1), 193-217
4. Stadler, K. 2012, Oxidative stress in diabetes, Advances in Experimental Medicine and Biology, Springer International Publishing AG, pp 272-287
5. Esra Birben, Umit Murat Sahiner, Cansin Sackesen, Serpil Erzurum and Omer Kalayci, 2012, Oxidative Stress and Antioxidant Defence, WAO Journal, 5, 9–19
6. Manthey J.A., Buslig B.S and Baker M.E. Eds. 2002, Flavonoids in cell function, Advances in Experimental medicine and Biology, Vol 505, Kluwer Academic/Plenum Publishers, New York.
7. M.G.L Hertog, E.J.M Feskens, D Kromhout, P.C.H Hollman, M.B Katan, 1993, Dietary antioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study, The lancet, 342 (8878), 1007-1011
8. Ock Kyoung Chun, Sang Jin Chung and Won O. Song, 2007, Estimated Dietary Flavonoid Intake and Major Food Sources of U.S. Adults, The Journal of Nutrition, 137, 1244–1252
9. Cao G, Sofic E and Prior R.L., 1996, Antioxidant capacity of tea and common vegetables. Journal of Agricultural and Food Chemistry, 44, 3426 - 3431
10. G. Paganga; N. Miller; C. A. Rice-Evans, 1999, The polyphenolic content of fruit and vegetables and their antioxidant activities. What does a serving constitute? Free Radical Research, 30, 153–162.
11. S. A. Wiseman; D. A. Balentine; B. Frei, 1997, Antioxidants in tea, Critical Reviews in Food Science and Nutrition, 37, 705–718.
12. P. C. H. Hollman; L. B. M. Tijburg; C. S. Yang, 1997, Bioavailability of flavonoids from tea, Critical Reviews in Food Science and Nutrition, 37 (8), 719–738.
13. M. R. Olthof; P. C. Hollman; M. N. Buijsman; J. M. van Amelsvoort; M. B. Katan, 2003, Chlorogenic acid, quercetin-3-rutinoside and black tea phenols are extensively metabolized in humans, Journal of Nutrition, 133 (6), 1806–1814. Erratum in Journal of Nutrition, 2003, 133 (8), 2692.
14. Balz Frei and Jane V. Higdon, 2003, Antioxidant Activity of Tea Polyphenols In Vivo: Evidence from Animal Studies, Journal of Nutrition, 133: 3275S–3284S.
15. Alexander Yashin1, Yakov Yashin, Boris Nemzer, 2011, Determination of Antioxidant Activity in Tea Extracts, and Their Total Antioxidant Content, American Journal of Biomedical Science, 3(4), 322-335
16. Lai Kwok Leung, Yalun Su, Ruoyun Chen, Zesheng Zhang, Yu Huang and Zhen-Yu Chen, 2001, Theaflavins in Black Tea and Catechins in Green Tea Are Equally Effective Antioxidants, Journal of Nutrition, 131, 2248–2251.
17. Yoshino K, Hara Y, Sano, M, Tomita I, 1994, Antioxidative effects of black tea thearubigins and theaflavins on lipid peroxidation of rat liver homogenates induced by tert-butyl hydroperoxide. Biological and Pharmaceutical Bulletin, 17(1), 146-149
18. R Leenen, AJC Roodenburg, LBM Tijburg and SA Wiseman, 2000, A single dose of tea with or without milk increases plasma antioxidant activity in humans, European Journal of Clinical Nutrition 54, 87-92.
19. Yu-Li Lin, Chong-Yurn Cheng, Ya-Ping Lin, Yong-Wei Lau, I-Ming Juan, and Jen-Kun Lin, 1998, Hypolipidemic Effect of Green Tea Leaves through Induction of Antioxidant and Phase II Enzymes Including Superoxide Dismutase, Catalase, and Glutathione S-Transferase, Journal of Agricultural and Food Chemistry, 46 (5), 1893–1899
20. Sarkar, A. and Bhaduri, A., 2001, Black tea is a powerful chemopreventor
21. of reactive oxygen and nitrogen species: comparison with its individual catechin constituents and green tea. Biochemical and Biophysical Research Communications, 284, 173–178.
22. Brown, J. E., Khodr, H., Hider, R. C. and Rice-Evans, C. A., 1998, Structural
23. dependence of flavonoid interactions with Cu2+ ions: implications for their antioxidant properties, Biochemical Journal, 330, 1173–1178.
24. Yang, C. S., Maliakal, P. and Meng, X., 2002, Inhibition of carcinogenesis by tea. Annual Review of Pharmacology and Toxicology, 42, 25–54
Immune Enhancement by Tea and its Anti-Inflammatory Properties
The immune system is the body’s defence against infectious organisms and other toxins and invaders. Through a series of steps referred to as immune response, the immune system attacks the organisms and other toxic substances that invade the body and cause disease. Some of these reactions result in inflammation. Signs of inflammation are heat (rise in body temperature), redness, swelling and pain. Although essential, excessive or prolonged inflammation could damage the human body and increase the risk of Non-Communicable Diseases such as heart disease, stroke and diabetes. Therefore, it is important that inflammation is controlled quickly once the causal agent is eliminated. Further, exposure to environmental toxins and toxicants, such as smoke, dust particles, pesticides, mycotoxins, polychlorinated biphenyls (PCBs) and toxic metals, could also trigger inflammation. As exposure to such agents are common in the present-day environment, anti-inflammatory compounds derived from the diet could play an important role in mitigating the adverse effects of inflammation. Scientific research has found that tea polyphenols possess anti-inflammatory properties. Therefore, tea consumption could mitigate the adverse effects of inflammation, by reducing the risk of Non-Communicable Diseases such as heart disease, stroke and diabetes, where the development of the disease is associated with inflammation. Regular tea consumption could enhance immunity through several mechanisms and may provide protective action against infectious diseases.
Our immune system, what and where it is
We, and other animals, survive in the presence of a myriad of microbes. This diverse group of organisms include yeasts, moulds, fungi, and bacteria. In addition, we are exposed to small organisms such as the malaria parasite and also viruses such as polio, hepatitis, influenza and the common cold, which need to gain entry to our bodies and multiply to cause diseases. Set against this army of potential invaders of the body we, and other warm-blooded animals, have an immune system. Without such a defence we would suffer the fate of a forgotten helping of food left on a plate somewhere in the house. We, like it, would become mouldy and putrid. The immune system is thus essential for survival. It comprises a diverse set of cells scattered throughout the body, some free floating in the blood and lymph and others aggregated in structures such as lymph nodes, spleen and in the wall of the intestine.
If one could assemble all the immune cells in the body in one place, it would make a structure as large as the liver1.
The immune response
The immune response can be sub-divided into two main types; one is the acquired immune response which involves anti-body production and activation of immune cells. Once these cells are exposed to a pathogen, they can ‘remember’ the pathogen and when the same pathogen enters the body again, the response will be much more
efficient. This ‘memory’ phenomenon is the basis of immunisation with vaccines against diseases such as whooping cough, smallpox, yellow fever, polio and cholera.
The other type is the innate immune response. While the acquired response becomes stronger after the first exposure, the innate response has no memory and is generally the same after each exposure to bodily invaders. Innate immune response initiates a process called inflammation, as a response to invasions. The signs of inflammation are heat (rise in body temperature), redness, swelling and pain. Inflammation is also triggered by injury where it is easy to observe these symptoms (e.g. when you cut your finger). These symptoms are brought about by the proliferation and movement of the immune cells, and a series of reactions that initiate in the human body during inflammation. The aim of all these reactions is to destroy the invading pathogens. Therefore, inflammation is an essential function of the human body against such attacks.
Inflammation a Dangerous Friend
The main aim of inflammation is the elimination of invading pathogens. However, some of the mechanisms used to destroy the pathogens could damage human tissues. Therefore, excessive or persistent inflammation could lead to significant damage to the human body, thus becoming a ‘double-edged sword’.2
Not only pathogenic micro-organisms but other factors, such as exposure to polluted air and
cigarette smoke, could also trigger inflammation. ‘Urban fog,’ arising from particulate air pollution, is very common in most urban areas. Inhalation of particulate matter in polluted air could trigger inflammation in the lung, leading to lung diseases. Pesticides and other similar toxicants in the environment and contaminated food may also trigger inflammation. Prolonged inflammation resulting from long exposure to such agents may lead to heart disease and stroke.3, 4
Obesity, which increases the risk of diabetes, is another factor that could trigger inflammation. Further, inflammation diminishes the effectiveness of insulin which controls blood sugar levels, whilst increasing the risk for Type 2 diabetes, the most common form of diabetes5 (see chapter 9 for details on Type 2 diabetes).
During inflammation the energy requirements of the human body increases, as additional energy is required to ‘wage war’ against the invaders. Rather than relying on the diet, the normal source for energy, the body initially derives energy from body constituents. This switch in metabolism ensures that the immune system can become rapidly activated to face the invasion, unrestricted by the uncertainties of the diet. Loss of appetite is a common symptom amongst infected persons. Under these circumstances, muscle and fat tissues are broken down to provide fuel for the immune system. However, loss of tissue cannot go on indefinitely. It is therefore important to restore the appetite of a seriously infected individual to normal by controlling inflammation. Continuous loss of tissue is seen in cancer, where the immune
response is activated by cancer cells. As the source of the stimulation never goes away, the cancer patient becomes grossly emaciated and dies.
Rheumatoid arthritis is a disease caused by the unrestrained growth of the synovial tissue of the joints, resulting in inflammation, pain, and joint damage.6
Although essential to control invading microorganisms, prolonged inflammation increases the risk of developing Non-Communicable Diseases, such as heart disease, stroke and Type 2 diabetes. Conditions which trigger prolonged inflammation such as cancer, rheumatoid arthritis, air pollution and exposure to toxic compounds through other routes also contribute to the further deterioration of the individual’s health condition.
Therefore, it is very clear that inflammation should do its job, mainly destroying the invading pathogens, and then normalcy should be restored in the human body quickly. There are many mechanisms in the human body to minimise the adverse effects of excessive and prolonged inflammation. Foremost among these are the antioxidant molecules in the body, some of which are derived from the diet.7
Anti-Inflammatory Effects 0f Tea
Inflammation induces the production of oxidant molecules in the body, aimed at destroying invading pathogens. (Some of these molecules are similar to the molecules found in bleach used to kill the germs.) Therefore, prolonged inflammation would also lead to prolonged
‘oxidative stress’ (presence of excessive amounts of oxidant molecules), which is a risk factor for most Non-Communicable Diseases. Prolonged oxidative stress also leads to the depletion of antioxidants in the body, as they are used to neutralise oxidants.8 Under these conditions, anti-oxidants derived from the diet could play a significant role in controlling oxidative stress and reducing risk for Non-Communicable Diseases.
Both black and green tea contain very high amounts of antioxidant polyphenols (see chapter 4 for details). Therefore, tea drinking could help to minimise the adverse effects of excessive and prolonged inflammation. Many research studies, conducted to identify the effect of tea on inflammation under various disease conditions, have indicated that tea results in mitigation of adverse effects of inflammation, thus reducing the risk of Non-Communicable Diseases.9
In one such study, 56 obese (obesity triggers inflammation) individuals with high blood pressure were randomly divided into two groups. One group received 379 mg of tea polyphenols, while the other group received a placebo (a substance with no therapeutic effect, used as a control) daily, for three months. Markers (Concentration of certain compounds in blood increase or decrease under inflammation, used to identify the severity of inflammation) for inflammation in blood, were measured at the beginning and the end of the experiment. The group receiving tea polyphenols had significantly lower levels of markers for inflammation at the end of three months.10
Another study examined the association between tea consumption and markers for inflammation, in 6,472 individuals who participated in the 2003–2006 US National Health and Nutrition Examination (NHANES) surveys. It was revealed that tea consumption was positively associated with beneficial bio-markers of cardiovascular disease risk and inflammation.11
A recent review on therapeutic properties of tea against most common environmental toxins and toxicants to humans – smoke, pesticides, mycotoxins, polychlorinated biphenyls (PCBs) and arsenic – concluded that tea provides protective impact in humans against these agents. Protective impact was mainly mediated through antioxidant and anti-inflammatory properties of tea.12
The anti-inflammatory activity of tea, has been further confirmed by a recent systematic review of human clinical trials to identify food items, possessing anti-inflammatory properties. In this, 88 research studies involving large numbers of individuals were reviewed. This review identified and confirmed tea as a food item with antiinflammatory properties. Further, they identified that consumption of tea for more than three months had significant effects.13
Therefore, it could be concluded that tea consumption could mitigate the adverse effects of inflammation, thus reducing the risk of NonCommunicable Diseases.
Tea and immune enhancement
Since ancient times it has been known that there is an array of plants with immune – modulating properties. Medicines containing plant extracts, used in traditional systems such as Aurveda aim at enhancing the natural immune system in the patient and helping him to overcome the disease naturally, rather than acting against the disease.
Exploring diet-health linkages is a major area of modern research, which has identified that plant polyphenols are a class of compounds which enhance immunity. As tea contains uniquely high amounts of polyphenols compared to other plants, many research studies have focused attention on immune enhancing effects of tea. The spread of COVID19 has inspired much research to identify food items that could enhance human immunity. Such research has revealed that EGCG found in both green tea and black tea and TF found in black tea, caffeine and theanine- have immune enhancing properties. Immune enhancement is brought about by modulating complex signalling processes during immune response and enhancing the activity of certain immune cells such as NK cells and T cells. 14
In addition, recent research has demonstrated that tea polyphenols improve immunity by increasing the beneficial micro-organisms in both the gut and the lungs.
Consensus of scientific opinion is that the treatment of viral diseases, including COVID19, should not only start from suppressing the virus itself, but also by improving the body’s immune
system and reducing inflammation. Modern research has shown that tea polyphenols increase probiotics (beneficial micro-organisms) in the gut and lung, reduce pro-inflammatory factors, and improve the body’s immunity. 15
Therefore, regular tea consumption could enhance the immunity and may have prophylactic activity against infectious diseases.
ɇ Immune system is essential for human survival against pathogens and toxic substances. One type of reaction initiated by the activated immune system against pathogens is called inflammation. Excessive and prolonged inflammation could lead to degenerative diseases.
ɇ Anti-inflammatory compounds derived from the diet could mitigate the adverse effects of prolonged inflammation. Research has confirmed that tea polyphenols have antiinflammatory properties and, therefore, tea consumption could alleviate the adverse effects of inflammation.
ɇ Regular tea consumption could enhance immunity and may have protective effects against infectious diseases.
REFERENCES
1. Roitt I., Brostoff J., and Male D. 1993, Immunology, 3rd edition, Mosby
2. Grimble RF. 1990, Nutrition and cytokine action, Nutrition Research Reviews, 3, 193-210.
3. Gabriele Grunig, Leigh M. Marsh, Nafiseh Esmaeil, Katelin Jackson, Terry Gordon, Joan Reibman, Grazyna Kwapiszewska, Sung-Hyun Park, 2014, Perspective: ambient air pollution: inflammatory response and effects on the lung’s vasculature, Pulmonary Circulation, 4(1):25-35.
4. American Heart Association, Air pollution and heart disease, stroke, Available at www.heart.org/en/health-topics/consumerhealthcare/what-is-cardiovascular-disease/air-pollution-and-heart-disease-stroke accessed on 5th September 2022.
5. Steven E. Shoelson, Jongsoon Lee, and Allison B. Goldfine, 2006, Inflammation and insulin resistance, Journal of Clinical Investigation, 116, 1793–1801.
6. Mary Franz, 2014, Nutrition, inflammation and disease, Today’s Dietitian, 16 (2), 44 Available at www.todaysdietitian.com/ newarchives/020314p44.shtml accessed on 5th September 2022
7. Grimble RF, 1994, Nutritional antioxidants and the modulation of inflammation: theory and practice, New Horizons, 2(2), 175-85.
8. Khansari N, Shakiba Y, Mahmoudi M, 2009, Chronic Inflammation and Oxidative Stress as a Major Cause of Age- Related Diseases and Cancer, Recent Patents on Inflammation & Allergy Drug Discovery, 3 (1), 73-80.
9. C. Tangney and H. E. Rasmussen, 2013, Polyphenols, Inflammation, and Cardiovascular Disease, Current Atherosclerosis Reports, 15(5): 324.
10. Bogdanski P, Suliburska J, Szulinska M, Stepien M, Pupek-Musialik D, Jablecka A, 2012, Green tea extract reduces blood pressure, inflammatory biomarkers, and oxidative stress and improves parameters associated with insulin resistance in obese, hypertensive patients, Nutrition Research, 32(6), 421-427.
11. Jacqueline A. Vernarelli and Joshua D. Lambert, 2013, Tea consumption is inversely associated with weight status and other markers for Metabolic Syndrome in U.S. adults. European Journal of Nutrition, 52(3), 1039–1048.
12. Chen L, Mo H, Zhao L, Gao W, Wang S, Cromie MM, Lu C, Wang JS, Shen CL, 2017, Therapeutic properties of green tea against environmental insults, Journal of Nutritional Biochemistry, 40, 1-13.
13. Julissa Luvián-Morales et al, Functional foods modulating inflammation and metabolism in chronic diseases: a systematic review, Critical Reviews in Food Science and Nutrition, 2021 Jan, doi: 10.1080/10408398.2021.1875189.
14. Pritom Chowdhury and Anoop Kumar Barooah, Tea Bioactive Modulate Innate Immunity: In Perception to COVID-19 Pandemic, Frontiers in Immunology, 2020, doi: 10.3389/fimmu.2020.590716
15. Mengyu Hong et al, A Natural Plant Source-Tea Polyphenols, a Potential Drug for Improving Immunity and Combating Virus, Nutrients, 2022, doi.org/10.3390/nu14030550
Antiviral Effects of Tea
Infectious diseases have severely affected humans for centuries. As most viral diseases have no effective drugs yet, properties of naturallyoccurring compounds have been studied for a long time, to ascertain their ability to prevent or minimise the impact of virus diseases. In related research, tea and its constituents have also received attention. Early work has focused on the effects of tea or its components on Influenza A and B, Hepatitis B and C and herpes simplex viruses. Recently, attention has been focused on the possibility of using tea components for prophylaxis, or treatment against COVID19. These studies have strongly indicated that tea components, especially EGCG and theaflavins, have the ability to interfere with the replication process of viruses inside the host. As viral replication increases disease severity, tea has been suggested as a prophylactic agent against viral disease. Further, attention has been focused on developing antiviral drugs from EGCG and theaflavins.
Infectious diseases caused by viruses have seriously threatened human health over centuries. Viruses are responsible not only for acute infections, but also many chronic infectious diseases. Effects of naturally-occurring compounds have been studied for a long time to find their ability to prevent or reduce the effects of diseases caused by viruses. Tea and its components also have been studied for a long time for antiviral effects.
The majority of the early work has focused on the effects of tea, or its components, on Influenza A and B, Hepatitis B and C and herpes simplex viruses. These studies have investigated the possibility of interaction of tea components in the viral infection and replication process. Recently, attention has focused on the possibility of using tea components, especially catechins and theaflavins, as possible candidates for the development of drugs against Severe Acute Respiratory Syndrome Coronavirus 2 (SARSCoV-2), which causes COVID19. Further, using tea as a prophylactic (preventive) measure against COVID19, has also been investigated.
Main Steps in Viral Infection and Replication Process
Viruses cannot replicate and propagate without entering a host cell of an animal or human. Viruses use mechanisms in the host cell for their replication, and then release a large number of newly formed viruses from the infected cell, thus starting a chain of replications in host cells and increasing the severity of the disease. Most antiviral drugs and antiviral compounds found in plants, interfere during the three main stages of viral infection.
Attachment: Viral proteins on the surface of the virus interact with the proteins on the host cell surface and get attached to the host cell. A virus can infect the host cell (animal or human) only if this initial attachment is possible. Therefore, any compound that could interfere with these viral proteins and decrease the possibility of attachment would lower the severity of the disease and become candidates for antiviral drugs.
Replication: After entering the host cell, the virus uses the services of the host cell for replication, producing large number of new viruses inside a single host cell. Any compound that could interfere with the viral replication process will also become a candidate for antiviral drugs. Suppression of replication is generally achieved by interfering with the enzymes involved in the replication process.
Release of newly-formed viruses: Newly-formed viruses have to be released from the host cell and they would repeat the process in other host cells, increasing the severity of the infection. Newly-formed viruses have to break through the host cell membrane to be released. Certain enzymes are required for the cleavage of the host cell membrane. Therefore, compounds that interfere with these enzymes could also be used as antiviral agents.
Research carried out on the antiviral activity of tea, indicates that tea could interfere with the proteins and enzymes involved in the above processes and inhibit viral replication.
Influenza and the common cold are acute infectious diseases of the respiratory tract. Influenza is a severe disease that is highly infectious, which could progress to life-threating diseases such as pneumonia or encephalitis. Influenza infections and common colds spread easily via droplets and contact and, therefore, public prevention and prophylactic measures are important. Experimental studies have reported that tea catechins inhibited influenza viral attachment to human cells, and suppressed replication and neuraminidase activity (neuraminidase is the enzyme responsible for cleaving the host cell membrane and releasing the newly-formed viruses. Suppression of its activity inhibits the release of new viruses and, thereby, lessens the severity of the disease). In addition, these studies have found that tea enhances immunity against viral infections. Several epidemiological studies (studies with large human populations), have suggested that the regular consumption of green tea reduces influenza infection rates and some cold symptoms, and that gargling with tea may protect against the development of influenza infection.1
Although vaccines and several anti-viral hepatitis drugs are available, hepatitis viral infection is still a severe public health issue globally. Therefore, many natural compounds, especially polyphenols and their derivatives, have been studied to find either novel antiviral compounds, or candidates for anti-hepatitis viral drug development. Tea polyphenols also have received attention in these studies, which have highlighted the ability of tea catechins to suppress the initial attachment of
hepatitis B and C virus to the human cells and, thereby, supress the infection. Gallated catechins such as epigallocatechin gallate (EGCG) were more active than the other catechins. Although there is strong evidence that tea polyphenols have anti-hepatitis viral effects, studies have been limited mostly to cell-based or animal-based research. Therefore, confirmation through further clinical trials is required.2
Herpes simplex is a viral disease caused by Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). There is neither a vaccine nor a method to eradicate herpes viruses from the body, but antiviral medications can reduce the frequency, duration and severity of outbreaks. Research has shown that tea catechins demostrate antiviral activity against HSV-1 and HSV-2 and that EGCG possesses greater anti-HSV properties than other tea catechins. Electron microscopy has demonstrated that viruses exposed to EGCG were damaged. Therefore, it was proposed that EGCG could be a promising candidate for developing a micro-biocide to reduce HSV transmission. However, the effectiveness has to be further studied in human clinical trials.3
Effect of Tea on Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) which causes COVID19
SARS-CoV-2 is the virus that causes the coronavirus disease COVID19. As polyphenols in both black and green tea are known to possess antiviral properties, Epigallocatechin Gallate (EGCG), found in both green and black tea, and Theaflavins (TFs), found only in black tea, have
become candidates for recent research on SARSCoV-2.
Several enzymes and proteins responsible for the initial attachment of the SARS-CoV-2 to human cells, have been identified as possible targets for the treatment of COVID19. Initially, through computer-based molecular modelling studies (in silico studies), a large number of plant flavonoids have been studied to find the possible interaction with targets. In these studies, both EGCG and TFs were found to have higher potential for interaction than a large number of other plant compounds used in the study. TFs from black tea were more potent than EGCG. Although these studies indicate the potential of EGCG and TFs against SARS-CoV-2, further research, especially in vivo studies, are required to arrive at firm conclusions.
Results from these in silico studies indicate that EGCG and TFs and, therefore, tea, could be used as a prophylactic (a medicine or course of action used to prevent disease) agent against SARSCoV-2. In these studies, TFs were identified as the molecule with the highest potential to bind with Receptor Binding Domain (RBD) of SARSCoV-2, the virus that causes the disease. This means that TFs have the ability to decrease the initial attachment of the virus with human cells. Therefore, in the absence of an effective drug against SARS-CoV-2, tea could be considered as an alternative prophylactic agent.
Recently a large number of similar studies have been carried out to determine antiviral activity and prophylaxis of tea against viruses, especially
SARS-CoV-2. A review of such studies has shown that the findings of these studies support the use of tea polyphenols as potential candidates in prophylaxis and treatment of COVID-19.4
A recent review of research studies on plant derived food active against respiratory viruses, has identified tea as a food item which is active against respiratory viruses. This review reveals that these food items inhibit different stages of the pathological pathways of respiratory viruses and these alterations eventually lead to the reduction of virus numbers, viral-induced cellular damage and the improved survival of host cells. The authors of this review recommend an increased consumption of these food items, including tea, amongst human populations with a high prevalence of respiratory viral infections, in order to prevent, manage and/or minimise the severity of respiratory virus infections.5
Research carried out so far strongly indicates that tea polyphenols, especially EGCG and TF, have antiviral properties. Evidence suggests
REFERENCES
that tea could be used as a prophylactic agent against viral diseases, including COVID19, and, also, to reduce the severity of the infection.
In addition, these two tea components have received attention as lead compounds (starting compound in drug development), in antiviral drug development.
ɇ Tea polyphenols (EGCG and TFs) have the ability to interfere with viral replication process inside the host.
ɇ It is suggested that tea could be used as a prophylactic against viral disease and to reduce the severity of the disease.
ɇ EGCG and TF have received attention as possible candidates in the development of antiviral drugs.
1. Daisuke Furushima et al, Effect of Tea Catechins on Influenza Infection and the Common Cold with a Focus on Epidemiological/ Clinical Studies, Molecules 2018 20;23(7):1795. doi: 10.3390/molecules23071795.
2. Jae-Min Song, Anti-infective potential of catechins and their derivatives against viral hepatitis, Clinical and Experimental Vaccine Research. 2018 Jan; 7(1): 37–42. doi: 10.7774/cevr.2018.7.1.37
3. J Steinmann et al, Anti-infective properties of epigallocatechin-3-gallate (EGCG), a component of green tea, British Journal of Pharmacology, 2013; 168(5): 1059 – 1073, doi: 10.1111/bph.12009
4. 4. Susmit Mhatre et al, Antiviral activity of green tea and black tea polyphenols in prophylaxis and treatment of COVID-19, Phytomedicine, 2021 May, doi: 10.1016/j.phymed.2020.153286.
5. 5. Francis U. Umeoguaju et al, Plant-Derived Food Grade Substances (PDFGS) Active Against Respiratory Viruses: A Systematic Review of Non-clinical Studies, Frontiers in Nutrition, 2021, Feb, doi: 10.3389/fnut.2021.606782.
Good Brew - Good Taste and Good Health
The preparation of a cup of tea is crucial to deriving the best quality of the tea used. The mportant elements are the quality of the tea and water and the brewing technique. Tea may be selected according to individual preference. To the discerning consumer, the method of harvesting the green leaf and processing of it would be important considerations.
Hand-plucking of the leaf ensures the selection of the most tender leaf and Orthodox processing ensures the retention and enhancement of the inherent natural characteristics of the tea. Orthodox processing also externalizes the subtle variations that exist between different regions and even between different factories in the same region, providing the customer with a wide spectrum of choice.
Water for the brew should be colourless and odourless, soft (pH 6 -8, close to neutral, containing 10-120 mg/L of calcium and magnesium), with a brewing time of 3-5 minutes after being brought to the boil. Reboiled water should not be used and 2.5 g – or a spoonfull – used for a single cup.
Though correct brewing and attention to detail is important to produce a good cup of tea, many tea drinkers, as well as those in the hospitality industry, do not appreciate the importance of correct brewing. Often, incorrect brewing technique, resulting in the reduced extraction of beneficial components, including flavonoids, results in a poor cup of tea despite using quality tea leaf, leading to both loss of taste and health benefits. Essential elements for a good cup of tea are:
ɇ Good quality tea leaf
ɇ Good quality water
ɇ Correct brewing technique
Quality of Tea
The availability of a wide spectrum of tea types enables the consumer to select according to individual preference, from a multiplicity of choices, suitable for different times of the day, or for different occasions. For example, preference may be for a stronger brew in the morning and for a milder brew with delicate aroma for the evening.
The hand-plucking and orthodox processing, primarily employed in Sri Lanka, and the multiplicity of sub-regions, each with variations in tea cultivar type, climate, weather patterns and styles of manufacture, results in different types of tea with subtle differences in taste, aroma, appearance of leaf and liquor and liquoring characteristics, providing a wider choice for the discerning consumer (see chapter 2 for details of different types of tea).
Storage of Tea
As tea is hygroscopic, readily absorbing moisture, as well as odours and fragrances, after opening, tea should be placed in an air-tight container and stored in a cool dry place, protected against heat, light and odours.
Consumers should be mindful of packaging quality when purchasing tea, as the packaging material should meet the necessary protection conditions, preferably through triple lamination. At processing centre level the moisture content of tea is around 3%-4%. As prolonged storage in bulk form and operations such as blending in the open, could result in increasing moisture levels and the consequent deterioration of tea, produce packed at origin generally reaches the customer without any deterioration.
Quality of Water
Primary requirements for water is that it should not contain any matter, dissolved or suspended, which could affect the taste. Obviously the water should be safe for drinking purposes without any toxic material or pathogenic micro-organisms1. Colourless and clear or transparent water without any suspended particles or odour generally indicate suitability.
Water pH
pH indicates the acidity or alkalinity of water. Water with pH closer to neutral (pH = 7) is ideal for the preparation of tea. However, pH range of 6 to 8 would be suitable for brewing tea. High pH or alkaline water tends to darken the colour of the brew, while low pH or acidic water would make the colour lighter.
Chlorinated Water
As chlorinated tap water could affect the taste of tea, ideally, it should not be used for the preparation of tea.
Hardness of water
Hardness of water indicates the amount of dissolved calcium and magnesium in water and excessive amounts will affect the taste and appearance of the brew, even to the extent of depositing a layer of “scum” on the surface of the brew. Water is categorised according to the amount of calcium and magnesium in the following manner. Soft water contains 0-60 mg/L, moderately soft water: 60-120 mg/L, Hard water: 120-180 mg/L, extremely hard water: more than 180 mg/L.
Hard water, containing more than 120 mg/L of calcium and magnesium, is unsuitable for the preparation of tea. However, to get the real taste of tea, the two latter elements are needed in certain proportions and soft water, with 10-120 mg/L of calcium and magnesium would be more suitable for the preparation of tea.
Total dissolved solids (TDS) indicate the dissolved matter in water, including calcium and magnesium. Water with 50-150 mg/L TDS is suitable for brewing tea.
Dissolved Air in Water
Dissolved air in water also contributes to the taste. When water boils dissolved air escapes as bubbles. Therefore, over-boiling of water will
adversely affect the taste of tea. Fresh water just brought to boil is ideal for brewing, whilst using once-boiled water would result in the further reduction of dissolved air, making it unsuitable. Therefore, it is important to use fresh water each time a cup of tea is prepared.
Brewing of Tea
To make a good cup of black tea, approximately 2.5 g (a spoonful of tea) should be used per cup (approximately 220 ml). Tea should be placed in a pre-heated tea pot (tea pot could be pre-heated by swirling warm water) and freshly-boiled water immediately added to the pot, so that the water temperature is between 95-100°C. Three to five minutes, depending on tea particle size, are required to extract all the components which contribute to taste. Larger particles require around five minutes. Shorter brewing times result in inferior tea.
For brewing of green tea, lower water temperature (70-80°C) and shorter brewing durations (2-3 minutes), are adequate. For speciality tea the manufacturer’s recommendations should be followed to obtain the best cup.
Stirring
Stirring enhances the extraction process. Therefore, with black tea, stirring immediately
after pouring the boiling water, then stirring after brewing for one minute and, finally, stirring before serving, results in enhanced extraction and a better cup of tea.
Preparation of a good cup of tea is essential for the enjoyment of drinking tea. Correct brewing ensures that all the components which contribute to the real taste of the tea are extracted in to the cup. Therefore, a good brew ensures both good taste and good health.
ɇ To prepare a good cup of tea, choosing a quality tea is important. When choosing black tea, obtaining a hand plucked, orthodox processed tea, packed at origin, will ensure high quality.
ɇ Colourless and odourless soft water (hardness 10-120 mg/L) with pH 6 to 8 is ideal for brewing tea.
ɇ Fresh water should be just brought to boil and immediately poured (approximately 220 ml) over 2.5 g of black tea in a pot. Three to five minutes should be allowed for brewing with intermittent stirring.
ɇ With green tea brewing, boiled water cooled to 70-80°C for 2-3 minutes will result in a good cup.
REFERENCES
1. Guidelines for drinking water quality, World Health organization, available at, www.who.int/publications/i/item/9789241549950, accessed on 19th August 2022.
How Tea Acquires its Goodness
The quality of tea depends on the chemical composition of the tender shoot, the raw material used in processing. The type of plant or cultivar, agricultural practices, soil type, weather and climate combine to contribute to the chemical composition of the fresh shoot, whilst the processing method and the prevailing conditions also influence the finished product. The taste and aroma of a cup of tea is a composite of all of the above.
As the influential factors vary from country to country, and within each country, often from region to region, tea produced in different countries will vary in character. In countries where the influential factors are uniform throughout, the tea produced will be similarly uniform. In countries where there are distinct variations in elevation, terrain, climate and weather, Sri Lanka for example, the tea produced in each region will have its own distinctive character.
Tea in Sri Lanka is divided into three main growing regions, Upcountry, Mid-country and Low-country, based on elevation above mean sea level (AMSL). Variations within these three main regions result in the production of seven distinct types of tea, known as Nuwara Eliya, Dimbula, Uva, Uda Pussellawa, Kandy, Ruhuna and Sabaragamuwa.
Apart from the intrinsic and natural variability between these regions, the implementation of region-specific agricultural practices and processing methods also play a definitive role in the type of tea produced, thus contributing to a unique and diverse range not found in any other tea-growing country.
Factors That Could Affect the Chemical Composition of Tender Tea Shoots
Many factors could influence the chemical composition of the fresh shoots and, ultimately, determine the quality, taste and aroma of the cup of tea so produced. A thorough knowledge of these factors enable traditional tea producers to make a high quality tea with a distinctive profile to meet a multiplicity of consumers’ preferences around the world.
Factors that mostly affect the quality of the final product:
1. Processing method and conditions
2. Type of tea plant or the variety (cultivar) of tea
3. Agricultural practices
4. Climate and weather
5. Soil
Impact of Processing Method on Tea Quality
Processing method exerts a major influence on the quality of the final product. For example, all types of tea, such as black, green, oolong and white teas are produced from the same raw material, which are the tender shoots of tea plant, whilst the product differentiation is achieved by the variations in processing methods. (see chapter 2 for details on types of tea).
In each of these types of tea, the degree of quality is achieved through fine adjustments in the processing. For example, a longer fermentation period will result in the production of higher
amounts of thearubigins, the reddish brown flavonoid formed during black tea processing. This gives the infusion a deep reddish brown colour and produces a distinct “mouth-feel” when tasted. On the other hand, a shorter fermentation period would result in less thearubigins, yielding a tea with lighter colour and a different taste.
Process adjustments employed to complement the natural character of tea, are relatively easy to implement in “orthodox” processing, with Sri Lanka being best known for the wide range of high quality orthodox tea it produces. A combination of the varying climatic factors in its different tea-growing regions and the fine process adjustments implemented in production enables Sri Lanka to produce a wide range of quality tea, each representative of the region of origin.
Processing may also be adjusted according to season or weather, to produce a tea which is “seasonal” in character. Certain regions such as ‘Dimbulla’ and ‘Uva’ in Sri Lanka are famous for seasonal tea, produced in these regions during dry months, when both relative humidity and ambient temperatures, particularly at night, are low. The right combination of these conditions favour the production of precursors of volatile compounds, enhancing the aroma of the tea. In addition to this natural improvement in aroma, adjustments such as hard wither and shorter fermentation, practiced in these regions during the dry period, result in inhibiting the formation of thearubigins, resulting in a lighter tea with better aroma.1
By fine-tuning the processing method it is possible to either enhance or diminish certain characters of the cup. The orthodox style of processing, which is followed by approximately 98% of factories in Sri Lanka, allows flexibility for such fine-tuning, whilst the CTC style of production, used in India and Kenya, will produce a uniform product with minimal variation. Thus, experienced ‘Tea Makers’ in Sri Lanka are able to produce tea with a variety of characteristics to meet a wide spectrum of consumer preferences, globally.
Effect of the Type of Tea Plant on Chemical Composition
Sometimes there could be distinct variations in the same species of plant, due to inherent variations in the genetic makeup of the plant. Plants with such variations in the same species are identified individually and separately, and the word ‘cultivar’ is used to signify these different plant varieties. Two distinct varieties or cultivars could be identified in tea. The morphology of the plant and the chemical composition of the shoots in these two types could be easily distinguished.
The relatively large and broad leaf type, originally found in Assam, India, is known as ‘Assam type’ (Camellia sinensis var. assamica), whilst the relatively small and narrow leaf type originally found in China, is known as ‘China type’ (Camellia sinensis var. sinensis). Pure Assam type or the China type are rarely found in tea plantations today. Mostly hybrids of these two, with more Assam or Chinese character, are grown depending on the final product planned
for manufacture.2 Plants with Assam character contain more total flavonoids, compared to the China variety and, therefore, are more suitable for black tea production, whilst the China type is preferred for green and oolong tea production. The variations within cultivars permit fine adjustments in a particular type of tea.
A notable example is the planting of broad leaf Assam type in lowland Sri Lanka, where a cup of reddish brown tea with strong mouthfeel is produced. As one travels up from the coastal growing regions, one finds plantations with narrower leaf producing tea of a lighter colour and lower strength; moving to the highest elevations in Nuwara Eliya, one finds plantations with narrow leaf , which produce tea progressively lighter and with distinct aroma. By selecting the cultivar most suitable for a region, or a sub-region, a unique tea may be produced which reflects the most beneficial impact of the conditions specific to that region.
The Tea Research Institute of Sri Lanka has, since the 1960s, been carrying out trials to breed cultivars most suited for the different regions and sub–regions. The recommendations are based
China type
Assam type
on the weather and climatic factors, soil types and likely plant disease profiles particular to that region. Suitability for manufacturing styles, which can and will vary from region to region, are other criteria considered in cultivar selection.
The recommended cultivar list is periodically revised with new and superior cultivars being added subsequent to research. The current list contains 64 cultivars which have been recommended for various tea-growing regions in Sri Lanka.2 Therefore, the unique combination of cultivar characteristics and other contributory factors, such as climate and weather in the specific regions, results in a variety of tea which would be difficult to replicate elsewhere in the tea-growing world.
Impact of Agricultural Practices on the Quality of Tea
The agricultural practices employed have a significant impact on the quality of the final product. Tea made from machine harvested leaf will always be inferior in quality, compared to tea from manually-plucked leaf, as selective harvesting of suitable shoots cannot be achieved with machines. Due to the high cost of manual plucking many tea-producing countries have either entirely, or partially, converted to machine plucking. However, certain tea-producing countries such as Sri Lanka, still use the traditional hand plucking that preserves the superior quality of tea.
Generally, faster growth in the tea bush, due to over-fertilisation, results in a slightly inferior
tea. Therefore, ensuring adequate fertiliser with correct proportions of recommended nutrients, at the correct time, applied under the best conditions, will eventually yield the best quality tea.
Intervals between pruning is another factor that could affect the quality of the tea. Different countries adopt different pruning cycles, depending on the climate/elevation in the country or region. In Sri Lanka the pruning cycle in the cooler up-country region is four years, whilst in the warmer, low-country areas, where growth rate is faster, it is three years. The rate of bush growth is faster in the first two years after pruning, slowing down gradually in the subsequent years. Therefore, the leaf produced in first two years is more suitable for the production of a coloury tea, whilst in the subsequent years, a lighter coloured tea with better aroma could be produced. Experienced managers of plantations use such knowledge to arrange leaf harvests, in order to obtain the most appropriate blend of green leaf, in relation to the required character of the tea.
Effect of Climate and Weather on the Quality of Tea
Climate and weather have a significant effect on the quality of tea produced. Generally, rainy periods are conducive to vigorous growth and a correspondingly inferior tea. Extreme dry conditions generally favour the production of increased amounts of volatile compounds in the leaf, resulting in a tea with better aroma. The general rule is that adverse climatic and weather conditions such as dry periods, warm or cold
temperatures, resulting in stress conditions for the tea plant, enable the production of better quality teas. These phenomena result in the production of ‘seasonal teas’ in certain parts of the world.
The production of well-known ‘Dimbulla’ and ‘Uva’ seasonal teas of Sri Lanka are made possible by the stress exerted on the bushes during dry weather in certain periods of the year. The Dimbulla region experiences dry weather from January to March, or early April, and in the Uva region it is from July to September. Cloudless skies, high daytime temperatures, cold nights and strong winds which desiccate the tender leaves stimulate the production of volatile compounds in the shoot, resulting in the attractive aroma of such seasonal tea.
In Sri Lanka, one sees dramatic changes in climate, weather and vegetation, within a relatively short travel span, such as from the warm, low-country coastal region, to the cooler mountains of the interior. Consequently, in this small island, one finds many regions with distinctively different climate and weather patterns. This wide variation in natural conditions, the enhancement of natural advantages through the selection of cultivars, the implementation of selective agricultural practices as appropriate and the flexibility of the orthodox style of manufacture practiced widely in Sri Lanka enables the production of distinct and varying types of tea unique to each region.
Sri Lanka produces three main types of tea in the low country (below 600 m AMSL), mid country (between 600 to 1200 m AMSL) and up country
(above 1200 m AMSL) regions. However, owing to the differences present within the respective regions, Sri Lanka is able to produce seven distinct categories of tea, known as Nuwara Eliya, Dimbulla, Uva, Uda Pussellawa, Kandy, Ruhuna and Sabaragamuwa. The appearance and taste profiles of these teas vary sharply due to inherent factors, as well as the agricultural and manufacturing practices adopted by experienced planters, which are designed to enhance and complement the natural regional advantages. Similarly, plantations in the same sub-region are able to produce types of tea with subtle differences from each other, through the methods employed in both cultivation and production, assisted by small differences in natural conditions.
Effect of Soil on the Quality
of Tea
Soil fertility and type could also impact cup quality, though to a lesser extent than the other influencing factors, owing to the widespread use of artificial fertiliser. Still, there are subtle differences, such as the distinctive reddishness of the “Bogo Valley” tea, attributed to the high aluminum content in the soil of that region.
Distinct Types of ‘Ceylon Tea’
Sri Lanka has very successfully used natural advantages, enhanced by the specific configuration of agricultural practices and processing methods, to augment the intrinsic quality of tea and to produce many different types of tea, to meet a wide spectrum of consumer preferences worldwide. This has been possible, largely due to wide-ranging climatic differences in the different tea-growing regions of the country.
Distinct qualities of seven major types of Ceylon tea produced in different regions are described below.
Nuwara Eliya Tea
The Nuwara Eliya region is a plateau near the summit of the central highlands of Sri Lanka. The estates in the region are situated at around 1800 m (6000 ft) above mean sea level (AMSL). Mean annual temperature in the region varies between 14 to 16 degrees Celsius during different months of the year and a moderate rainfall is experienced, except from January to March, which is the dry period3. The unique climate and the agricultural and processing practices adopted yield a black tea which could be described as ‘delicately fragrant’.4
The infusion is lighter than all other types of ‘Ceylon tea’. This bright golden liquor with delicate flavor is highly sought after worldwide.
Dimbulla Tea
The Dimbulla region is on the western slope of the central highlands, below the Nuwara Eliya region, and lies between 1,100-1,600 m (3,500-5,000 ft)
AMSL. This region is wet and misty during most parts of the year, as the western slopes directly
meet the southwest monsoon between May and September, supplemented by frequent intermonsoonal rains.
Dimbulla also benefits from the cool, dry winds of the ‘Dimbulla quality season’ that begin in January and continue until March or early April, during which a fine golden-orange coloured, refreshingly mellow cup with a delicate aroma, the Dimbulla seasonal tea, is produced in the region. Variations in topography within the region itself result in different micro-climates, which yield a spectrum of tea with varying quality characteristics, especially aroma.
Uva Tea
The Uva region lies on the eastern slopes of the central highland, southeast of Nuwara Eliya. A greater proportion of the annual rainfall in this region is from the north-east monsoon. It receives some moisture during the south-west monsoon but not to the extent of that of the other tea-growing areas. Therefore, the weather is, overall, much drier than in either Nuwara Eliya, Dimbulla or Boganwatalawa, with less annual mean rainfall than the latter regions. Winds in the region are usually dry, as rains in lower elevations remove the moisture. Therefore, a change of weather lasting a few days can have a noticeable impact on the quality of tea, most pronounced during the ‘Uva quality season,’ from July to September, resulting in the world-famous ‘Uva seasonal teas’. The infusions are reddish brown during wet periods, but change to a lighter golden orange hue during the dry season. The exquisite aroma produced in the seasonal teas attract the attention of connoisseurs of tea world over.
Uda Pussellawa Tea
The Uda Pussellawa region, a relatively small area wedged between Nuwara Eliya and Uva, is located on the eastern slope of the central highlands, below the Nuwara Eliya plateau. Elevations in Uda Pussellawa range from 950 m to 1,600 m (3,000-5,000 ft).
Uda Pussellawa climatic conditions are sharply different from the western slope of the central highland. As with neighbouring Uva, the region receives the bulk of its rain from the northeast monsoon system, between November and January, and the climate is generally similar to that of the Uva region. Udapussellawa experiences dry conditions between June and September, when the south-west monsoonal winds, having deposited rain on the western slopes of the hill country, sweep across Uda Pussellawa. Thus, this region has two quality seasons, from January to March and again from July to September.
Uda Pussellawa teas are described as ‘exquisitely tangy,’ with the liquor, of a pinkish hue, being darker and stronger than the neighbouring Nuwara Eliya tea. Colder conditions at the end of the year add a hint of rose to the bouquet of the tea, known for its medium body and subtle character.
Kandy (or Mid Country) Tea
Kandy lies north of the Nuwara Eliya region and being significantly lower than the southern segment, the region is classified as ‘mid country tea’ (or mid-grown), the elevation ranging from 650 m to 1,300 m (2,000-4,000 ft).
Mostly, the rains arrive during south-west monsoon. The teas produced in the region are stronger and deeper-coloured than those from higher elevations, and are described as strong and full-bodied.
Ruhuna Tea
The Ruhuna tea-growing region lies in the Southern part of the island of Sri Lanka and the terrain consists of coastal plains, with low hills towards the interior, within the ‘wet zone’ of Sri Lanka, receiving its rain mostly from the southwest monsoon. The altitude is 0-600 m (02,000 ft) AMSL, thus the teas are also referred to as ‘Low country (or low grown) tea’. The higher temperatures result in a relatively faster growth of the bush than in the higher elevations.
The cultivars in the region have a pronounced Assam character (broad leaf) and these, combined with highly region-specific climatic factors and processing methods, produce a strong and deep, reddish-brown infusion, with a unique flavour. Generally, the Ruhuna teas have a wider variety of grades, than in higher elevations, and the particle sizes are also relatively larger. Teas with ‘tips’ (tip of the buds) are highly-sought-after grades of Ruhuna teas.
Sabaragamuwa Tea
The Sabaragamuwa region, like Ruhuna, lies in the low country region of the wet zone of Sri Lanka. However most of the estates are at higher elevations than those of Ruhuna, and range from sea level up to around 800 m (2,500 ft). The rains are brought about by the south west monsoon. As the region lies between the coast and the central
highlands, the monsoon blowing inland from the sea brings heavy rains to the region.
The infusion is similar to that of Ruhuna teas, dark yellow-brown with a reddish tint. However, the aroma is different from the Ruhuna tea, with a hint of sweet caramel. Sabaragamuwa teas are described as ‘exceptionally stylish’.
ɇ Quality of the tea is mostly determined by the chemical composition of the shoot plucked for processing. Chemical composition of the fresh shoot is mostly affected by the type of tea plant or cultivar, agricultural practices, climate/weather and soil conditions. Further, processing conditions also influence the character of the final product.
ɇ The type of tea produced varies from country to country and, within each country, there are variations subject to regional and
elvational climate and weather variations, as well as the cultivation and processing methods employed. Such variations, both between countries and within regions, can be quite significant. Sri Lanka is a good example with distinct types of high quality tea, as climate and weather vary significantly within the tea-growing regions. The orthodox style of processing used in Sri Lanka permits further enhancement of the natural character of the tea.
ɇ Sri Lanka produces three main types of tea – up country, mid country and Low country – depending on the elevation. Within these main regions also differences exist, resulting in seven distinct types of tea called Nuwara Eliya, Dimbulla, Uva, Uda Pussellawa, Kandy, Ruhuna and Sabaragamuwa.
REFERENCES
1. R.L. Wickramasinghe, 1978, Facets of tea research in practice, Monograph 7, Tea Research Institute of Sri Lanka.
2. Gunasekare M T K, 2012, Tea plant (Camellia sinensis L.) breeding in Sri Lanka, In: Global Tea Breeding: Achievements, Challenges and Perspectives, (Ed. Liang Chen, Zeno Apostolides, Zong-Mao Chen), Springer-Verlag Berlin Heidelberg, pp125-176.
3. Climate of Sri Lanka, Department of Meteorology, Sri Lanka, available at www.meteo.gov.lk/index.php?option=com_content&view=arti cle&id=94:climate-of-sri-lanka&catid=20&lang=en&Itemid=310 accessed on 19th August 2022.
4. Tea growing regions, Sri Lanka Tea Board. Available at, www.srilankateaboard.lk/index.php/features/the-importance-of-origin, accessed on 19th August 2022
Tea and Diabetes
Diabetes is caused by elevated blood glucose levels. According to the World Health Organization (WHO), global diabetes incidence is increasing and predicted to be the 7th leading cause of death by 2030. Diabetes exists in two forms, namely Type 1 and Type 2, with 90% of Diabetics being afflicted with the latter. The hormone, insulin, controls blood glucose levels; Type 1 is caused by lack of insulin production and Type 2 is caused by a decline in the effectiveness of Insulin.
Research has established that tea consumption could reduce the absorption of glucose from the digestive tract into the body whilst increasing the effectiveness of insulin. These mechanisms would assist in reducing the risk of type 2 diabetes. A review of the population studies assessing the relationship between tea consumption and diabetes risk, has revealed that tea consumption is associated with a reduction in the risk of Type 2 diabetes, which is the most prevalent form of the disease.
Diabetes (Diabetes mellitus) is caused by elevated blood glucose levels. After a meal, as digested food is absorbed into the blood, blood glucose levels increase, inducing the secretion of Insulin. Insulin is the hormone stimulating the liver and muscle cells to absorb glucose, thus reducing blood glucose levels. This mechanism ensures that blood glucose is maintained within certain limits in healthy individuals; a deficiency in this regulatory mechanism leads to diabetes.
Diabetes has become a major global health issue. According to the WHO, the number of people afflicted has risen from 108 million in 1980, to 422 million in 2022. The global prevalence of diabetes among adults over 18 years of age has risen from 4.7% in 1980 to 9.3% in 2022. Diabetes is also a major contributory factor to blindness, kidney failure, heart disease, stroke and may even lead to lower limb amputation. In 2022, an estimated 1.5 million deaths were directly caused by diabetes and another 2.2 million deaths are attributed to high blood glucose. Almost half of all deaths attributable to high blood glucose occur before the age of 70.
Type I Diabetes
Type 1 diabetes (previously known as insulindependent/juvenile or childhood-onset diabetes) is caused by deficient insulin production. Its cause in most cases is not known and it is not preventable with current knowledge. In certain cases it is due to afflictions such as auto–immune diseases that destroy the insulin producing cells in the pancreas. However, by the time the symptoms appear, about 90% of the insulin
producing cells are destroyed and it is too late for corrective measures. Symptoms include excessive excretion of urine (polyuria), thirst (polydipsia), constant hunger, weight loss, vision changes and fatigue. These symptoms may occur suddenly. Type I diabetes patients are only about 10% of the global diabetic community and require daily administration of insulin.
Type 2 Diabetes
Type 2 diabetes (formerly called non-insulindependent or adult-onset diabetes) results from the body’s inability to use insulin effectively. In most cases of type 2 diabetes, the normal level of insulin is produced. However, the glucose absorbing cells do not respond to insulin adequately to take up the required amount of glucose from blood, resulting in the elevation of blood glucose. In some cases insulin production is increased to compensate for the lack of response by the cells and the blood sugar levels would decline to normal levels. In some cases, either increased production is not possible, or the increased insulin production is unable to maintain constant blood glucose levels as the cells do not respond adequately to increased insulin levels.
This extremely heterogeneous disease, comprises approximately 90% of the total diabetes patients globally and in most cases is largely the result of excess body weight and physical inactivity. No single cause is adequate to explain the progression from normal glucose tolerance to diabetes. Symptoms may be similar to those of Type 1 diabetes, but are often less marked. As a result, the disease may be diagnosed several
years after onset, once complications have already arisen. Until recently, Type 2 diabetes was seen only in adults. However, occurrence is increasing in children. This could be due to inappropriate diet and less physical activity resulting in obesity.1
Common Consequences of Diabetes
Over time, diabetes can damage organs in the body such as heart, blood vessels, eyes, kidneys, and nerves. Thus;
ɇ Adults with diabetes have a 2-3-fold increased risk of heart attacks and strokes.
ɇ Combined with reduced blood flow, neuropathy (nerve damage) in the feet increases the chance of foot ulcers, infection and eventual need for limb amputation.
ɇ Diabetic retinopathy is an important cause of blindness, and occurs as a result of long-term accumulated damage to the small blood vessels in the retina of the eye. 2.6% of global blindness can be attributed to diabetes.
ɇ Diabetes is among the leading causes of kidney failure.
Effect of Tea Consumption on Diabetes
A large number of research studies have been carried out to ascertain whether tea consumption could reduce blood glucose levels and the mechanism through which this is effected. Population studies have been carried out using large number of individuals with diabetes and healthy individuals with similar lifestyles as controls, to assess the impact of tea consumption
on diabetes. Additionally, the effect of tea consumption on obesity and weight loss has also been studied as obesity is one of the major contributory factors in diabetes. Inferences from these research studies are discussed below.
Effect of Tea on Blood Glucose Levels
After a meal blood glucose level is increased, as glucose in digested food is absorbed into blood. Although increase of postprandial (occurring after a meal) glucose within certain limits is normal, consistent, dramatic increases of postprandial glucose, due to inappropriate meals and quantities, will increase the risk of diabetes. Therefore, a number of studies have been carried out to find the effect of tea on postprandial blood glucose levels. A review of results of these studies reveal that tea flavonoids have the ability to reduce postprandial blood glucose levels.2
Mechanistic Studies on Tea and Diabetes
Many studies have been carried out to find the mechanisms involved in the reduction of blood glucose levels and diabetic risk by tea consumption. These studies have revealed that tea extends beneficial effects through several different mechanisms.
Effect of Tea on Absorption of Glucose from the Digestive Tract
Molecules in our diet, required for the production of energy and the formation of body structures, are absorbed from the digestive tract and circulated through blood to the body part where it is required. However, most of the large molecules
in our diet cannot be absorbed directly into the blood stream from the digestive tract. The process of digestion breaks them into smaller molecules, which are then absorbed into the blood stream and delivered to the required places. Most of the large carbohydrates in the diet such as starch cannot be directly absorbed. Therefore, large carbohydrate molecules are broken into glucose in the digestion, to facilitate absorption.
Enzymes such as Alpha-amylase and BetaD-glucosidase are involved in the digestion of carbohydrates helping to break large carbohydrates into glucose to facilitate absorption. Many studies, carried out to find the effect of tea on the digestive enzymes, have revealed that tea flavonoids possess the ability to inhibit Alpha-amylase and Beta-D-glucosidase, thus contributing to reduce glucose absorption into blood. This mechanism would be important in controlling blood sugar levels after meals in individuals, who consume carbohydrate rich meals. Anti-diabetic drug Acarbose also functions through the same mechanism.3,4
Tea on the Effectiveness of Insulin
As described above, in Type 2 diabetes, inadequate response to insulin by glucose absorbing cells results in high blood glucose levels. Several research studies have shown that tea flavonoids have the ability to improve the insulin sensitivity of the cells and, thereby, increase the glucose absorption into the cells. Studies carried out to find the mechanisms of action of tea, using animal models, have demonstrated that both black tea and green tea
could increase the glucose uptake by muscle cells and adipocytes (fat storing cells).
Tea increases the binding of insulin to the cells and also enhances the activity of glucose transporters in the cells.5, 6, 7 Seventeen research studies on humans, to find the effect of tea on insulin sensitivity, reviewed recently, have indicated that tea consumption had resulted in reduced fasting blood glucose and glycated hemoglobin levels (Hb A1C, glycated hemoglobin indicates the average blood glucose levels in the past three months). Simultaneously, the fasting insulin levels were also reduced indicating improved insulin activity in the presence of tea.8
Inflammation and Diabetes
Inflammation is the body’s natural response to injury, pathogens and toxins and the first step by the immune system to protect the body from any invader or injury (See chapter 5 for details on inflammation). When the threat is removed, the body reverts to the normal state. However, under some circumstances the immune system could be continuously stimulated, resulting in chronic inflammation. Chronic inflammation could be due to many reasons and obesity is an example. Fatty tissues in the body could send signals to activate the immune system and therefore obesity could lead to chronic inflammation, a risk factor for many Non-Communicable Diseases including diabetes.
Chronic inflammation could, also, result in the reduction of insulin sensitivity and be the main cause of diabetes complications. Therefore,
attenuation of inflammation by tea consumption also contributes to reduce the complications of diabetes.
Obesity
Both overweight and obese individuals have a very high risk of developing Type 2 diabetes. It has been described as the best single predictor of Type 2 diabetes as it is the most important risk factor for diabetes. Almost 90% of people living with Type 2 diabetes are either overweight or obese. Individuals who are overweight, or obese, have added pressure on their body's ability to use insulin to effectively control blood sugar levels, and are therefore more likely to develop diabetes.
In overweight or obese people the cells are stressed as there are more nutrients than the process can handle. This sends a signal to decrease the intake of nutrients into the cell, which works against insulin, whose role is to increase the glucose uptake by the cells. Therefore, overweight and obese people have a higher risk of developing Type 2 diabetes. Further, as fatty tissues constantly send signals to increase the inflammation in the body, overweight and obese people have a higher risk of developing diabetic complications. According to WHO, diabetes could be controlled in a large proportion of diabetes patients merely by controlling the body weight.1
Many research studies have shown that regular tea consumption contributes to weight loss and therefore could contribute to prevention of obesity9. (See chapter 14 for details on weight loss by tea.) Therefore, regular tea consumption could
indirectly contribute to reducing the risk of Type 2 diabetes by preventing obesity.
Population Studies
In 2009, 18 research studies carried out up to 2009 on beverage consumption and diabetes incidence were systematically reviewed. There were 457,922 participants in these studies from diverse populations from different parts of the world, such as Singapore, Puerto Rico, United Kingdom, Finland, United States, Japan, Netherlands and Sweden. The conclusion was that individuals who drank more than 3 to 4 cups of tea per day had an approximate one-fifth lower risk of diabetes than those who did not consume tea.10
Another review had been carried out using thirteen research studies which were performed in Japan, United Kingdom, Finland, Sweden, Germany and Brazil. The objective was to ascertain whether polyphenol rich sources, have an effect on the increase of blood glucose after meals and the insulin levels. Findings reveal that although blood glucose and insulin responses differed depending on the polyphenol–carbohydrate combination, overall, polyphenol sources were shown to reduce the peak and early-phase blood glucose and maintain the blood glucose in the later stages of digestion. Polyphenols were also able to sustain the insulin response. Conclusion of the review was that polyphenols in food and beverages have a beneficial effect on reducing the risk of Type 2 diabetes and black tea was one of the sources of polyphenols.2
Yang and co-workers had carried out a systematic review on the research studies on tea consumption and Type 2 diabetes. A total of 545,517 had participated in these studies. Conclusion of the study was that consumption of tea reduced the risk of Type 2 diabetes. Individuals who consumed two cups of tea per day had a lower risk than those who do not consume tea. Further, those who consumed more than four cups of tea had 15% lower risk.11
A similar systematic review had also established that tea consumption reduces the risk of type 2 diabetes, observing that the consumption of three or more cups of tea was associated with a lower risk. The review considered twelve research studies, six having been conducted in the Unites States and three each in Europe and Asia.12
Effect of Tea on Development of Other Non-Communicable Diseases in Diabetic Patients
Diabetes often leads to the development of other Non-Communicable Diseases, especially heart disease and stroke. Recently, attention had been focused on investigating the ability of tea consumption to reduce the risk of heart disease and stroke in diabetic patients.
In one such clinical trial it was revealed that consumption of a green tea extract for twelve weeks reduced the arterial stiffness, which causes high blood pressure. Authors suggest that tea could be used as an adjunct to the standard therapy to improve arterial stiffness in type 2 diabetes.13
A systematic review has been carried out on the effect of tea on the markers of oxidative stress in diabetic patients. Oxidative stress is a risk factor for heart disease, stroke and cancer. Eight clinical trials with 614 individuals were reviewed and it was found that tea consumption reduced the oxidative stress in these diabetic patients thus reducing the risk of heart disease.14
A similar systematic review to find the effect of green tea extract on the lipid profile of diabetic patients revealed that serum triglyceride and total cholesterol levels were reduced by green tea in diabetic patients lowering the risk of heart disease. These effects were observed in long term green tea consumption.15
These recent reviews indicate that tea consumption not only reduce the risk of diabetes
but also reduce the risk of heart disease and stroke in diabetic patients and improve their quality of life.
Conclusion
Regular consumption of tea could have an effect on Type 2 diabetes (90% of the diabetes is of this type) through several mechanisms. Research reveals that tea consumption could reduce the glucose absorption into the body from the digestive tract, especially from carbohydrate rich food. Tea flavonoids also have the ability to increase the sensitivity of insulin, the hormone which controls blood glucose levels. Further, tea consumption could have indirect effects on diabetes through reduction of inflammation and obesity. These two are the main risk factors for diabetes and also contribute to increases in diabetic complications.
Population studies on tea consumption and risk of diabetes also reveal that tea consumption could reduce the risk of Type 2 diabetes. Recent studies have indicated that tea consumption could also reduce the risk of heart disease and stroke in diabetes patients who are more vulnerable to these diseases.
ɇ Diabetes is caused by elevated blood glucose levels which is mainly caused by either lack of the hormone called insulin, which control the blood sugar levels, or due to reduced effectiveness of insulin, which controls the blood sugar. Diabetes caused due to lack of insulin is called Type 1 diabetes and diabetes due to decreased effectiveness of insulin is called Type 2 diabetes. Approximately 90% of the diabetics suffer from Type 2 diabetes.
ɇ Tea consumption could reduce the risk of diabetes through several mechanisms. Major mechanisms are the reduction of absorption of glucose from the digestive tract and increasing the effectiveness of insulin.
ɇ Regular tea consumption could reduce inflammation and obesity, two main risk factors for diabetes, thus indirectly reducing the risk of diabetes.
ɇ Population studies investigating the association between tea consumption and diabetes risk, indicate that consumption of more than 3 cups of tea per day could reduce the risk of diabetes incidence.
ɇ Recent research indicated that tea consumption could also reduce the risk of heart disease and stroke in diabetes patients who are more vulnerable to these diseases.
REFERENCES
1. Diabetes, Fact Sheet, World Health Organization, available at; www.who.int/mediacentre/factsheets/fs312/en/ accessed on 19th August 2022
2. S. Coe and L. Ryan, 2016, Impact of polyphenol rich sources on acute postprandial glycaemia; A systematic review, Journal of Nutritional Science, 5, 1-11
3. Peluso I and Serafini M, 2016, Antioxidants from black and green tea: from dietary modulation of oxidative stress to pharmacological mechanisms, British Journal of Pharmacology, doi: 10.1111/bph.13649.
4. Williamson G, 2013, Possible effects of dietary polyphenols on sugar absorption and digestion, Molecular Nutrition and Food Research, 57(1), 48-57.
5. Anderson RA, Polansky MM., 2002, Tea enhances insulin activity. Journal of Agricultural and Food Chemistry, 50, 7182–7186.
6. Wu LY, Juan CC, Ho LT, Hsu YP, Hwang LS., 2004, Effect of green tea supplementation on insulin sensitivity in Sprague-Dawley rats. Journal of Agricultural and Food Chemistry, 52, 643–648.
7. Wu LY, Juan CC, Hwang LS, Hsu YP, Ho PH, Ho LT., 2004, Green tea supplementation ameliorates insulin resistance and increases glucose transporter IV content in a fructose-fed rat model, European Journal of Nutrition, 43, 116–24.
8. Liu K, Zhou R, Wang B, Chen K, Shi LY, Zhu JD, Mi MT, 2013, Effect of green tea on glucose control and insulin sensitivity: a metaanalysis of 17 randomized controlled trials, American Journal of Clinical Nutrition, 98(2), 340-348.
9. Kimberly A. Grove and Joshua D. Lambert, 2010, Laboratory, Epidemiological, and human intervention studies show that tea (Camellia sinensis) may be useful in the prevention of obesity, Journal of Nutrition, 140,446–453.
10. Rachel Huxley, Crystal Man Ying Lee, Federica Barzi, Leif Timmermeister, Sebastien Czernichow, Vlado Perkovic, Diederick E. Grobbee, David Batty and Mark Woodward, 2009, Coffee, Decaffeinated Coffee, and Tea Consumption in relation to Incident of Type 2 Diabetes Mellitus, Archives of Internal Medicine, 169(22), 2053-2063
11. Wan-Shui Yang, Wei-Ye Wang, Wen-Yan Fan, Qin Deng and Xin Wang, 2014, Tea consumption and risk of type 2 diabetes: a dose–response meta-analysis of cohort studies, British Journal of Nutrition, 111, 1329–1339
12. Jian Yang, Qun-Xia Mao, Hong-Xia Xu, Xu Ma and Chun-Yu Zeng, 2014, Tea consumption and risk of type 2 diabetes mellitus: a systematic review and meta-analysis update, British Medical Journal, Available at, dx.doi.org/10.1136/bmjopen-2014-005632
13. Patricia Quezada-Fernandez et al, Effect of green tea extract on arterial stiffness, lipid profile and sRAGE in patients with type 2 diabetes mellitus: a randomised, double-blind, placebo-controlled trial, International Journal of Food Science and Nutrition, 2019 Dec;70(8):977-985, doi: 10.1080/09637486.2019.1589430
14. Omid Asbaghi et al, The effect of green tea on C-reactive protein and biomarkers of oxidative stress in patients with type 2 diabetes mellitus: A systematic review and meta-analysis, Complementary Therapies in Medicine, 2019 Oct;46:210-216, doi: 10.1016/j. ctim.2019.08.019
15. Omid Asbaghi et al, Effect of green tea extract on lipid profile in patients with type 2 diabetes mellitus: A systematic review and metaanalysis, Diabetes and Metabolic Syndrome, Jul-Aug 2020;14(4):293-301, doi: 10.1016/j.dsx.2020.03.018
Tea, Cardiovascular Disease and Stroke
Heart disease and stroke are the leading causes of death in the world at present. Narrowing of arteries due to plaque formation restricts the blood supply to the heart and brain. Complete blockage of the already narrowed arteries due to blood clots causes heart attacks and stroke. Several risk factors, which include high cholesterol and fat levels in blood, high blood pressure, diabetes, oxidative stress and inflammation are involved in plaque formation in the arteries. Factors that favour blood clotting increase the risk of heart disease and stroke.
Detailed research on both tea consumption and the above risk factors has revealed that flavonoids in tea have the ability to reduce these risk factors. In addition, epidemiological studies have been carried out in several countries, where large numbers of individuals from populations have been followed for a long period of time. These studies have revealed that regular tea consumption could reduce the risk of heart disease and stroke. As plaque formation is a slow process, taking several years, individuals could adopt healthy lifestyles and diets that reduce the risk. Regular tea consumption could be a part of such healthy diets.
Incidence of Heart Disease
Incidence of Non-Communicable Diseases (NCDs) such as heart disease, stroke, diabetes, high blood pressure and cancer have increased over the years, the rate of increase in the last five years being much higher than previously. According to the World Health Organization (WHO), leading causes of death at present are the NCDs; heart disease is number one with 17.9 million deaths in 2022 and number two is stroke. Improper lifestyle is the main cause for the increased incidence of heart disease and diet is the major contributory factor in our lifestyle that affects health. (See chapter 3 for details on importance of a healthy diet for a healthy life)
Development of Heart Disease
Although there are other forms of heart diseases such as defects in heart valves, increased or decreased heart rate, etc., cardiovascular disease (CVD) is the main cause of death. CVD refers to diseases of the heart (cardio) and blood vessels (vascular). A continuous blood supply to the heart muscle is essential for the continuous pumping of blood by the action of the heart muscle. Coronary arteries supply blood to different parts of the heart, including heart muscles. When there is a blockage in any of these arteries, the blood supply to the heart could be partially or fully interrupted. The place where the blockage occurs (whether in a main artery or a branch artery) and the extent of the blockage will determine the severity of ‘heart attack’. It could be either fatal in the case of a complete blockage in a major coronary artery, or a minor heart attack in the case of a
partial blockage in a branched artery. This type of heart disease is also called coronary heart disease (CHD) and ischemic heart disease. (IHD). Ischemia means inadequate flow of blood to a particular area of body.
Development of heart disease is a gradual process which takes place over many years, through the gradual narrowing of arteries. Healthy arteries are flexible and elastic. With age, arteries could become thick and stiff, known as hardening of arteries or arteriosclerosis, leading to restriction of blood flow. Atherosclerosis refers to the buildup of fats, cholesterol and other substances in and on the artery walls, resulting in plaque formation, which can restrict the blood flow. Atherosclerosis is a specific type of arteriosclerosis, but the terms are often used interchangeably.
Atherogenesis is known as the deposition of fat and cholesterol on the artery walls. However, it is a complex interaction and exchange of material, between the cells of the artery wall and the blood. Messages exchanged between molecules in the blood and cells in the artery wall, also play an important role in atherogenesis. The process starts with the expression or formation of ‘cell adhesion molecules’ on the inner surface of the artery wall, which promote the adhesion of white blood cells to the artery wall, resulting in the promotion of the deposition of fat and the migration of muscle cells, thereby enlarging the area between the endothelium and muscles. Gradually, further depositions, calcification and cell death occur, resulting in plaque formation.
Rupture of the plaque’s protective fibrous cap most commonly causes lethal coronary thrombosis (formation of a blood clot).
Cerebrovascular Diseases (Stroke)
A similar process could take place in the brain, also due to the same risk factors. This could result in partial or complete blockage of blood supply to the brain, resulting in stroke or death. The factors which reduce the risk for heart disease would also reduce the risk of stroke through similar mechanisms.
Risk Factors for Heart Disease
The main factors that influence the expression of adhesion molecules and plaque formation are as follows:
ɇ Elevation of blood cholesterol, triglycerides and fat
ɇ High blood pressure (hypertension)
ɇ Products associated with high blood sugar in diabetes (glycated proteins or lipids)
ɇ Oxidative stress
ɇ Pro-inflammatory cytokines due to inflammation, or derived from excess adipose tissue due to obesity (see chapter 5 for details on inflammation)
Therefore, elevated blood fat, high blood pressure, obesity, oxidative stress, inflammation and diabetes are main risk factors for heart diseases.
Atherogenesis is a slow gradual process that takes place over several years. Generally, by the time of diagnosis, it would have progressed to a critical stage. Therefore, it is important that
healthy individuals should always try to reduce the risk factors, by changing their lifestyles, such as by the regular consumption of food items or beverages that reduce the risk factors. Scientific research carried out in the last few decades indicate that regular consumption of tea could reduce the risk of heart disease. According to these research studies tea could reduce the risk through several mechanisms.
Mechanisms of Risk Reduction by Tea
Lowering of Cholesterol in Blood
Lipids (fat) and cholesterol (a particular type of lipid found in animals) are bound with proteins and form spherical particles for transportation through the blood stream to different parts of the body. These particles are known as lipoproteins. Lipoproteins are grouped according to their density as High Density Lipoproteins (HDL) and Low Density Lipoproteins (LDL). HDL transports cholesterol and lipids from blood to organs whilst LDL transports cholesterol from organs to blood.
High levels of cholesterol in low density lipoproteins (LDL cholesterol) have been identified as a risk factor for heart disease. Therefore, LDL cholesterol is known as ‘bad cholesterol’ whilst cholesterol in high density lipoproteins (HDL cholesterol) are known as ‘good cholesterol,’ as that could remove cholesterol from arteries. Often medical practitioners recommend lipid profile (or lipid panel) test to find the levels of these risk factors in the blood.
Research had shown that tea consumption could reduce blood cholesterol levels, especially the ‘bad
cholesterol’. A systematic review of all research done on tea consumption and blood cholesterol levels have indicated, that black tea1 and green tea2 consumption could reduce the LDL or bad cholesterol levels.
Both black tea3 and green tea4 have the ability to reduce cholesterol absorption from the diet into the blood stream, which contributes to the reduction of cholesterol.
Reduction of Risk by Antioxidants in Tea
Formation of oxidised molecules, particularly oxidation of fat and proteins in the blood stream, increases the risk of their deposition and incorporation into the atherosclerotic plaque. ‘Oxidative stress,’ or high amounts of ‘reactive oxygen species’ (ROS), and ‘free radicals’ (FR) in the body could, therefore, contribute to an increase in the plaque formation in arteries. Antioxidants in tea could neutralise the ROS and FR and reduce the ‘oxidative stress’ in the body, contributing to the reduction of plaque formation in arteries. Oxidation of lipids known as ‘lipid peroxidation’ is an important risk factor for plaque formation in the arteries. Dietary components could have a protective effect on the lipid peroxidation and tea has been identified as one of the dietary components with a protective property.5
Effect of Tea on High Blood Pressure
According to the World Health Organization there are at least 970 million people, worldwide, who have elevated blood pressure (hypertension). Hypertension is a risk factor for coronary heart
disease and the single most important risk factor for stroke. It causes about 50% of ischaemic strokes. Hypertension stresses the blood vessels, causing them to clog or weaken and can lead to atherosclerosis and narrowing of the blood vessels, increasing the likelihood of blocks from blood clots or bits of fatty material, breaking off from the lining of the blood vessel wall. Damage to the arteries can also create weak places that rupture easily. High blood pressure also could contribute to the rupture of the fibrous cap on atherosclerotic plaques, resulting in the formation of clots blocking the blood flow.
Dietary salt is a significant factor in raising blood pressure in people with hypertension and in some people with normal blood pressure. Therefore, salt reduction programmes are carried out in many countries as a measure to reduce heart disease risk. The scientific name for salt is sodium chloride and sodium is the ‘culprit’ for the elevation of blood pressure. As tea is very low in sodium it would be a suitable beverage for the reduction of risk of high blood pressure.
The review of a number of research studies have demonstrated that long-term consumption of black and green tea could significantly reduce blood pressure.6, 7
Endothelial dysfunction is a pathological state of the endothelium (the inner lining of blood vessels) that could lead to high blood pressure and heart disease. With advancing age the proper functioning of the endothelium tends to deteriorate. Endothelial function is a broad function but it mostly affects the constriction
and dilation of blood vessels, which helps in keeping the blood pressure constant. Therefore, endothelial dysfunction could lead to high blood pressure.
Some components in the diet could improve the endothelial function. Flavonoids in tea have been identified as a dietary component that could improve the endothelial function, thereby, reducing the risk of blood pressure and heart disease.8, 9
Effect of Tea on Inflammation
Inflammation is an essential part of the body's healing system. Its aim is to defend the body against bacteria, viruses, and other foreign invaders, to remove debris, and to help repair damaged tissue (see Chapter 5 for details on inflammation). Without inflammation, simple injuries would aggravate and simple infections become deadly. However, inflammation should remove the threat and repair the damage and the body should quickly come back to the normal state.
Prolonged or chronic inflammation could lead to many health issues. Prolonged inflammation could occur due to continuous exposure to pathogenic micro-organisms, such as bacteria, virus and fungi. In addition, exposure to polluted air and obesity could also trigger inflammation. Chronic inflammation is involved in all stages of atherosclerosis, the process that leads to plaque and clogged arteries. Further, inflammation results in oxidative stress, which is another risk factor for heart disease. Therefore, chronic inflammation increases the risk of heart disease and strokes.
As tea contains high amounts of antioxidants, it could reduce the effects of chronic inflammation. Anti-inflammatory compounds have become more important in modern society as exposure to polluted air and number of obese people have increased.
Effect of Tea on Blood Clotting
Blood clots could completely block already narrowed coronary arteries, resulting in a ‘heart attack’. Therefore, often, individuals at risk are prescribed to continually use medicine which reduces the possibility of blood clot formation. Research indicates that tea components have the ability to reduce clot formation in blood to a certain extent. Platelets, a type of cells in blood, are involved in the blood clotting process. Both green tea and black tea have the ability to interfere with the process and reduce the blood clotting.10, 11 This would also contribute to reduce the risk of heart disease.
Effect of Tea on Diabetes
It has been established that diabetes increases the risk of heart diseases. Tea is known to reduce the risk factors for diabetes. Therefore, tea would contribute in the reduction of the risk for heart disease through its ability to reduce the risk of diabetes. Further, high blood sugar results in the attachment of the sugars to other molecules such as lipids and proteins. Such molecules are known as ‘Advanced Glycation End products’ (AGE). Production of AGE has been implicated in the development and progression of many NCDs, including heart disease. Formation of AGE increases the possibility of deposition on the
plaques in arteries, leading to an increase in the stiffness in arteries and oxidative stress, thus contributing to increased risk of heart disease. Tea could interfere with the production of AGE and their oxidation, thereby contributing to the reduction of risk for heart disease due to formation of AGE.12
Population Studies
Results from research on tea and cardiovascular disease, further reinforced by studies on a large number of individuals, have indicated that tea has the ability to reduce the risk for cardiovascular disease through several mechanisms. The ‘Seven countries study’ was the first such large-scale study carried out, over a long period, to establish the relationship between lifestyle factors and coronary heart disease.
Large groups with contrasting lifestyles, eating habits and different risk levels for CHD, were chosen from seven countries, namely, the USA from the American continent, the Netherlands, Finland, Italy, Greece and former Yugoslavia from the European continent and Japan from the Asian continent. Initially, exploratory pilot studies had been carried out in Italy, Spain, South Africa and Japan from 1952 to 1956 and further pilot studies were done from 1956 to 1957 in Finland, Italy, and Greece. The first phase of the seven countries study was from 1958 to 1983 and the second from 1984 to 1999. An important finding of the seven countries study was that flavonoid intake was inversely related to the CHD.13 Tea had been identified as a major source of flavonoid intake.14
Many other similar studies have been carried out later. A review of twenty two such studies have revealed that increased tea consumption is associated with reduced risk of CHD.15
Recent Systematic Reviews on Tea Consumption, Heart Disease and Stroke
Fifty-five research studies of the systematic review of the research carried out so far to determine the effect of polyphenol-rich food and beverages upon micro-vascular function (micro-vascular function is the blood vessel wall components’ structure and function; microvascular dysfunction leads to heart disease and stroke) were included in this review. Findings of the review were that polyphenol-rich food and beverages improve cardiovascular health in healthy individuals, and also in individuals with micro-vascular dysfunction. Tea was identified as a beverage with beneficial effects on microvascular function.16
Another systematic review to find the effect of black tea and green tea on individuals with high blood pressure, in which all research carried out from 1995 to 2019 was reviewed, revealed that regular black tea consumption resulted in the reduction of blood pressure in those individuals. As high blood pressure is directly related to heart disease and stroke, black tea consumption will therefore reduce the risk of heart disease and stroke.17
A systematic review of all population-based research studies carried out up to 2019 with
the aim of finding the relationship between tea consumption and risk of cardiovascular disease and mortality has demonstrated the positive effects of tea. Data from 39 studies were reviewed. The conclusion of the review was that daily tea intake, as part of a healthy habitual dietary pattern, is associated with lower risks of cardiovascular disease and mortality among adults. In addition, it was found that increased tea consumption reduced the risk of stroke also.18
A review of the scientific data obtained from clinical trials published in the last five years, on the role of tea and coffee consumption against cardiovascular diseases (CVDs) and CVD risk factors such as hypertension, hyperglycaemia, and hyperlipidaemia, found that tea consumption reduces some risk factors, especially in overweight people and obese subjects. The authors conclude that results of these clinical trials suggest that tea could exert a protective effects against CVD development. With regard to coffee, the results are controversial and did not allow to draw conclusions.19
The numbers of circulating endothelial progenitor cells have an inverse correlation with chronic smoking and endothelial dysfunction, which are risk factors for heart disease. A human clinical trial has been carried out, to determine the effect of green tea consumption for two weeks on these parameters. Conclusion of the study was that short-term administration of green tea induces a rapid improvement and therefore, green tea consumption may be effective in reducing the risk of future cardiovascular events
in chronic smokers. However, chronic smokers should consider quitting or reducing smoking, rather than drinking green tea as a therapy while continuing to smoke at the same level. 20
Recent population studies and reviews also have confirmed the beneficial effect of tea consumption on stroke.
A population study has been carried out in China using approximately half a million people, to find the relationship between tea consumption and risk of stroke. After ~4.3 million person-years of follow-up (in a long-term follow-up study, each study participant may be followed or observed for several years; one person followed for 5 years will contribute to 5 person-years of follow-up), a dose-dependant positive effect of tea was observed. The authors concluded that higher consumption of tea, especially green tea, was associated with a lower risk of ischemic (ischemia is restriction of blood supply to tissues due to a partial or complete blockage of blood vessels) and haemorrhagic (internal bleeding) stroke. These two are the main causes of stroke. 21
A systematic review on the risk of stroke and food groups had featured eighteen research studies. Conclusion of the review was that these studies provided a high level of evidence, to support the beneficial effect of specific food on stroke outcome. Tea was one of the food items identified as providing beneficial effects. 22
A recently-concluded research study in the UK followed 498,043 men and women, aged 40 to 69 years, for 11.2 years, with the aim of finding
the relationship between black tea drinking (as the UK is a black tea drinking nation) and risk of mortality (death). Special attention was focused on mortality from all cardiovascular disease (CVD), ischemic heart disease, stroke and respiratory disease. Participants were categorised as drinking 1 or fewer, 2 to 3, 4 to 5, 6 to 7, 8 to 9, and 10 or more cups of tea per day. The findings were that there was an inverse association between tea drinking and mortality from all CVD, ischemic heart disease, and stroke. Authors concluded that higher tea intake was associated with lower mortality risk, among those drinking 2 or more cups of tea per day. Further, the authors suggest that tea, even at higher levels of intake, can be part of a healthy diet. 23
These recent systematic reviews, carried on the human clinical trials and population studies clearly indicate that tea consumption could reduce the risk of heart disease and stroke.
Conclusion
A large number of research studies carried out on the effect of tea on heart disease and stroke indicate that flavonoids in tea act through several mechanisms, to reduce the risk of heart disease and stroke. These mechanisms include lowering of blood lipids (fat) by reduced absorption from the digestive tract, and reduction of the oxidation of lipids, by the antioxidant flavonoids in tea, which would reduce their deposition on arteries. Improvement of the endothelial function of the arteries by tea improves the expansion and constriction of the arteries when necessary, thus assisting to maintain constant blood pressure.
Low sodium (or salt) content in tea also makes it a beverage suitable for regular consumption, as high salt intakes could lead to high blood pressure. Reduction of inflammation and blood clotting by tea flavonoids also contribute to reduce the risk of heart disease. Reduction of the risk of diabetes by tea indirectly contributes to the reduction of the risk of heart disease.
Population studies carried out using large populations to determine the risk factors for heart disease also confirm that tea consumption reduces the risk of heart disease.
ɇ Tea could reduce cholesterol levels in blood.
ɇ Tea could reduce blood pressure.
ɇ Tea could reduce oxidative stress which is a risk factor for heart disease and stroke.
ɇ Tea could reduce the risk of diabetes which increases the risk of heart disease and stroke.
ɇ Tea could reduce inflammation which is a risk factor for heart disease and stroke.
ɇ Research studies carried out on large groups of people in several countries have shown that regular tea consumption could reduce the risk of heart disease and stroke.
“Having picked some tea, he drank it, Then he sprouted wings, And flew to a fairy mansion, To escape the emptiness of the world....”
Song Jiaoren, 1882- 1913
REFERENCES
1. Zhao Y, Asimi S, Wu K, Zheng J and Li D, 2015, Black tea consumption and serum cholesterol concentration: Systematic review and meta-analysis of randomized controlled trials, Clinical Nutrition, 34(4), 612-619
2. Onakpoya I, Spencer E, Heneghan C and Thompson M, 2014, The effect of green tea on blood pressure and lipid profile: a systematic review and meta-analysis of randomized clinical trials. Nutrition, Metabolism and Cardiovascular Diseases, 24(8), 823-836.
3. Vermeer MA, Mulder TP and Molhuizen HOJ, 2008, Theaflavins from black tea, especially theaflavin-3-gallate, reduce the incorporation of cholesterol into mixed micelles, Journal of Agricultural and Food Chemistry, 56(24), 12031- 12036.
4. Lisowska A, Stawińska-Witoszyńska B, Bajerska J, Krzyżanowska P, Walkowiak J, 2015, Green tea influences intestinal assimilation of lipids in humans: a pilot study, European Review for Medical and Pharmacological Sciences, 19(2), 209-214.
5. Galassetti P and Pontello A, 2006, Dietary effects on oxidation of low-density lipoprotein and atherogenesis, Current Atherosclerotic Reports; 8(6), 523-529.
6. Liu G, Mi XN, Zheng XX, Xu YL, Lu J and Huang XH, 2014, Effects of tea intake on blood pressure: a meta-analysis of randomised controlled trials, British Journal of Nutrition, 112(7), 1043-1054.
7. Yarmolinsky J, Gon G and Edwards P, 2015, Effect of tea on blood pressure for secondary prevention of cardiovascular disease: a systematic review and meta-analysis of randomized controlled trials, Nutrition Reviews, 73(4), 236-246.
8. Schreuder TH, Eijsvogels TM, Greyling A, Draijer R, Hopman MT and Thijssen DH, 2014, Effect of black tea consumption on brachial artery flow-mediated dilation and ischaemia-reperfusion in humans, Applied Physiology, Nutrition and Metabolism, 39(2), 145-151.
9. Grassi D, Desideri G, Di Giosia P, De Feo M, Fellini E, Cheli P, Ferri L and Ferri C, 2013, Tea, flavonoids, and cardiovascular health: endothelial protection, American Journal of Clinical Nutrition, 98(6 Suppl), 1660S-1666S.
10. Steptoe A, Gibson EL, Vuononvirta R, Hamer M, Wardle J, Rycroft JA, Martin JF and Erusalimsky JD, 2007, The effects of chronic tea intake on platelet activation and inflammation: a double-blind placebo controlled trial, Atherosclerosis, 193(2), 277-282.
11. Chen XQ, Wang XB, Guan RF, Tu J, Gong ZH, Zheng N, Yang JH, Zhang YY, Ying MM, 2013, Blood anticoagulation and antiplatelet activity of green tea epigallocatechin (EGC), Food and Function, 4(10), 1521- 1525
12. Nakagawa T, Yokozawa T, Terasawa K, Shu S and Juneja LR, 2002, Protective activity of green tea against free radical- and glucosemediated protein damage, Journal of Agricultural and Food Chemistry, 50(8), 2418-2422.
13. Hertog MG, Kromhout D, Aravanis C, Blackburn H, Buzina R, Fidanza F, Giampaoli S, Jansen A, Menotti A, Nedeljkovic S et al, 1995, Flavonoid intake and long-term risk of coronary heart disease and cancer in the seven countries study, Archives of Internal Medicine, 155(4), 381-386.
14. Cook, N.C. and Samman, S., 1996, Flavonoids—Chemistry, metabolism, cardioprotective effects, and dietary sources, The Journal of Nutritional Biochemistry, 7 (2), 66-76
15. Zhang C, Qin YY, Wei X, Yu FF, Zhou YH and He J, 2015, Tea consumption and risk of cardiovascular outcomes and total mortality: a systematic review and meta-analysis of prospective observational studies, European Journal of Epidemiology, 30(2), 103-113.
16. Kirsty A. Woodward et al, Polyphenols and Microvascular Function in Humans: A Systematic Review, Current Pharmaceutical Design, 2018;24(2):203-226, doi: 10.2174/1381612823666171109103939
17. Marjan Mahdavi-Roshan et al, The effects of regular consumption of green or black tea beverage on blood pressure in those with elevated blood pressure or hypertension: A systematic review and meta-analysis, Complementary Therapies in Medicine, 2020 Jun;51:102430, doi: 10.1016/j.ctim.2020.102430
18. Mei Chung et al, Dose–Response Relation between Tea Consumption and Risk of Cardiovascular Disease and All-Cause Mortality: A Systematic Review and Meta-Analysis of Population-Based Studies, Advances in Nutrition, 2020 Jul 1;11(4):790-814, doi: 10.1093/ advances/nmaa010
19. Arianna Di Lorenzo et al, Effects of Tea and Coffee Consumption on Cardiovascular Diseases and Relative Risk Factors: An Update, Current Pharmaceutical Design, 2017;23(17):2474-2487, doi: 10.2174/1381612823666170215145855
20. Weon Kim et al, Effect of Green Tea Consumption on Endothelial Function and Circulating Endothelial Progenitor Cells in Chronic Smokers, Circulation Journal, 2006 Aug;70(8):1052-7, doi: 10.1253/circj.70.1052
21. Tian Tian et al, Tea consumption and risk of stroke in Chinese adults: a prospective cohort study of 0.5 million men and women, American Journal of Clinical Nutrition, 2020 Jan 1;111(1):197-206, doi: 10.1093/ajcn/nqz274
22. Cuiyu Deng et al, Stroke and food groups: an overview of systematic reviews and meta-analyses, Public Health Nutrition, 2018 Mar;21(4):766-776, doi: 10.1017/S1368980017003093
23. Maki Inoue-Choi et al, Tea Consumption and All-Cause and Cause-Specific Mortality in the UK Biobank, Annals of Internal medicine, 2022. https://doi.org/10.7326/M22-0041
Tea and Cancer
Cells are the smallest units or building blocks of tissues and organs in the human body. Alterations in the cells could result in abnormal cells with uncontrolled proliferation resulting in the formation of cancerous tissue. Alterations in the cells are initiated by damage to DNA in the cells which control all cellular processes. The damage is usually caused by carcinogenic substances or harmful radiation, such as UV light. Research has demonstrated that flavonoids in tea have the ability to neutralise cancer causing substances and reduce the risk of cancer initiation. Once cancer is initiated in a cell, it is developed into a malignant cancerous tissue through several stages. Research also has shown that tea flavonoids could interfere with this process through several mechanisms, and reduce the risk of formation of a malignant cancer.
Metastasis is the process where cells from a malignant cancer migrate to other parts of the body, through the blood circulatory system and establish a cancer in another part of the body. Metastasis greatly reduces the effectiveness of conventional cancer therapy. Research has also shown that tea flavonoids reduce the risk of metastasis. In addition, a review of a large number of population studies, where cancer patients and healthy individuals with similar lifestyles were compared to find the factors that influence the carcinogenesis process, has revealed that tea consumption reduces the risk of cancer.
What is Cancer?
All tissues or organs in the human body are made from microscopic units called cells, found in trillions, which could be considered as the smallest building blocks in the human body. A process of replacing old and damaged cells would continuously take place in the human body, through the proliferation of existing cells. The size of the tissues and organs in adults are kept constant, by the production of only an adequate number of cells to replace the dead and damaged cells. Alterations in normal cells could produce abnormal cells with excessive and unlimited proliferation. This results in the formation of an invasive cancerous tissue.
Development of cancer, or ‘carcinogenesis,’ is a process with multiple stages. Research has shown that some components in the tea brew, especially flavonoids, could interfere in all these stages to reduce the risk of development of cancer.
Cancer Initiation
What causes the normal cells to lose its control and become uncontrollably proliferating cancer cells?
All the cellular processes are controlled by the genetic material known as DNA, present in all the cells. Alterations in DNA, called “mutation,” is the starting point in cancer development. Mutations could occur naturally in the cells and most altered cells merely die. However, in some cells, natural repair mechanisms could repair the damaged DNA. Therefore, all mutations or damage caused to DNA do not necessarily lead to cancer.
But there is a possibility that some of the altered cells could become cancerous cells, although only a very minute fraction of mutations would lead to cancer. As mutations or damage to DNA is the starting point in the carcinogenesis process, mutations could be considered as a risk factor for cancer.
Some of the risk factors leading to cancer, such as family history and advancing age, cannot be controlled by individuals. However, there are many other risk factors, such as exposure to cancer causing substances, radiation, sunlight and polluted air (including smoking), which could be controlled by the individual. Inappropriate diet, alcohol use, chronic inflammation, infectious agents and obesity also could increase the cancer risk. Therefore, adding items such as tea, which have the potential to reduce the risk of cancer, to the list of regularly consumed dietary items would be advantageous to any individual.
Cancer-Causing Substances
Certain chemical substances, known as mutagens, have the ability to damage the DNA. Some mutagenic substances are more likely to cause cancer than other mutagens. Substances most likely to cause cancer are called as carcinogens. Humans could be exposed to such carcinogens through the diet, inhalation or through skin. In addition, exposure to certain radiations such as UV in sunlight could also cause cancer. A list of carcinogens in the environment has been prepared and made available at the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO).1 However,
it does not mean that these substance will necessarily cause cancer.
Many factors determine whether a person exposed to a carcinogen will develop cancer. The individual’s genetic background and the degree and duration of exposure has a great influence on cancer development. Therefore, individuals should always try to limit exposure to carcinogens. This is possible in the case of voluntary exposures such as smoking. Individuals involved in certain industries could also have a higher risk and, at present, regulations are in place in most countries to control workplace exposure to carcinogens. However, it is difficult to control involuntary exposures from the environment.
Once carcinogens enter the human body there are mechanisms to convert them into water soluble forms and excrete them with urine from the body. Liver enzymes play the main role in this detoxification process. Kidneys act to excrete the detoxified substances with urine.
Certain dietary components could also directly interact with carcinogens and convert them to harmless or less harmful substances. Further, some dietary components could also assist the natural detoxification processes by increasing the rate of detoxification.
Inhibition of Mutagenic Activity of Carcinogenic Substances by Tea
Several research studies have shown that both black tea and green tea polyphenols have the ability to reduce the carcinogenicity of known carcinogens, such as N-Methyl-N′-nitro-N-
nitrosoguanidine (MNNG) and Nicotine-derived nitrosamine ketone (NNK) and several other carcinogens, through anti-mutagenic activity. Oxidation of carcinogenic molecules inside the body could make them more potent carcinogens. Research has also shown that the antioxidant activity of tea flavonoids play an important role in inhibiting the formation of such oxidised carcinogens.2 ‘Oxidative stress’ could increase the production of highly reactive ‘Free Radicals’ (FR) and ‘Reactive Oxygen Species” (ROS) in the human body. FR and ROS could also react with DNA and cause mutations. Therefore, antioxidant flavonoids in tea could play a role in reducing the risk of cancer, by neutralising the FR and ROS (see chapter 4 for details on antioxidant activity of tea).
Further, tea flavonoids have the ability to induce and improve the activity of detoxifying enzymes in the liver. Cytochrome P 450 (CYP 450) and glutathione-s–transferase (GST), are examples for such enzymes. Research studies have shown that tea flavonoids have the ability to induce and improve the activity of such enzymes, thus reducing the risk of cancer.3
Progression of Cancer
Once a normal cell is altered through mutation, it exchanges signals, a process known as signal transduction. This signal transduction is a complicated process which eventually helps in the progression of the mutated cell into a cancerous tissue. A number of studies have shown that tea flavonoids could interfere with signal transduction pathways and reduce cancer promotion.4
Programmed Cell Death (Apoptosis)
A process called programmed cell death, or apoptosis, takes place in multicellular organisms. This is different from necrosis. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins or trauma, which promotes the unregulated digestion of cell components, resulting in cell death. In contrast, apoptosis is a naturally occurring, programmed and targeted, cause of cellular death. Apoptosis is a highly regulated process. While apoptosis often provides beneficial effects to the organism, necrosis is almost always detrimental to the organism.
Apoptosis helps in the destruction of cancer cells too. A number of research studies have shown that tea flavonoids induce the apoptosis in cancer cells and thereby help in the destruction of cancer cells.5
Angiogenesis
Angiogenesis, an important process in growth and development and in wound healing, is the development of new blood vessels from preexisting blood vessels. However, angiogenesis also helps to convert benign tumor to a malignant tumor. New blood vessels formed through angiogenesis would keep on providing nutrients and other essential ingredients, which are required for the proliferation of the cancerous tissue. Therefore, anti-angiogenic substances could be used in cancer therapy to reduce tumor growth. Research has shown that both green tea components, such as epigallocatehcin gallate (EGCG) and black tea components, such as theaflavin (TF), have the ability to inhibit cancer growth through anti-angiogenic properties.6, 7
Growth Factors
Growth factors which are naturally produced in living organisms promote growth and proliferation of cells. Although important in normal growth and development, growth and proliferation of cancer cells are also promoted by the same factors. Therefore, suppression of growth factors is one aspect considered in cancer therapy. Research has shown that tea flavonoids could assist in reducing cancer growth by inhibiting the activity of growth factors.8
Metastasis
Metastasis is the spread of cancer from one part of the body, to another part which is not directly connected. Some cancer cells acquire the ability to penetrate walls of blood vessels, enabling these cells to migrate to other parts of the body through the blood circulatory system. After reaching another site, the cancer cells could re-penetrate the blood vessel wall and establish a secondary tumor in a different site in the body. The possibilities of curative treatment is greatly reduced when a cancer is metastasised. Therefore, any agents that could suppress metastasis of cancer would be important in cancer therapy. Research studies have shown that both black tea (theaflavins) and green tea (EGCG) flavonoids have cancer metastasis suppressing properties.9, 10
Population Studies on Cancer Incidence
As shown above, a large amount of research has been carried out on the mechanisms of carcinogenesis, demonstrating that tea components, especially flavonoids, have the ability to reduce the risk of cancer. In epidemiological or population studies, factors that affect the development of a disease is studied across a very large number of groups of people. Generally, patients are compared with controls who are healthy individuals with a similar lifestyle. Results from similar studies could be pooled together in a ‘systematic review’ to get a better understanding of factors that influence the risk of causing a disease. Systematic reviews of a number of population studies also have revealed, that tea consumption could reduce the risk of cancer in many different sites of the human body.
Tea Consumption and Thyroid Cancer
The association between tea consumption and thyroid cancer has been evaluated in a number of research studies. A systematic review of fourteen such studies, covering 106,447 individuals, which included 2955 thyroid cancer patients, had revealed that higher tea consumption has a protective effect.11 The effects were significant in the studies carried out in Europe and America, while the effect was not significant in the studies done in Asia, probably due to the limited number of studies (3) and the low number of patients (366) included in those studies.
Tea Consumption and Gall Bladder Cancer
A systematic review of the research on gall bladder cancer has revealed that tea consumption reduced the risk of gall bladder cancer in women. These studies involved a total of 753 patients and a total of 115,349 participants.12
Tea Consumption and Oral Cancer
Results from twenty research studies on tea consumption and the risk of oral cancer has been reviewed recently. A total of 11,984 patients had been involved in these research studies, along with healthy individuals with similar lifestyles, for comparison. Findings of this review concluded that tea consumption was associated with decreased risk of oral cancer.13
Tea Consumption and Lung Cancer
Research results from thirty-eight research studies on lung cancer had been systematically reviewed, where 59,041 lung cancer patients and 396,664 healthy individuals, were used as controls for comparison. Conclusion of this review was that both green tea and black tea consumption were significantly associated with reduced risk for lung cancer.14
Enhancement of Conventional Cancer Therapy by Tea Flavonoids
A number of research studies have been carried out, to evaluate the effect of tea flavonoids on cancer patients while they are undergoing conventional cancer therapy. The aim of most of these studies was to find whether tea flavonoids,
with their anti-inflammatory and anti-oxidant properties, could ameliorate the deleterious effects of chemotherapy and radiotherapy. Systematic review of such research studies have revealed that epigallocatechin gallate (EGCG), the major flavanol in tea, not only ameliorated the deleterious effect of conventional therapy but also enhanced the effect of the therapy through additive or synergistic effects.15
Recent Systematic Reviews on Tea Consumption and Cancer
Recently, many systematic reviews have been carried out using human clinical trials and population studies to find the effect of tea consumption on cancer. These studies pool the results from similar research done by independent laboratories around the world on the effect of tea consumption on cancers, with the aim of forming an opinion based on data from all the studies. The studies generated clear evidence and conclusions on the effect of tea consumption on all types of cancer. Results from a few of these recent reviews are discussed below.
Data was pooled from thirteen studies to find the effect of tea consumption on gastric cancer. Findings indicated that drinking tea has a preventive effect on the risk of gastric cancer. They found that there is a relationship between the amount of tea consumed and the duration of tea consumption with the reduction of risk. The highest dose studied was six cups of tea and the longest duration was twenty-five years. This group of consumers had the best effect.16
A review of ten research studies on the effect of tea on prostate cancer revealed that tea consumption was associated with a reduced risk of prostate cancer. In this study also, it was found that consumption of more tea resulted in a better risk reduction.17
Research studies on tea consumption and breast cancer, the most common cancer in women, also has been reviewed recently. It was revealed from pooled data that there is a potential protective effect of tea consumption on breast cancer. Recurrence after successful treatment is one of the issues in breast cancer. Interestingly, tea consumption was more effective in reducing the risk of recurrence of breast cancer.18
The biliary tract includes the gallbladder and bile ducts inside and outside the liver. These are also called the biliary system, the organs and ducts that make and store bile. Research studies carried out from 2016 on the effect of tea consumption on biliary tract cancer has been systematically reviewed. The findings were that there is an inverse relationship between tea intake and risk of biliary tract cancer. Furthermore, dose response analysis indicated that the risk of biliary tract cancer decreased by 4% with each additional cup of tea consumed per day.19
Ovarian cancer accounts only for 4% of female cancers worldwide. However, as prognosis (likely outcome) of ovarian cancer is unfavourable, risk reduction has received more attention. A review of fourteen studies resulted in the conclusion that ovarian cancer risk decreased as the consumption levels of tea increased.20
Review of research carried out in the last ten years on nasopharyngeal cancer (upper part of the throat behind nose) and tea consumption, concluded that habitual tea consumption could be associated with the reduction of the risk of nasopharyngeal cancer development.21
A type of cancer that originates in the lymphatic system is known as non-Hodgkin’s lymphoma. Review of research studies on the link between tea and non-Hodgkin’s lymphoma concluded that green tea intake may be associated with reduced risk of non-Hodgkin’s lymphoma.22
Myelodysplastic syndromes is a group of cancers that prevent maturation of blood cells in the bone marrow. Review of thirteen research studies carried out between 2001 and 2017 revealed that tea consumption was associated with reduced risk of Myelodysplastic syndrome.23
These recent reviews on research carried out to find the effect of tea consumption on the cancer in different sites of the body clearly indicate that tea could reduce the risk of these cancers. Regular tea consumption for long periods was associated with higher reduction of the risk.
Conclusion
Results from a very large number of research studies on tea and cancer indicate that certain components in the tea brew, especially flavonoids found in both black tea and green tea, act through several different mechanisms to reduce the risk of cancer. Tea flavonoids are helpful in all the stages of the cancer development process. Further, a large number of studies have been carried out, to
ascertain the effect of tea consumption on cancer in different parts of the human body using cancer patients and healthy individuals with a similar lifestyle, as control. These studies also indicate that tea consumption reduces the risk of cancer in different parts of the human body.
ɇ Cancer is initiated by damage to the DNA in a cell by carcinogenic substances. Tea flavonoids have the ability to bind and neutralise most common carcinogens and reduce the risk of cancer.
ɇ Once a cancer is initiated in a cell, it is developed into a large malignant cancerous tissue through a complicated process which occurs through several stages. Tea flavonoids have the ability to interfere in this process through several mechanisms and reduce the risk of development of malignant cancerous tissue.
ɇ Metastasis is the process where cancer cells from one site in the body migrate to another part of the body, through the blood circulatory system and establish a new cancer. Metastasis greatly reduces the effectiveness of conventional cancer therapy. Tea flavonoids have the ability to reduce the metastasis process.
ɇ A large number of population studies in which large number of patients were compared with healthy individuals, to ascertain factors that influence cancer, have shown that tea consumption reduces the risk of cancer.
REFERENCES
1. IARC monographs on the evaluation of carcinogenic risks to humans. Available at monographs.iarc.fr/ENG/Classification/ Accessed on 21st August 2022
2. Brahma N. Singh, Prateeksha, A.K.S. Rawat, R.M. Bhagat and B.R. Singh, 2015, Black Tea: Phytochemicals, Cancer Chemoprevention and Clinical Studies, Critical Reviews in Food Science and Nutrition, dx.doi.org/10.1080/10408398.2014.994700
3. P. Srinivasan, S. Suchalatha, P. V. A. Babu et al, 2008, Chemopreventive and therapeutic modulation of green tea polyphenols on drug metabolizing enzymes in 4-nitroquinoline 1-oxide induced oral cancer, Chemico-Biological Interactions, 172(3), 224–234.
4. Rahmani AH, Al Shabrmi FM, Allemailem KS, Aly SM, Khan MA, 2015, Implications of Green Tea and Its Constituents in the Prevention of Cancer via the Modulation of Cell Signalling Pathway, Biomed Research International, doi: 10.1155/2015/925640
5. V. S. Thakur, K. Gupta, and S. Gupta, 2012, Green tea polyphenols causes cell cycle arrest and apoptosis in prostate cancer cells by suppressing class I histone deacetylases, Carcinogenesis, 33(2), 377–384.
6. Morbidelli L, 2016, Polyphenol-based nutraceuticals for the control of angiogenesis: Analysis of the critical issues for human use, Pharmacological Research, 111, 384-393.
7. Gao Y, Rankin GO, Tu Y and Chen YC, 2016, Inhibitory Effects of the Four Main Theaflavin Derivatives Found in Black Tea on Ovarian Cancer Cells, Anticancer Research, 36(2), 643-651.
8. Pabla B, Bissonnette M and Konda VJ, 2015, Colon cancer and the epidermal growth factor receptor: Current treatment paradigms, the importance of diet, and the role of chemoprevention, World Journal of Clinical oncology, 6(5), 133-141.
9. Jianping Shao, Qingyan Meng, Yongyuan Li, 2016, Theaflavins suppress tumor growth and metastasis via the blockage of the STAT3 pathway in hepatocellular carcinoma, Journal of Onco Targets and therapy, 9, 4265-4275.
10. Maruyama T, Murata S, Nakayama K, Sano N, Ogawa K, Nowatari T, Tamura T, Nozaki R, Fukunaga K, Ohkohchi N, 2014, (-)-Epigallocatechin-3-gallate suppresses liver metastasis of human colorectal cancer, Oncology Reports, 31(2), 625-633.
11. Sugang Ma, Chunyan Wang, Jiandong Bai, Xipeng Wang, Chuandong Li, 2015, Association of tea consumption and the risk of thyroid cancer: a meta-analysis, International Journal of Clinical and Experimental Medicine, 8(8), 14345-14351
12. Guangwei Zhu, Jin Hua, Zhijian Wang, Feifei She and Yanling Chen, 2015, Tea consumption and risk of gallbladder cancer: A metaanalysis of epidemiological studies, Molecular and clinical oncology, 3, 613-618.
13. Zhang W, Geng T, Han W and Dou H, 2014, Tea intake and risk of oral, pharyngeal, and laryngeal carcinoma: a meta-analysis, Medical Science Monitor, 20, 2142-2150.
14. Wang L, Zhang X, Liu J, Shen L and Li Z, 2014, Tea consumption and lung cancer risk: a meta-analysis of case-control and cohort studies, Nutrition, 30(10), 1122-1127.
15. Lecumberri E, Dupertuis YM, Miralbell R and Pichard C, 2013, Green tea polyphenol epigallocatechin-3-gallate (EGCG) as adjuvant in cancer therapy, Clinical Nutrition, 32(6), 894-903.
16. Yanhong Huang et al, Association between green tea intake and risk of gastric cancer: a systematic review and dose-response metaanalysis of observational studies, Public Health Nutrition, 2017 Dec;20(17):3183-3192, doi: 10.1017/S1368980017002208
17. Yuming Guo et al, Green tea and the risk of prostate cancer: A systematic review and meta-analysis, Medicine (Baltimore), 2017 Mar;96(13):e6426, doi: 10.1097/MD.0000000000006426
18. Vincenza Gianfredi et al, Green Tea Consumption and Risk of Breast Cancerand Recurrence—A Systematic Review and Meta-Analysis of Observational Studies Nutrients, 2018 Dec 3;10(12):1886, doi: 10.3390/nu10121886
19. Jianping Xiong et al, Tea consumption and the risk of biliary tract cancer: a systematic review and dose-response meta-analysis of observational studies, Oncotarget, 2017 Jun 13;8(24):39649-39657, doi: 10.18632/oncotarget.16963
20. Dongyu Zhang et al, Non-herbal tea consumption and ovarian cancer risk: a systematic review and meta-analysis of observational epidemiologic studies with indirect comparison and dose–response analysis Carcinogenesis, 2018 May 28;39(6):808-818, doi: 10.1093/ carcin/bgy048
21. Simon I Okekpa et al, The Association between Tea Consumption and Nasopharyngeal Cancer: A Systematic Review and MetaAnalysis, Asian Pacific Journal of Cancer Prevention, 2020 Aug 1;21(8):2183-2187, doi: 10.31557/APJCP.2020.21.8.2183
22. Hanifeh Mirtavoos-Mahyari et al, Effects of Coffee, Black Tea and Green Tea Consumption on the Risk of Non-Hodgkin’s Lymphoma: A Systematic Review and Dose–Response Meta-Analysis of Observational Studies Nutrition and Cancer, 2019;71(6):887-897, doi: 10.1080/01635581.2019.1595055
23. Marina R Sweeney et al, Medical Conditions and Modifiable Risk Factors for Myelodysplastic Syndrome: A Systematic Review, Cancer Epidemiology, Biomarkers and Prevention, 2019 Sep;28(9):1502-1517, doi: 10.1158/1055-9965.EPI-19-0106
Effect of Tea Consumption on Oral and Digestive Tract Health
The human digestive tract consists of the oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine and other related organs that work together to convert food through the digestion process into basic nutrients for absorption by the body. Large populations of microorganisms live in all parts of the digestive tract, some harmful and others beneficial to the human body. ‘Commensal microorganisms’ that live in the digestive tract are neither harmful nor beneficial. Different dietary items have different effects on these microorganisms. Some dietary items known as ‘prebiotics’ could increase the beneficial microorganism populations. Choosing such dietary items for regular consumption would contribute to improve the overall health of the individual.
A review of a large number of research studies carried out to find the effect of tea consumption on the microorganism populations in the digestive tract reveal that regular tea consumption assists in the reduction of harmful microorganism populations, whilst increasing the beneficial microorganism populations. The main beneficial impacts observed are reducing tooth decay and the risk of diseases with an inflammatory basis such as oral candidiasis, gastritis and peptic ulcers. In addition, high fluoride content in tea helps in the incorporation of fluoride into the teeth, making it more resistant toward tooth decaying bacteria.
The digestive system is a group of organs, working together to convert food through the digestion process into basic nutrients that could be absorbed into the body. The absorbed molecules will provide energy and building blocks to the entire body. Food passes through a long tube inside the body known as the alimentary canal or the gastrointestinal tract (GI tract). The GI tract is made up of the oral cavity, pharynx, oesophagus, stomach, small intestine and large intestine. Each part of the GI tract, assisted by other associated organs, play an important role in the digestion and absorption process.
The type of food consumed by an individual could have an influence, either harmful or beneficial, on the digestive tract. Choosing a diet which has beneficial effect on the digestive system will improve the overall health of the individual
Oral Cavity
Food begins its journey through the digestive system in the mouth, also known as the oral cavity. Inside the mouth are many accessory organs, such as tongue, teeth, and salivary glands, that aid the digestion of food. Teeth chop food into small pieces, which are moistened by saliva before the tongue and other muscles push the food into the pharynx or throat.
The action of teeth is to facilitate the digestion process. Without this action it would be difficult for the other parts of the digestive system to digest large particles of food. Tooth decay is a very common problem which could impair the digestion process, whilst being painful to the individual.
Fluoride and Tooth Decay
The tooth consists of a hard substance called calcium apatite, which forms the inner core called dentine and the outer layer called enamel, the hardest substance in the human body. Fluoride could react with calcium apatite in the teeth to form fluoroapatite, which has a more closely packed structure than apatite and more acid resistant. Fluoroapatite formation could occur during the formation of teeth and, also, when the developed tooth surface comes into contact with solutions such as tea which contain fluoride. Therefore, dietary fluoride will make the teeth more resistant to decay.
Tea is a major source of dietary fluoride and a typical cup of tea could contains 0.14 to 0.34 mg of fluoride. Therefore, regular tea consumption would provide significant amounts of fluoride that would strengthen teeth against decay.1
As the importance of fluoride has been recognised in relation to tooth decay, many countries and cities in the world have implemented fluoridisation of public water supply at the rates of 1-1.5 mg/l.2
Dental and Skeletal Fluorosis
Although fluoride is beneficial in reducing tooth decay, excessive fluoride intakes for long periods, in excess of 10 mg per day, could result in dental fluorosis and later in skeletal fluorosis.2 Dental fluorosis or mottled teeth will result in brownish patches on the teeth and is mainly an aesthetic issue. However, prolonged intake of excessive fluoride could later lead to skeletal fluorosis, due
to accumulation of fluoride in the bones. Skeletal fluorosis could cause pain and also damage to bone and joints.
The main cause for excessive fluoride intake is high fluoride content in the soil in certain regions. This will result in high fluoride levels in ground water and hence in drinking water. Further, agricultural products from these regions also would contain high fluoride, adding to dietary intakes.
Quality of Tea and Fluorosis
As tea contains significantly high fluoride compared to other dietary items, often tea is implicated with dental and skeletal fluorosis. However, it should be emphasised that consumption of good quality tea, with normal or fluoridated water, would not result in excessive intake of fluoride. The amount of fluoride in such a combination, good quality tea and normal or fluoridised water, would have beneficial effects against tooth decay.
However, as fluoride content increases with leaf maturity, fluoride content of inferior quality tea is higher than that of good quality tea. Typically, for the production of high quality tea, only the bud and the topmost two leaves are carefully hand plucked. This will indirectly ensure that mature leaf containing high fluoride would not come into the finished product. Some tea producing countries such as Sri Lanka, whose product is sold as ‘Ceylon Tea,’ practice hand plucking of tea to ensure the production of high quality tea. Certain other countries use mechanical
harvesting, where selective plucking of two leaves and a bud is not possible.
In fact, in certain countries where mechanical harvesting is practiced, sometimes mature branches are harvested and processed into made tea which would contain excessive amounts of fluoride. Therefore, it is important to choose tea produced in countries such as Sri Lanka to ensure ingestion of normal amounts of fluoride. Further, it is advisable to verify the sources of instant tea and ready to drink tea also, as they too could contribute to excessive intake of fluoride.
Dental Caries (Tooth Decay)
Tooth decay or cavity formation is due to the action of specific bacteria in the oral cavity. Bacteria are normally found in the GI tract including mouth. Harmful bacteria in the oral cavity could convert starch and sugar in the food pieces to acids. All these – bacteria, acid, food pieces, and saliva – combine in the mouth to form a sticky substance called plaque which adhere to the teeth. It is most common on the back molars, just above the gum line on all teeth, and at the edges of fillings. If plaque is not removed from the teeth by brushing, it turns into a substance called tartar, or calculus. Plaque and tartar irritate the gums, resulting in gingivitis (inflammation of the gums) and periodontitis (inflammation spreading into the ligaments and bone that support teeth).
Acid formed in plaque could damage the enamel (outermost layer on teeth) and form cavities. Cavities could further penetrate into the teeth and exposure of nerve tissues of the teeth cause
severe pain. However, regular consumption of fluoride containing food such as tea could strengthen the teeth and make them more acid resistant.
Effect of Tea on Tooth Decaying Bacteria
Streptococcus mutans is known as the main cariogenic (cavity forming) bacteria. Many research studies have been carried out to find the effect of tea on the populations of Streptococcus mutans. Recently a study done to assess the effect of mouth rinsing with green tea in comparison with chlorhexidine (a common mouthwash) and plain water, on Streptococcus mutans count in the oral cavity, revealed that green tea was equally effective as chlorhexidine.3
Many other similar studies had been done on the consumption of different types of tea including black, oolong and green tea. A review of these studies have concluded that the flavonoids in black, oolong and green tea have the ability to reduce the Streptococcus mutans populations and thus contribute to reduce the tooth decay.4
Further, many studies have revealed that regular tea consumption reduces the ability of these bacteria to get attached to teeth. These bacteria use an enzyme called glucosyltransferase to convert starch in the diet to sticky, water insoluble, glucans. These insoluble glucans help bacteria and other material in the oral cavity to adhere to the teeth and promote tooth decay. Therefore, glucosyltransferase inhibitors have the ability to reduce tooth decay. Tea has
been found to have the ability to inhibit the glucosyltransferase activity.5
Effect of Tea on Gingivitis and Periodontal Disease
Dental plaque formation could irritate the gums, resulting in Gingivitis or the inflammation of the gums. Gingivitis could lead to periodontitis where inflammation spreads into the ligaments and bone that support teeth. The amount of research studies carried out on the effect of tea on gingivitis and periodontal diseases are relatively less. In vitro (outside a living organism) studies have demonstrated the ability of tea flavonoids to inhibit bacteria such as Porphyromonas gingivalis which contribute to gingivitis and periodontal disease.6 Limited number of in vivo (inside a living organism) studies also indicate an inhibitory effect of tea on gingivitis and periodontal disease.7 However, further clinical trials are required to confirm the inhibitory effect of tea on gingivitis and periodontal disease.
Effect of Tea Consumption on Inflammation of the Oral Cavity
Inflammation of the oral cavity is a common disease which affects the mucous membranes in the oral cavity. Diverse factors contribute to the origin of a range of oral inflammatory diseases. One common form of oral inflammation is caused by the presence of the fungus called Candida. Many species of Candida could live in moist cavities of the human body. A limited number of research studies indicate that tea could inhibit the growth of many species of Candida.8
Effect of Tea Consumption on the Micro-Organisms in the Digestive Tract
Micro-organisms live throughout the digestive tract, from the oral cavity up to the anus. Some of these micro-organisms are beneficial whilst others are harmful. Yet other micro-organisms in the human GI tract, neither harmful nor beneficial, called “commensal micro-organisms,” derive a benefit from the host whilst remaining neutral in impact.
Different dietary items have an effect on this large array of micro-organisms that live in the GI tract. Some of the dietary items could reduce the harmful micro-organisms whilst others may reduce the beneficial micro-organisms. Therefore, it is possible to improve one’s health by choosing, for regular consumption, the dietary items which increase beneficial micro-organisms and reduce the harmful micro-organisms. Such dietary items that encourage the growth of beneficial micro-organisms in the GI tract are known as ‘prebiotics’. Certain food items such as fermented milk products could introduce beneficial microorganisms to the GI tract. Such food items are known as ‘probiotics’.
Research focused on ascertaining the effect of tea consumption on the micro-organisms that live in the GI tract has revealed that regular tea consumption results in the suppression of harmful micro-organisms while increasing the beneficial organisms. A team of scientists from the National University of Singapore found that different strains of intestinal bacteria had varying
degrees of growth sensitivity to tea phenolics and metabolites. The growth of certain pathogenic bacteria, such as Clostridium perfringens, Clostridium difficile and Bacteroides spp. was significantly repressed by tea polyphenols and their derivatives, while commensal bacteria like Clostridium spp., Bifidobacterium spp. and probiotics such as Lactobacillus spp. were less severely affected. This indicates that tea polyphenols exert significant effects on the intestinal environment, through modulation of the intestinal bacterial population, probably by acting as metabolic prebiotics.9
Helicobacter pylori is a harmful bacteria that causes infection in the stomach. It lives in approximately two-thirds of the world population. It is one of the main factors that lead to gastritis, which is caused by the inflammation of the lining of the stomach. Prolonged presence of Helicobacter pylori in the GI tract could lead to peptic ulcer, a sore in the lining of the stomach or duodenum, the first part of small intestine. A pain with a burning sensation in the stomach is the most common symptom of peptic ulcers. Formation of peptic ulcers by Helicobacter pylori increases the risk of developing stomach cancer.
Studies focused on examining the effect of tea consumption on the growth of Helicobacter pylori have revealed that both black and green tea consumption reduces Helicobacter pylori infection, indicating that regular tea consumption could contribute to the reduction of the risk of gastritis, peptic ulcers and stomach cancer.10
Effect of Tea Consumption on Oesophageal Cancer
Incidence of oesophageal cancer is more prevalent in Asian countries. An “oesophageal cancer belt” has been identified, which extends from northeast China to the Middle East through the Himalayan region. Tea consumption in these region is very high compared to the other parts of the world, and could be as high as twenty five cups per day. Therefore, when research began on the oesophageal cancer in this region tea consumption was suspected as the prime culprit. However, detailed research later had proven that tea consumption is not a risk factor, but that it contributed to a lowering of the risk.11 People in this region have the habit of consuming very hot beverages and food, probably to alleviate the cold. Later it had been confirmed that the real culprit was the consumption of very hot food and beverages including very hot tea.12
Temperatures in the range of 130 to 160 °F (~ 55 to 71 0C) , are recommended for hot beverages considering the safety of consumers. Those temperatures are significantly below temperatures that are used during brewing processes, which is generally 200 0F (93 0C) for tea and when poured into the cup for serving, it would be around 191 to 196 0F (91 to 90 0C).13
Recent Research on Tea Consumption and Oral and Digestive Tract Health
In the past, research on tea consumption and oral health mostly focused on tooth decay and microorganisms that cause inflammation in the oral
cavity. Recently, attention was focussed on other areas too.
Periodontitis, also called gum disease, is a serious gum infection that damages the soft tissue of the gum and, without treatment, can destroy the bone that supports teeth. Periodontitis can cause teeth to become loose or lead to tooth loss. It is a major cause of tooth loss globally. Recently, data from the National Health and Nutrition Examination Survey (NHANES), a cross-sectional study in the US, carried out from 2009 to 2014
with 10,010 individuals, was analysed to find the relationship between dietary patterns and the periodontitis. Conclusions of the study were, most dietary patterns identified were not associated with periodontitis extent. One pattern, however, rich in salad, fruit, and vegetables and with plain water or tea to drink, was associated with lower periodontitis and loss of teeth.14
Halitosis is an oral health problem where the major symptom is bad smelling breath. It could be caused by several factors including the presence of certain types of odour causing bacteria. A recent systematic review has scrutinised data from all available clinical trials on tea consumption and halitosis. Conclusion of the study was that tea can reduce halitosis through anti-microbial effects.15
Attention had also been focused on the use of tea-based mouth washes. A systematic review of research on tea-based mouth washes, in comparison with Chlorhexidine (most widelyused chemical in mouth washes) mouth washes, concluded that tea-based mouthwashes can be considered an alternative to chlorhexidine mouthwashes in sustaining oral hygiene.16
Results of these studies indicate that regular tea consumption will result in the reduction of pathogenic micro-organism populations in the oral cavity, which cause all types of oral diseases.
Recently, attention has been focused on the effect of tea consumption on Crohn’s disease and Ulcerative colitis, inflammatory bowel disease. Crohn’s disease, is a type of inflammatory bowel disease, which causes inflammation of digestive
tract, which can lead to abdominal pain, severe diarrhoea, fatigue, weight loss and malnutrition. Ulcerative colitis, another inflammatory bowel disease, causes irritation, inflammation, and ulcers in the lining of the large intestine. Systematic reviews on the research carried out so far on these diseases, concluded that tea consumption could reduce the risk of these two diseases.17
Results from all these recent studies, further confirm that regular tea consumption leads to a reduction of harmful micro-organisms in the digestive tract from the oral cavity to the colon and, thereby, reducing the risk of many diseases caused by these micro-organisms.
Conclusions
A large number of micro-organisms, some beneficial and others harmful, live in the digestive tract of humans. Another set of micro-organisms known as ‘commensal micro-organisms’ have neither beneficial nor harmful effects on humans. Regular dietary items have an effect on the populations of these micro-organisms. A review of the results from the studies on tea consumption and micro-organisms of the digestive tract, indicates that it generally results in the reduction of harmful micro-organism populations, while increasing the beneficial micro-organism populations. Main effects of this activity are reduction of tooth decay and the diminution of the risk of diseases with an inflammatory basis, such as oral candidiasis, gastritis and peptic ulcers.
ɇ Regular tea consumption reduces the risk of tooth decay, by reducing the populations of tooth decaying bacteria and also by reducing their ability to adhere to the teeth. In addition, fluoride in tea contributes to strengthen teeth and making them more resistant towards decay.
ɇ Although fluoride helps in strengthening teeth, excessive fluoride consumption for a long period of time could lead to dental fluorosis (mottled teeth) and later skeletal fluorosis, causing pain and also damage to bone and joints.
ɇ Consumption of good quality tea with normal or fluoridated water would not result in excessive intake of fluoride. However, fluoride content of inferior quality teas are higher than that of good quality tea, as mature leaves are used for the production of inferior quality tea. Therefore, tea should be selected from a source such as Sri Lanka, where only the tender shoots are carefully hand plucked for processing into a high quality end product.
ɇ Regular tea consumption results in the reduction of harmful micro-organism populations throughout the digestive tract, while increasing the beneficial microorganism populations. Main effects observed due to this are reducing tooth decay and the risk of diseases with an inflammatory basis, such as oral candidiasis, gastritis and peptic ulcers.
REFERENCES
1. Puneet Goenka, Aditi Sarawgi, Vinayak Karun, Anant G. Nigam, Samir Dutta and Nikhil Marwah, 2013, Camellia sinensis (Tea): Implications and role in preventing dental decay, Pharmacognosy review, 7(14), 152–156.
2. Fluoride in drinking water, 2006, World Health organization, Available at www.who.int/publications/i/item/9241563192, accessed on 21st August 2022.
3. Neturi RS, Srinivas R, Vicram Singha B, Sandhya Sree Y, Chandra Shekar T, Siva Kumar P, 2014, Effects of Green Tea on Streptococcus mutans Counts- A Randomised Control Trial, Journal of Clinical and Diagnostic Research, 8(11), ZC128-130.
4. Ferrazzano GF, Amato I, Ingenito A, De Natale A, Pollio A, 2009, Anti-cariogenic effects of polyphenols from plant stimulant beverages (cocoa, coffee, tea), Fitoterapia, 80(5), 255-262.
5. Hamilton-Miller JM, 2001, Anti-cariogenic properties of tea (Camellia sinensis), Journal of Medical Microbiology, 50(4), 299-302
6. Sakanaka S, Aizawa M, Kim M, Yamamoto T, 1996, Inhibitory effects of green tea polyphenols on growth and cellular adherence of an oral bacterium, Porphyromonas gingivalis, Bioscience Biotechnology and Biochemistry, 60(5), 745-749
7. Neeraj Deshpande, Anshula Deshpande, Salma Mafoud, 2012, Evaluation of intake of green tea on gingival and periodontal status: An experimental study, Journal of Interdisciplinary Dentistry, 2(2), 108-112.
8. Sitheeque MA, Panagoda GJ, Yau J, Amarakoon AMT, Udagama UR, Samaranayake LP, 2009, Antifungal activity of black tea polyphenols (catechins and theaflavins) against Candida species, Chemotherapy, 55(3), 189-196.
9. Lee HC, Jenner AM, Low CS, Lee YK, 2006, Effect of tea phenolics and their aromatic fecal bacterial metabolites on intestinal microbiota, Research in Microbiology, 157(9), 876-884.
10. Boyanova L, Ilieva J, Gergova G, Vladimirov B, Nikolov R, Mitov I, 2015, Honey and green/black tea consumption may reduce the risk of Helicobacter pylori infection, Diagnostic Microbiology and Infectious Diseases, 82(1), 85-86.
11. Zheng JS, Yang J, Fu YQ, Huang T, Huang YJ, Li D, 2013, Effects of green tea, black tea, and coffee consumption on the risk of esophageal cancer: a systematic review and meta-analysis of observational studies, Nutrition and Cancer, 65(1), 1-16.
12. Jing Lin, Runming Zeng, Weihua Cao, Rongcheng Luo, Jing Chen, Yuan Lin, 2011, Hot Beverage and Food Intake and Esophageal Cancer in Southern China, Asian Pacific Journal of Cancer Prevention, 12, 2189-2192.
13. John Abraham and Kenneth Diller, 2019, A Review of Hot Beverage Temperatures - Satisfying Consumer Preference and Safety, Journal of Food Science, 84 (8), 2011-2014
14. David M Wright et al, Association between diet and periodontitis: a cross-sectional study of 10,000 NHANES participants, The American Journal of Clinical Nutrition, doi.org/10.1093/ajcn/nqaa266
15. Bahareh Tahani and Roya Sabzian, Effect of Camellia sinensis plant on decreasing the level of halitosis: A systematic review, Dental Research Journal, Nov-Dec 2018;15(6):379-384
16. Ankita Mathur et al, Efficacy of green tea-based mouthwashes on dental plaque and gingival inflammation: A systematic review and meta-analysis, Indian Journal of Dental Research, Mar-Apr 2018;29(2):225-232, doi: 10.4103/ijdr.IJDR_493_17
17. Daniele Piovani et al, Environmental Risk Factors for Inflammatory Bowel Diseases: An Umbrella Review of Meta-analyses, Gastroenterology, 2019 Sep;157(3):647-659.e4, doi: 10.1053/j.gastro.2019.04.016
Effect of Tea Consumption on the Brain Function and Mood
Caffeine and theanine in tea are the constituents that have an effect on the Central Nervous System (CNS). Caffeine is a well-known stimulant that could make you alert and relieve fatigue. Theanine also impacts on the CNS and its main effect is relaxation of mood. Caffeine is known to stimulate a person and improve performance and performance speed. Recent research has found that theanine also has similar effects and, together, theanine and caffeine have synergistic impact. Therefore, tea, the only beverage in which both caffeine and theanine are present together, could improve performance, whilst inducing a relaxed mindset. Therefore, tea is an ideal beverage to refresh a person and prepare him for work. Polyphenols and caffeine in tea may have protective effects against dementia and Alzheimer’s disease as they could play a role in reducing neuro-degradation and amyloid plaque formation in the brain.
Tea contains two main constituents, caffeine and theanine, which have an effect on the CNS (comprises the brain and spinal cord that controls the activities of the body.)
Caffeine
Caffeine Content in Tea, Absorption and Metabolism
A typical high quality cup of tea contains approximately 40-50 mg of caffeine, although the range could vary between 20 to 90 mg. After ingestion caffeine is rapidly absorbed from the digestive tract into the blood stream, with more than 90% of caffeine being absorbed within 45 minutes of ingestion. Peak blood concentrations are observed between 15 and 120 minutes. The wide variation of time taken to achieve peak blood concentrations in individuals, is due to the interference of other dietary components which have an effect on caffeine absorption. Caffeine readily passes through all the membranes in the body and therefore is distributed throughout the body. It could also readily pass through the ‘blood brain barrier’ (Only certain compounds in the blood are allowed to enter the brain; this is known as ‘blood-brain barrier’) and therefore reaches the brain after ingestion.
Caffeine entering the body is metabolised by the liver and then excreted through the kidney. The half-life of caffeine in the body could vary between 2.5 to 7.5 hours (half -life is the period of time required for the concentration in the body to be reduced by half; half-life depends on how quickly the compound is eliminated from the body). Considerable variation in the half-life for caffeine is due to the individual differences
in the clearance of caffeine, mainly attributable to genetic variations between individuals. In addition, smoking, oral contraceptive use, hormone replacement therapy and liver diseases could have an effect on caffeine clearance.1
Physiological Effects of Caffeine
After ingestion caffeine reaches the brain quickly and could have stimulating effects, the most noticeable being heightened alertness. It can also re-energise. Therefore, a cup of tea could refresh a fatigued individual. Primary mechanisms for stimulatory activity are the blocking of adenosine receptors and the inhibition of phosphodiesterases.2
In addition to stimulating effect, caffeine could increase the blood pressure slightly for a short duration after ingestion. However, in most people, there is no long-term effect on blood pressure. Caffeine could have an effect on heart rate also. Therefore, individuals with an irregular heart rhythm should consult a medical practitioner about the use of caffeinated beverages.3
Safety of Caffeine
As it could have an impact on blood pressure and heart rate, there are concerns about the caffeine intake, although the effects are only short term. There have been many scientific reviews on caffeine safety and maximum levels that should be ingested per day. The latest comprehensive review has been carried out by the European Food Safety Authority (EFSA) in 2015. The panel of experts have extensively reviewed the scientific data available and have given a ‘scientific opinion on the safety of caffeine’ in a detailed report.4
According to the report, single doses of caffeine up to 200 mg (about 3 mg/kg body weight for a 70-kg adult) do not result in any negative effects. Further, habitual caffeine consumption up to 400 mg per day (about 5.7 mg/kg bw per day for a 70kg adult) also does not give rise to any negative effects in adults.
Caffeine could pass through the placenta of a pregnant mother to the foetus. Therefore, there are concerns about using caffeinated beverages during pregnancy. The EFSA report had found that only very high doses of caffeine, which could not be achieved by consuming tea, could have an effect on the foetus. However, as a precaution, they have recommended restricting daily caffeine intake to 200 mg per day during pregnancy. Further, as caffeine could pass from lactating mothers to the baby, the EFSA report advises to restrict caffeine intake for lactating mothers to 200 mg per day, which would be present in approximately four cups of tea.
EFSA report had recommended the maximum intake of caffeine in a single dose for adults as the limit for habitual (or daily) consumption for children, which is 3 mg/kg of body weight. Therefore, the weight of the child has to be taken into account when calculating the maximum intake of caffeine per day for children. For example, a child with 50 kg body weight could consume a maximum of 150 mg of caffeine per day (3 mg/kg body weight x 50 kg).
Accordingly, healthy adults could easily consume six cups of tea, which would theoretically contribute a maximum of 300 mg of caffeine per day.
Effect of Caffeine on Sleep, Anxiety and Behavioural Changes
In adults, single doses of caffeine of about 100 mg (1.4 mg/kg of body weight per day in a 70-kg adult) have been shown to increase sleep latency and reduce sleep duration, when consumed close to bedtime. However, doses < 100 mg do not appear to have such an effect on sleep. Therefore, a cup of tea before bedtime would not affect the sleep of a healthy adult.
Higher doses of caffeine (≥ 400–500 mg), consumed either on a single occasion or within short periods of time, have been reported to increase anxiety upon oral consumption, mostly in patients with psychiatric anxiety disorders, but occasionally in healthy adults, particularly if they are non-habitual caffeine consumers. Therefore, typical amounts of caffeine in tea would not lead to anxiety in healthy adults.
According to the EFSA report, regular consumption of caffeine up to about 3 mg/kg body weight per day does not appear to induce behavioural changes in children, adolescents and adults.
Experimental evidence suggests that typical amounts of caffeine consumed with a cup of tea would not affect sleep, anxiety or behaviour of healthy individuals. However, some individuals have strong perceptions about the effect of caffeine. These perceptions, rather than actual effects of caffeine, sometimes could have an effect on the individual’s sleep or anxiety.
Theanine
Theanine is a unique, non-protein forming amino acid. The tea plant is the only agricultural crop that contains theanine. Therefore, theanine is not present in any other plant based food or beverage except tea. Tea leaf contains 1-2% of theanine on a dry weight basis.
Theanine gives the umami taste (unique brothy or savoury taste). Although not very important in black tea, theanine makes a noteworthy contribution to the taste of green tea.
Theanine attracted the attention of scientists when it was found that theanine ingestion resulted in alterations in neural oscillations. Neural oscillation is rhythmic or repetitive neural activity in the central nervous system. Synchronised activity of large numbers of neurons can give rise to macroscopic oscillations, which can be observed in an electroencephalogram (recording of the electrical activity of the brain). Macroscopic oscillations are commonly referred to as ‘brain waves’. The type of brain waves emitted gives an indication of the activity and status of the brain. Scientific experiments have demonstrated that theanine ingestion increases the alpha wave production in the brain,5 which point to a relaxed brain state. Further, alpha waves indicate that the alertness is not reduced and that the individual is not drowsy or sleepy.
In addition, research had shown that theanine has a neuro-protective effect and also acts as a cognitive enhancing agent.6 (Cognition is the
mental action or process of acquiring knowledge and understanding through thought, experience, and the senses.)
Several research studies, focused on the effect of theanine in tea on mood, attention and performance of individuals, have been reviewed in the American Journal of Clinical Nutrition.7
According to the review, theanine in tea has an effect on the attention of an individual and, therefore, results in better performance when a particular task is given. Further, theanine in tea was found to reduce anxiety by inducing relaxation. Owing to these effects theanine in tea was found to improve creative problem solving. Therefore, overall, theanine in tea would both relax, restore and improve individual performance.
Caffeine is known to improve the reaction time after ingestion. A recent study has found that theanine could also improve the reaction time of an individual.8
Theanine and Memory
Research studies on animal models have found that theanine could improve memory. 9, 10 However, evidence from human clinical trials is not adequate yet to make a firm conclusion.
Caffeine and Theanine Combination on Brain Functions
Caffeine and theanine combination is naturally found only in tea. As both could have impacts on the brain, many research studies have focused attention on the effects of these two compounds
together. Caffeine is known to make an individual alert and improve performance speed. On the other hand, theanine makes one relaxed but not drowsy or sleepy. Recent studies also have found that theanine could improve the attention and performance of an individual, whilst the two, in combination, produces a synergistic and additive impact on performance. Therefore, the overall impact of caffeine and theanine together could be summarised as inducing performance speed and accuracy, whilst maintaining emotional equilibrium.7
Recently, research studies on the effect of combination of caffeine and theanine on the function of brain have been systematically reviewed, indicating that a combination of caffeine and theanine has favourable clinical significance in the domains of attention, memory and cognition in the brain. Overall, the authors conclude that the combination of l-theanine and caffeine is a safe and effective cognitive enhancer. 11
Dementia and Alzheimer’s Disease
Dementia is the loss of cognitive function (thinking, remembering, reasoning and behavioural abilities). Severity of dementia could range from the mildest stage, when it is just beginning to affect a person’s functioning, to the most severe stage, when the person must depend completely on others for basic activities of daily living.
Alzheimer’s is the most common form of dementia among older adults. Alzheimer’s disease
is ranked as the sixth leading cause of death in the United States. Recent estimates indicate that it may rank third, just behind heart disease and cancer as a cause of death among older people in US.12
Gradual changes in the brain during the development of Alzheimer’s disease are the abnormal deposits of proteins, forming ‘amyloid plaques’ and ‘neurofibrillary tangles’ throughout the brain. The healthy neurons (nerve cells) stop functioning, lose connections with other neurons, and die. Scientists have not fully understood what causes Alzheimer’s disease. It arises from a complex series of brain changes that occur over decades. The causes probably include a combination of genetic, environmental, and lifestyle factors. Among the lifestyle factors, regular exercise and higher intake of polyphenols and caffeine are known to reduce the risk of the Alzheimer’s disease.
Effect of Tea Consumption on Dementia and Alzheimer’s Disease
Neuro-inflammation and oxidative stress have been considered major causes in dementia and Alzheimer’s disease, playing a crucial role in neurotoxicity and the destruction of nerve cells. Therefore, antioxidants may reduce the development and improve the treatment of neurodegenerative diseases and dementia. Several studies have demonstrated the neuroprotective abilities of plant polyphenolic compounds. Review of such research on plant polyphenols, including tea polyphenols, indicate that they have a protective effect on neurodegradative diseases.13
It has been demonstrated that both green tea polyphenols (EGCG) and black tea polyphenols (theaflavin) have the ability to inhibit the formation of ‘amyloid plaques’ and ‘neurofibrillary tangles’.14, 15
Further, review of the data form scientific studies reveal that caffeine also reduces the risk of developing Alzheimer’s disease.16
Above research indicates that regular tea consumption may reduce the risk of development of neuro-degenerative diseases, including Alzheimer’s disease.
Review of the population studies reveal that tea drinking is inversely associated with the risk of cognitive impairment. Although some of the relatively short-term studies reveal that tea consumption has a protective role against Alzheimer’s disease, systematic review of the data suggests that a definitive conclusion cannot be made yet on an inverse relationship between tea consumption and Alzheimer’s disease. Larger studies with longer follow-up periods are required to make definitive conclusions.17, 18
Research has also demonstrated that polyphenols and caffeine in tea may have protective effects against dementia and Alzheimer’s disease, as they could play a role in reducing neuro-degradation and amyloid plaque formation in the brain.
Effect of Tea on Stress, Anxiety and Sleep Quality
In addition to the brain function and mood, recently, research has focused on the effect of tea on stress and anxiety also. Stress relieving action
of tea, especially due to the presence of theanine, has been demonstrated in several human clinical trials.
In one such experiment carried out in Japan, the effect of consumption of Matcha green tea on stress and anxiety were studied. As anxiety is a reaction to stress, to assess the anxiety of participants, a test called the state-trait anxiety inventory (STAI) test was carried out. In addition, to assess the physiological stress response, a marker for stress, salivary amylase activity (sAA) was measured. Conclusion of the study was that Matcha green tea has a stress-reducing effect.19
In another similar study, effect of low caffeine green tea on stress and sleep quality has been studied. Physiological stress was monitored by measuring salivary amylase activity (sAA), and sleep hours and quality were monitored through a questionnaire, combined with an overnight EEG (Electroencephalogram, to monitor the quality of sleep). Conclusions of the study were that ingestion of green tea lowered the stress and significantly improved sleep quality and reduced fatigue in the morning.20
Furthermore, the effect of a theanine-based nutritional drink has been assessed for the effects on stress, fatigue and mood in a study done in Australia. Stress status of the participants were assessed by measuring salivary cortisol, employing a multi-task activity and through MEG (Magnetoencephalography, a neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain). The findings of
the study is that theanine possesses anti-stress effects.21
A number of randomised controlled trials have been carried out to find the effect of theanine on stress responses and anxiety levels in humans under stressful conditions. Results from nine such clinical trials were systematically reviewed recently. The outcome of the review was that theanine may assist in the reduction of stress and anxiety in people exposed to stressful conditions.
22
A recent review of research studies carried out so far on the effect of tea components on sleep quality has concluded that theanine in tea improves sleep quality. In addition, they concluded that fatigue after awakening was also reduced due to tea.23
Based on the findings of the above studies it could be concluded, that tea consumption may reduce stress and anxiety through the action of theanine and also improve sleep quality.
Conclusion
Main effects of caffeine are the improvement of alertness and relief from fatigue, while theanine generates a relaxing effect. The unique combination of caffeine and theanine is found only in tea. Recent research has found that both caffeine and theanine synergistically improve attention and performance. Therefore, a cup of tea could make one alert and also relaxed while improving performance. Hence, tea would be an ideal beverage to consume in the workplace to refresh you and continue working.
Polyphenols and caffeine in tea may have protective effects against dementia and Alzheimer’s disease, as they could play a role in reducing neuro-degradation and amyloid plaque formation in the brain.
Recent research has found that theanine in tea could reduce anxiety stress and also improve sleep quality.
ɇ Caffeine could make an individual alert and provide relief from fatigue.
ɇ Theanine could induce relaxation.
ɇ Bothe caffeine and theanine, a combination found only in tea, could improve the performance of an individual whilst inducing relaxation. Therefore, tea is an ideal beverage for consumption in the workplace.
ɇ Polyphenols and caffeine in tea may have protective effects against dementia and Alzheimer’s disease.
ɇ Theanine in tea could reduce anxiety and stress and also improve sleep quality.
REFERENCES
1. Pharmacology of Caffeine, In: Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations, Institute of Medicine (US) Committee on Military Nutrition Research, Washington (DC): National Academies Press (US); 2001.
2. Ribeiro JA, Sebastiao AM, 2010, Caffeine and adenosine, Journal of Alzheimer’s Disease, 20 Suppl 1:S3-S15
3. Riksen NP, Smits P, Rongen GA, 2011, The cardiovascular effects of methylxanthines, Hand book of Experimental Pharmacology, 200, 413-437
4. European Food Safety Authority, 2015, Scientific opinion on the safety of caffeine, EFSA Journal, 13(5), 4102, Available at www.efsa. europa.eu/en/efsajournal/pub/4102 Accessed on 22nd August 2022
5. Manuel Gomez-Ramirez, Beth A. Higgins, Jane A. Rycroft, Gail N. Owen, Jeannette Mahoney, Marina Shpaner and John J. Foxe, 2007, The Deployment of Intersensory Selective Attention: A High-density Electrical Mapping Study of the Effects of Theanine, Clinical Neuropharmacology, 30, 25-38
6. Nathan PJ, Lu K, Gray M, Oliver C, 2006, The neuropharmacology of L-theanine (N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent, Journal of Herbal Pharmacotherapy, 6(2), 21-30.
7. Suzanne J Einother and Vanessa E Martens, 2013, Acute effects of tea consumption on attention and mood, American Journal of Clinical Nutrition, 98, 1700S–1708S.
8. Kahathuduwa CN, Dassanayake TL, Amarakoon AMT, Weerasinghe VS, 2016, Acute effects of theanine, caffeine and theanine-caffeine combination on attention, Nutritional Neuroscience. 2016 Feb, DOI: 10.1080/1028415X.2016.1144845
9. Tamano H, Fukura K, Suzuki M, Sakamoto K, Yokogoshi H, Takeda A, 2013, Preventive effect of theanine intake on stress-induced impairments of hippocamapal long-term potentiation and recognition memory, Brain Research Bulletin, 95, 1-6
10. Takeda A, Sakamoto K, Tamano H, Fukura K, Inui N, Suh SW, Won SJ, Yokogoshi H, 2011, Facilitated neurogenesis in the developing hippocampus after intake of theanine, an amino acid in tea leaves, and object recognition memory, Cellular and Molecular Neurobiology, 31(7), 1079-1088.
11. Anas Anas Sohail et al, The Cognitive-Enhancing Outcomes of Caffeine and L-theanine: A Systematic Review, The Cureus Journal of Medical Science, 2021 Dec, doi: 10.7759/cureus.20828
12. Alzheimer’s disease fact sheet, National Institute on Aging, US Department of Health and Human Services. Available at, www.nia.nih. gov/alzheimers/publication/alzheimers-disease-fact-sheet accessed on 22nd August 2022.
13. Spagnuolo C, Napolitano M, Tedesco I, Moccia S, Milito A and Russo GL, 2016, Neuroprotective Role of Natural Polyphenols, Current Topics in Medicinal Chemistry, 16(17), 1943-1950.
14. Grelle G, Otto A, Lorenz M, Frank RF, Wanker EE and Bieschke J., 2011, Black tea theaflavins inhibit formation of toxic amyloid-β and α-synuclein fibrils, Biochemistry, 50(49), 10624-10636.
15. Rezai-Zadeh K, Arendash GW, Hou H, Fernandez F, Jensen M, Runfeldt M, Shytle RD and Tan J., 2008, Green tea epigallocatechin-3gallate (EGCG) reduces beta-amyloid mediated cognitive impairment and modulates tau pathology in Alzheimer transgenic mice, Brain Research, 12(1214), 177-187.
16. Nehlig A, 2016, Effects of coffee/caffeine on brain health and disease: What should I tell my patients?, Practical Neurology, 16(2), 89-95.
17. Ma QP, Huang C, Cui QY, Yang DJ, Sun K, Chen X and Li XH, 2016, Meta-Analysis of the Association between Tea Intake and the Risk of Cognitive Disorders, PLOS One, DOI: 10.1371/journal.pone.0165861.
18. Panza F, Solfrizzi V, Barulli MR, Bonfiglio C, Guerra V, Osella A, Seripa D, Sabbà C, Pilotto A and Logroscino G, 2015, Coffee, tea, and caffeine consumption and prevention of late-life cognitive decline and dementia: a systematic review, Journal of Nutrition Health and Aging, 19(3), 313-328.
19. Keiko Unno et al, Stress-Reducing Function of Matcha Green Tea in Animal Experiments and Clinical Trials, Nutrients, 2018 Oct 10;10(10):1468, doi: 10.3390/nu10101468
20. Keiko Unno et al, Reduced Stress and Improved Sleep Quality Caused by Green Tea Are Associated with a Reduced Caffeine Content, Nutrients, 2017 Jul 19;9(7):777, doi: 10.3390/nu9070777
21. David J White et al, Anti-Stress, Behavioural and Magnetoencephalography Effects of an L-Theanine-Based Nutrient Drink: A Randomised, Double-Blind, Placebo-Controlled, Crossover Trial, Nutrients, 2016 Jan 19;8(1):53, doi: 10.3390/nu8010053
22. Jackson L. Williams et al, The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review, Plant Foods for Human Nutrition, 2020 Mar;75(1):12-23, doi:10.1007/s11130-019-00771-5
23. Yang Wei et al, Recent advances in the utilisation of tea active ingredients to regulate sleep through neuroendocrine pathway, immune system and intestinal microbiota Critical Reviews in Food Science and Nutrition, 2022 March, doi.org/10.1080/10408398.2022.2048291
Effect of Tea Consumption on Weight Loss and Obesity
Worldwide, obesity has more than doubled since 1980 and has become an important global health issue. Excess weight and obesity are major risk factors for a number of chronic diseases, including diabetes, cardiovascular diseases and cancer. Therefore, any strategy for weight reduction would be very important. Research has demonstrated that tea consumption could contribute to weight loss and weight maintenance. A cup of tea, without milk or sugar, contains almost zero calories. Therefore, consumption of a cup of plain tea between main meals, instead of any other snacks, would significantly contribute to weight maintenance. Further, research has shown that tea consumption could contribute to weight reduction through many other mechanisms. These include reduced fat absorption from the diet, alterations in fat metabolism resulting in lower storage of fat and increased energy expenditure resulting in increased use of fat. Many human clinical studies and population studies, involving large numbers of individuals, also have confirmed that tea consumption contributes to reduced obesity and weight maintenance. Regular tea consumption for longer periods has more pronounced effects on weight reduction
Excess weight and obesity are defined as abnormal or excessive fat accumulation that presents a risk to health. Obesity is measured using the body mass index (BMI), a person’s weight (in kilogrammes) divided by the square of his or her height (in metres). A person with a BMI of 30 or more is generally considered obese. A person with a BMI equal to or more than 25 is considered overweight.
Excess weight and obesity are major risk factors for a number of chronic diseases, including diabetes, cardiovascular diseases and cancer. Worldwide, obesity has more than tripled since 1975. In 2016, more than 1.9 billion adults were overweight and over 650 million of them were obese. Total overweight population was 39% of the adult population and 13% of the total population were obese. Once considered a problem only in high income countries, excess weight and obesity are now dramatically on the rise in low and middle income countries, particularly in urban areas.
Obesity among children is also increasing at an alarming rate. According to WHO in 2016, over 340 million children and adolescents aged 5 -19 were overweight or obese globally. 39 million children under the age of 5 were overweight or obese in 2020. The rate of increase is 30% higher in low and middle income countries, than that of developed countries. If current trends continue 70 million young children will be overweight or obese by 2025.
The fundamental cause of obesity and excess weight is an energy imbalance between calories
consumed and calories used. Globally, there has been an increased intake of energy-dense food that are high in fat, accompanied by a drift towards physical inactivity, due to the increasingly sedentary nature of many forms of work, changing modes of transportation and increasing urbanisation. These have contributed to obesity.
Raised BMI is a major risk factor for NonCommunicable Diseases (NCDs) such as cardiovascular diseases (mainly heart disease and stroke), diabetes, cancer and musculo-skeletal disorders such as osteoarthritis, which is a highly-disabling degenerative disease of the joints.
The risk for these NCDs increases, with increases in BMI.
Childhood obesity is associated with a higher propensity to obesity, premature death and disability in adulthood. But, in addition to increased future risks, obese children experience breathing difficulties, increased risk of fractures, hypertension, early signs of cardiovascular disease, insulin resistance and psychological effects.1, 2
The role of tea consumption on obesity and weight loss has been extensively studied since 1900s. Polyphenols and caffeine in tea have been identified as being responsible for the prevention of obesity, and the interaction between these compounds has also been studied.
Mechanisms of Weight Reduction by Components of Tea
A cup of tea, without milk or sugar, contains almost zero calories (see chapter 2 for details). Therefore, when a person yearns for a snack between main meals, if a cup of plain tea is consumed, it would significantly contribute to weight maintenance. The habit of consuming tea, instead of snacks, could be developed over time by choosing a high quality tea according to taste preferences.
Research has shown that tea consumption could contribute to weight reduction through several mechanisms in the human body.
Absorption of Nutrients from the Digestive Tract
Fat in the diet is present as triglycerides, which cannot be absorbed directly from the digestive tract. Triglycerides are first digested, or broken down, to fatty acids by an enzyme called lipase, secreted by the pancreas. Fatty acids are then absorbed from the digestive tract and circulated through the blood stream. Several research studies have shown that tea polyphenols could inhibit the pancreatic lipase enzyme and reduce the fatty acid absorption.3, 4
Microorganisms in the Digestive Tract and Fat Absorption
Large populations of microorganisms that live in the digestive tract also help in the digestion and absorption of fat and other nutrients. Research studies have shown that tea consumption could alter the populations of these microorganisms.
Tea polyphenols could reduce microorganisms which contribute to digestion and absorption of fat, thus inhibiting the absorption of fat from the digestive tract. 5, 6
Effect of Tea on Fat Metabolism in the Human Body
A complicated signalling system and enzymes control the synthesis of fat, usage of fat, and storage of fat in the human body. Research studies have shown that tea polyphenols could interfere with this signalling mechanism, resulting in a reduction of synthesis and storage of fat while improving fat breakdown. These research studies have demonstrated that this mechanism, induced by tea polyphenols, significantly contributes to weight reduction in humans.6, 7
Effect of Tea on Energy Expenditure
The stimulating effect of tea is due to caffeine which acts on the human Central Nervous System (CNS). Research has found that in addition to the stimulation effect, caffeine could also increase the energy expenditure in the body. Tea polyphenols also contribute to increased energy expenditure by synergistically acting with caffeine. This will result in increased use of energy, or burning more calories after a cup of tea, which contributes to weight reduction. However, research studies carried out so far indicate that the contribution of this mechanism to weight reduction is relatively low, compared to the above two mechanisms.8
Population Studies
Many human clinical studies have been conducted to examine the effect of tea consumption on obesity. These studies have shown that tea consumption contributes to weight reduction and reduces the risk of obesity.
Early studies have established that tea and polyphenolic extracts from tea have the ability to reduce body weight and body fat.
In 2005, a study had been carried out in Tokyo, using 38 healthy males, aged 24–46 years, whose body weights ranged from normal to overweight. They were given a tea extract containing 690 mg of catechins per day for 12 weeks and compared with a control group consuming a low catechin extract (22 mg per day). After the 12-week period, body weight, body mass index (BMI), waist circumference, body fat mass and subcutaneous fat area were significantly lower in the high catechin group, as compared with the low catechin control group.9
A similar study had been carried out to find the effect of high catechin intake on obese or nearobese Japanese children. One group was given 576 mg of catechins per day and compared with a low catechin group (75 mg per day) after 24 weeks. In addition to assessing the effect on weight reduction, cardiovascular risk factors were also monitored. It was concluded that the ingestion of catechin-rich beverages ameliorates serious obesity and cardiovascular disease risk factors.10
Another interesting area of research was whether tea has any additive effect on exercise induced weight loss programmes. In such a study carried out in US, 132 overweight or obese adult participants were randomly assigned, to receive tea containing 625 mg of catechins with 39 mg caffeine or a control beverage (39 mg caffeine, no catechins) for 12 weeks. Findings of the study was that tea catechin consumption enhances exerciseinduced reduction in abdominal fat. Further, this experiment proves that catechins in the absence of caffeine also could contribute to the reduction of fat.11
Another similar research had focused on the effect of tea on body fat reduction in women. This study investigated the effects of green tea consumption, combined with exercise program on body composition in women, who were overweight or obese. Thirty-six women were divided into four groups (group 1 green tea; group 2 placebo; group 3 green tea plus resistance training; group 4 placebo plus resistance training). After eight weeks the groups receiving tea had reduced body fat and waist circumferences compared to the respective control groups. Further, the third group receiving tea and resistance training had the highest increase in lean body mass (body weight minus body fat) and muscle strength.12
Population studies using a large number of individuals have also proven the effect of tea on weight reduction.
A study carried out in US, examined the association between tea consumption and
weight status of a sample of 6,472 adults, who participated in the 2003–2006 National Health and Nutrition Examination Surveys (NHANES). According to the results, hot tea consumption was inversely associated with obesity, and tea consumers had lower mean waist circumference and lower body mass indices. However, for iced tea consumers, the association was reversed and increased iced tea consumption was associated with higher body mass index and greater waist circumference.
Most of the iced teas available in the market contain significantly low polyphenolic content, compared to a hot cup of tea. Further, most iced teas were sweetened with high amounts of sugar. Findings of this research study demonstrate that the health benefits of tea consumption may occur only when tea is consumed in the traditional manner and iced tea may provide no health benefit to consumers, especially when sweetened.13
A research study carried out in Netherlands investigated the association between flavonoid intake and body mass index, over a 14-year period, in 4280 individuals aged 55–69 years. Findings revealed that body mass index of women with the lowest intake of flavonols/flavones and total catechins increased by 0.95 and 0.77, respectively, after 14 years. Women with the highest intake of total flavonols/flavones and total catechins experienced a significantly lower increase in BMI of 0.40 and 0.31, respectively. The conclusion was that flavonoid and catechin intake may contribute to maintaining body weight in the general female population.14
Results from the research studies on weight loss by green tea has been reviewed by scientists in the Maastricht University, Netherlands. Results of 11 studies reviewed revealed that Catechins or catechin-caffeine mixture have a positive effect on weight loss and weight maintenance.15
Recent Systematic Reviews on Tea Consumption and Weight Reduction
Caffeine in tea could increase the metabolic rate in humans and therefore increase the energy expenditure, thus contributing to weight reduction. Recently, attention has been focused on other components in tea in relation to weight reduction. Systematic review of such research had concluded that epigallocatechin-3-gallate (EGCG) also has the potential to increase the metabolic rate and therefore increase the energy expenditure, contributing to weight reduction. 16
Fifteen research studies carried out to evaluate effect of tea on body fat and body weight in humans have been reviewed recently. Conclusion of the review was that daily consumption of tea has shown effectiveness on body fat and body weight reduction. The effectiveness is greater when the period of tea consumption was 12 weeks or more.17
Another systematic review examined research done up to May 2019, on body weight and related parameters, to find the effect of herbal extracts on these parameters. One of the findings was that green tea resulted in a significant reduction in weight, body mass index, waist circumference, hip circumference and total cholesterol.18
In a similar systematic review, on human clinical research studies carried out on obese persons to find the effect of tea consumption, revealed that tea consumption could reduce body weight, Body Mass Index (BMI) and waist circumference. The effects were more pronounced when the duration of tea consumption was 12 weeks or more. Based on the results the authors suggest that the use of tea can be combined with a balanced and healthy diet, and regular physical exercise in the management of obese patients.19
Recent reviews of human clinical trials on the tea consumption and weight and related parameters, show that regular tea consumption for a long time contributes to weight reduction and related parameters, such as waist circumference in both healthy and obese people.
Conclusions
Tea, without milk and sugar, contains almost zero calories. Therefore, the consumption of a plain cup of tea between main meals instead of snacks could significantly contribute to maintain weight and weight reduction. Flavonoids in tea assists weight maintenance through several mechanisms. These include reduced fat absorption from the digestive tract, increased energy expenditure by increasing the rate of metabolism and, also, alterations in fat metabolism resulting in reduced synthesis and storage. Population studies involving large numbers of individuals, also indicate that regular tea consumption has a positive effect on weight maintenance. Further, research on consumption of tea while undergoing an exercise regime for weight reduction, had shown synergistic effects on weight maintenance. Recent reviews of human clinical trials on the tea consumption and weight and related parameters show that regular tea consumption for a long periods of time has pronounced effects on weight reduction.
ɇ Obesity and excess weight have become significant global problems, as they could lead to Non-Communicable Diseases such as heart disease, stroke, diabetes and cancer.
ɇ A cup of tea, without milk and sugar, contains almost zero calories. Therefore, a cup of plain tea instead of any other food could significantly contribute to weight reduction and weight maintenance.
ɇ Tea components, especially flavonoids, could contribute to weight reduction by reducing fat absorption from the digestive tract, and altering the fat metabolism in the human body.
ɇ Research on individuals following an exercise regime for weight reduction has shown that tea consumption has an additive effect on the weight loss.
ɇ Human clinical trials and also population studies in several countries, involving large numbers of individuals, had demonstrated that tea consumption could contribute to weight reduction and weight maintenance.
ɇ Regular tea consumption for a long periods of time has more pronounced effects of weight reduction.
REFERENCES
1. Fact sheet on obesity and overweight, 2016, World Health Organization, Available at: www.who.int/mediacentre/factsheets/fs311/en/, Accessed on 22nd August 2022
2. Facts and Figures on childhood obesity, 2014, World Health Organization, Available at: www.who.int/end-childhood-obesity/facts/en/, Accessed on 22nd August 2022
3. Yuda, N., Tanaka, M., Suzuki, M., Asano, Y., Ochi, H., Iwatsuki, K., 2012, Polyphenols extracted from black tea (Camellia sinensis) residue by hot-compressed water and their inhibitory effect on pancreatic lipase in vitro., Journal of Food Science, 77, H254–H261.
4. Walkowiak, J., Bajerska, J., Kargulewicz, A., Lisowska, A., Siedlerski, G., Szczapa, T., Kobelska-Dubiel, N., Grzymisławski, M., 2013, Single dose of green tea extract decreases lipid digestion and absorption from a test meal in humans. Acta Biochimica Polonica, 60, 481–483.
5. Reza Rastmanesh, 2011, High polyphenol, low probiotic diet for weight loss because of intestinal microbiota interaction, ChemicoBiological Interactions, 189 (1–2), 1–8.
6. Yang CS, Zhang J, Zhang L, Huang J, Wang Y, 2016, Mechanisms of body weight reduction and metabolic syndrome alleviation by tea, Molecular Nutrition and Food Research, 60(1), 160-74.
7. Takuji Suzuki, Monira Pervin, Shingo Goto, Mamoru Isemura and Yoriyuki Nakamura, 2016, Beneficial Effects of Tea and the Green Tea Catechin Epigallocatechin-3-gallate on Obesity, Molecules, 21 (10), 1305 – 1318
8. Rains TM, Agarwal S, Maki KC, 2011, Antiobesity effects of green tea catechins: a mechanistic review, Journal of Nutritional Biochemistry, 22(1), 1-7.
9. Tomonori Nagao, Yumiko Komine, Satoko Soga, Shinichi Meguro, Tadashi Hase, Yukitaka Tanaka, and Ichiro Tokimitsu, 2005, Ingestion of a tea rich in catechins leads to a reduction in body fat and malondialdehyde-modified LDL in men, American Journal of Clinical Nutrition, 81, 122–129
10. Takeshi Matsuyama, Yuriko Tanaka, Isamu Kamimaki, Tomonori Nagao and Ichiro Tokimitsu, 2008, Catechin Safely Improved Higher Levels of Fatness, Blood Pressure, and Cholesterol in Children, Obesity, 16, 1338–1348.
11. Kevin C. Maki, Matthew S. Reeves, Mildred Farmer, Koichi Yasunaga, Noboru Matsuo, Yoshihisa Katsuragi, Masanori Komikado, Ichiro Tokimitsu, Donna Wilder, Franz Jones, Jeffrey B. Blumberg and Yolanda Cartwright, 2009, Green Tea Catechin Consumption Enhances Exercise-Induced Abdominal Fat Loss in Overweight and Obese Adults, Journal of Nutrtion, 139, 264–270.
12. Cardoso GA, Salgado JM, Cesar Mde C, Donado-Pestana, 2013, The effects of green tea consumption and resistance training on body composition and resting metabolic rate in overweight or obese women, Journal of medicinal food, 16(2), 120-127.
13. Jacqueline A. Vernarelli and Joshua D. Lambert, 2013, Tea consumption is inversely associated with weight status and other markers for Metabolic Syndrome in U.S. adults, European Journal of Nutrition, 52(3), 1039–1048.
14. Laura AE Hughes, Ilja CW Arts, Ton Ambergen, Henny AM Brants, Pieter C Dagnelie, R Alexandra Goldbohm, Piet A van den Brandt, and Matty P Weijenberg, 2008, Higher dietary flavone, flavonol, and catechin intakes are associated with less of an increase in BMI over time in women: a longitudinal analysis from the Netherlands Cohort Study, American Journal of Clinical Nutrition, 88, 1341–1352.
15. Hursel R, Viechtbauer W, Westerterp-Plantenga MS, 2009, The effects of green tea on weight loss and weight maintenance: a metaanalysis, International Journal of Obesity, 33(9), 956-961.
16. Mahendra P Kapoor et al, Physiological effects of epigallocatechin-3-gallate (EGCG) on energy expenditure for prospective fat oxidation in humans: A systematic review and meta-analysis, Journal of Nutritional Biochemistry, 2017 May;43:1-10, doi: 10.1016/j. jnutbio.2016.10.013
17. Lucía Cristina Vázquez Cisneros et al, Effects of green tea and its epigallocatechin (EGCG) content on body weight and fat mass in humans: a systematic review, Nutricion Hospitalaria, 2017 Jun 5;34(3):731-737, doi: 10.20960/nh.753
18. Moloud Payab et al, Effect of the herbal medicines in obesity and metabolic syndrome: A systematic review and meta-analysis of clinical trials, Phytotherapy Research, 2020 Mar;34(3):526-545, doi: 10.1002/ptr.6547
19. Ying Lin et al, The effect of green tea supplementation on obesity: A systematic review and dose–response meta-analysis of randomized controlled trials, Phytotherapy Research, 2020 Oct;34(10):2459-2470, doi: 10.1002/ptr.6697
Summary
History of Tea and its Medicinal Properties
According to legend, tea was discovered by the Chinese Emperor Sheng Nung in 2737 B.C. Tea was confined to the Chinese Royal circles, initially, spreading to the common Chinese population only around 6th century A.D. Tea was introduced to Europe in the 17th century and in the 19th century and large commercial plantations were established in Asian countries, especially in Ceylon (Sri Lanka) and India, which then were British colonies. Historically, from the outset and till the beginning of the 19th century, tea was considered to be largely of medicinal value, useful in the alleviation of many ailments. Thereafter, tea had become the most consumed beverage in the world, second only to water and considered more as a pleasant beverage, with medicinal benefits becoming secondary. However, from the 1980s onwards there has been a renewed interest in the beneficial properties of tea, with wide-ranging scientific research in centres around the world, confirming, through modern research, the age-old beliefs in the health benefits of the brew.
Types of Tea
Black, green and oolong are the main types of tea produced in the world. Black tea is the commonest, accounting for approximately 78% of the global production, followed by green tea at about 20% and oolong tea only 2%. All these types of tea are produced from the tender shoots of the tea plant (Camellia sinensis), the differences
in the final product being brought about by the variations in processing methods. A review of the results from scientific studies on the beneficial effects of different types of tea reveal that they have similar health benefits.
Herbal teas are not produced from the tea plant (Camellia sinensis). Therefore, the effects of consumption of herbal teas are quite different to that of real tea. Unlike with tea, effects of most herbal teas on human health have not been extensively studied. Generally a prefix (usually name of the plant), is used when referring to herbal teas (e.g. chamomile tea, peppermint tea etc.)
Nutritional Value of Tea
Carbohydrates, Protein, Lipid (fat), Vitamins, Minerals and Water are considered the basic nutrients in food, essential for good health. The content of carbohydrate, protein and fat, the energy or calorie providers, is minimal in tea. However, in the modern-day context, with most individuals struggling to control daily calorie intake, this is an advantage. If such individuals opt for a high quality tea and develop the habit of drinking a plain cup of tea between main meals, instead of consuming snacks, it will significantly contribute towards weight reduction.
Thiamin and folate are components of the vitamin B family and drinking three cups of tea could contribute to approximately 5% of the daily requirement. Other vitamins present in tea do not make significant contributions towards daily intake.
Manganese is the most predominant mineral in tea and consumption of one liter of tea contributes to 45% of the daily requirement. Very low sodium content (less than 0.05% of the daily requirement from one litre of tea), distinguishes tea from other beverages which have either high natural or added sodium. Sodium is a component of salt (scientific termSodium Chloride). High sodium (or salt) intake is implicated in the development of high blood pressure and, therefore, food advisory authorities in many countries have started salt reduction programs. Hence, tea would be an ideal beverage, suitable for individuals with high blood pressure or individuals at risk of developing high blood pressure.
Since water is the main component (> 99%) in a cup, tea consumption contributes to the hydration of the body and could be used as a beverage to obtain part of the daily fluid requirement.
Chemical Composition of the Tea Brew
A critical appraisal of the components in the brew is important, as they would enter our body through the digestive tract and could impart either beneficial or deleterious effects. Major components in both black and green brews fall into the class of chemical compounds known as polyphenols, and the sub class known as flavonoids. Flavanols (commonly called catechins), theaflavins and thearubigins are the main compounds present in tea that come under flavonoids. Green tea mainly contains catechins and in black tea, most of the catechins are
converted to theaflavins and thearubigins during processing. Modern research has demonstrated the beneficial effects of plant flavonoids. Tea being one of the plants having uniquely high amounts of flavonoids compared to other plant based dietary items therefore could significantly contribute to improving human health. These compounds also mainly contribute to the typical colour of the brew and taste in both green and black tea. The other components in black and green tea brew are similar in composition.
Caffeine and theanine are other important components of both black and green tea. Flavonoids, caffeine and theanine are biologically active (ability to have an effect inside a living organisms), which contribute to the beneficial effects of tea. Unlike major nutrients, even relatively small amounts (milligram quantities) of biologically-active compounds could impart beneficial effects inside human body.
Antioxidant Activity of Tea
Majority of early scientific studies on tea were focused on antioxidant activity, as antioxidants are known to exert beneficial effects in humans through several mechanisms. Tea flavonoids have been established as antioxidants in vivo (inside a living organisms) in human clinical trials. Although all plants contain flavonoids, the uniqueness of tea is that it contains very high amounts of flavonoids compared to other food items. Hence, antioxidant activity of tea is very high compared to other food items. Although recent research has established many other mechanisms through which tea flavonoids impart
beneficial effects, antioxidant activity remains the most important mechanism.
Comparison of Flavonoid Content in Flavonoid Rich Food
and diabetes. Therefore, it is important that inflammation is controlled quickly once the responsible agent is eliminated. Further, exposure to environmental toxins and toxicants such as smoke, dust particles, pesticides, mycotoxins, polychlorinated biphenyls (PCBs) and toxic metals could also trigger inflammation. As exposure to such agents are common in the present day environment, anti-inflammatory compounds derived from the diet could play an important role in mitigating the adverse effects of inflammation.
Anti-Inflammatory Activity of Tea
Inflammation is a part of the response by the human immune system against pathogens, toxic substances, or injury. Through a series of steps referred to as immune response, the immune system attacks the organisms and other toxic substances that invade the body and cause disease. During injury also the immune system is activated to prevent the entry of harmful microorganisms and other harmful substances. Some of these reactions result in inflammation. Signs of inflammation are heat (rise in body temperature), redness, swelling, pain and change in blood composition. Although essential, excessive or prolonged inflammation could damage the human body and increase the risk of Non-Communicable Diseases (NCDs) such as heart disease, stroke
Scientific research has found that tea polyphenols have anti-inflammatory properties. Therefore, tea consumption could mitigate the adverse effects of inflammation. During inflammation, production of free radicals and other harmful substances take place in the human body, designed to destroy invading pathogenic micro-organisms. However, the prolonged presence of these species harm the human body itself. Antioxidants in tea could neutralise these free radicals and harmful substances, and limit the adverse effects of inflammation, thereby reducing the risk of NCDs such as heart disease, stroke and diabetes, where the development of the disease is associated with inflammation.
Immune Enhancement by Tea
Through a series of steps, collectively referred to as the immune response, the immune system attacks the organisms and other toxic substances that invade the body and cause disease. During injury also the immune system is activated to prevent the entry of harmful micro-organisms and other harmful substances.
An array of plants and their components have immune-modulating properties. Related research has identified that plant polyphenols are an important class of compounds, which enhance immunity. As tea contains uniquely high amounts of polyphenols compared to other plants, many research studies have focused attention on the immune enhancing effects of tea. In addition, theanine in tea also contributes to immune enhancement. Immune enhancement is brought about by modulating the complex signalling processes during the immune response and enhancing the activity of certain immune cells. In addition, recent research has demonstrated that tea polyphenols improve immunity, by increasing the beneficial micro-organisms in the gut and also in the lungs. Therefore, regular tea consumption could enhance immunity and may have prophylactic activity against infectious diseases.
Antiviral Effects of Tea
Infectious diseases have severely affected humans for centuries. As most viral diseases have no effective drugs yet, effects of naturally occurring compounds have been studied for a long time, to find their ability to prevent or reduce the effects of diseases caused by viruses. Tea and its components also have received attention in these efforts. Early work has been focused on the effects of tea or its components on Influenza A and B, Hepatitis B and C and herpes simplex viruses. Recently, attention has been focused on the possibility of using tea components for prophylaxis, or treatment against COVID19. These studies have strongly indicated that tea components, especially EGCG and theaflavins, have the ability to interfere with the replication
process of the viruses inside the host. As the viral replication process increases the severity of the disease, tea has been suggested as a prophylactic agent against viral disease. Further, attention has been focused on developing antiviral drugs from EGCG and theaflavins.
Effect of Tea on the Function of Brain and Mood
Caffeine and theanine are two components in tea which could pass through the ‘blood-brain barrier’ (barrier that selectively allow the components in the blood to enter brain) and enter brain cells.
Caffeine is a well-known Central Nervous System (CNS) stimulant, which enhances alertness and relieves tiredness. The refreshing effect and relief from fatigue after a cup of tea is mainly due to caffeine, though there are concerns regarding the advisability of ingesting excessive amounts of caffeine. A comprehensive review on the safety of caffeine, by the European Food Safety Authority (EFSA), has recommended an upper limit of 400 mg of caffeine per day. Caffeine content in six cups of tea is well below this limit and therefore consumption of six cups of tea would not affect the health of the consumer.
Research has shown that theanine could act on the brain and promote relaxation without inducing drowsiness. Tea is the only plant that naturally contains theanine and, therefore, the only food item with theanine. Recent research on the effect of the unique combination of caffeine and theanine, naturally found only in tea, on brain function, indicates that it improves the cognitive
function (involving all aspects of perception, thinking, reasoning, and memory), enabling an individual to carry out a given task quicker and with greater accuracy. Therefore, tea would be an ideal beverage for consumption during a work break, to refresh, relieve fatigue and improve efficiency.
Recent research on caffeine and theanine has focused on the effect of tea, which contain both, on anxiety, stress and sleep quality. Review of such research has concluded that tea, specially theanine in tea, contributes to reduction of anxiety, stress and improvement in sleep quality.
Research has also demonstrated that polyphenols and caffeine in tea may have protective effects against dementia and Alzheimer’s disease, as they could play a role in reducing neuro-degradation and amyloid plaque formation in the brain.
Tea Consumption and Reduction of the Risk of Non-Communicable Diseases
Types of Studies Carried out on Tea
A large number of research studies have been carried out on the properties and beneficial effects of tea, and results are published in ‘peer reviewed’ (process of subjecting an author's scholarly work, research, or ideas to the scrutiny of others who are experts in the same field, before publishing in a journal or as a book) scientific journals. If a search is done on the US National Library of Medicine data base (PubMed), using the key word ‘tea’, more than 40,000 records could be found. These studies fall into the following categories:
ɇ In vitro (outside a living organisms or in a test tube) studies
ɇ In vivo (inside a living organisms) studies on animal models and humans
ɇ Human clinical trials
ɇ Epidemiological (the branch of medicine which deals with the incidence, distribution, and possible control of diseases and other factors relating to health) studies using large human populations
All types of studies reveal important information. In vitro or studies in a test tube often assist in establishing, whether tea components possess a particular property such as antioxidant activity. In vivo studies assist in establishing whether a property observed under in vitro conditions, is actually observed inside animals and humans. An indication of the magnitude of the effect could also be ascertained. Animal model experiments often provide further information, on the mechanisms in operation inside the body to impart beneficial effects.
Human clinical trials, consisting of a ‘test’ group, which is subjected to a treatment (tea), and a control group which is given a placebo (a substance that has no therapeutic effect to be used as a control, water in this instance) are, thereafter, evaluated for effects on health. Epidemiological research studies deal with the incidence, distribution, and possible control of diseases and other factors relating to health in large populations. Such studies often help in ascertaining whether a particular action (tea consumption), has an effect on the development of a particular disease.
Interpretation of Results from Scientific Studies
To find an answer to a specific question, such as, whether tea consumption could reduce the risk of developing heart disease; a comprehensive review should be carried out, of all the available literature published in scientific journals related to the question. This is called a ‘systematic review’ of scientific literature. Only a qualified scientist working in the particular area of study could carry out such an extensive ‘systematic review,’ which would correctly find the answer to the specific question. Such ‘systematic reviews’ are also published in scientific journals. Therefore, conclusions should be made using such reviews only, where a large number of research studies, carried out in independent laboratories around the world, are considered in arriving at the conclusion.
Incorrect Interpretation of Results from Scientific Research in Popular Media
Often, popular media, including blog sites, deliver conclusions on the effects of food items based on a single research study, which could be misleading. Only a ‘systematic review’ of multiple research studies would provide correct conclusions on the effects of a food item on humans. There are many instances where incorrect information on tea is also given in such media, especially in blog sites on the internet. Therefore, information from such sources should be digested with caution. It is important to identify the original source of information in such instances (which is often not made available), to verify the accuracy of the conclusions.
Information from ‘Internet Scientists’ Internet has provided us an opportunity to convey our thoughts and opinions to others freely. Many individuals maintain blog sites, and Youtube channels, to convey their thoughts and opinions. In recent times, many individuals use these to convey their thought and opinions on the effects of food items on human health. They would categorise food items as bad or good according to their opinion. Further, they also make comparisons between food items. The majority of authors of such sites pose as scientists or medical practitioners. As mentioned above, information from such sources should be digested with caution. A true scientists or a medical practitioner would obtain the information from reliable sources. As mentioned above, meaningful conclusions on the effects of a food item on human health could be made only after a systematic review of all available scientific information. Any genuine scientist or medical practitioner would make the sources of information, from where he obtained information, available to the reader. If the sources are not revealed, generally the information given would merely be his/her thoughts or opinions. Further, some of these blog sites and Youtube channels may be purposely promoting or discrediting a particular food item. Therefore, it is always better to obtain information on topics, such as effect of a food item on human health, from sources where original scientific research has been carried out to arrive at the given conclusions. It is prudent to give a wide berth to internet sources which do not provide original sources of information.
Effect of Tea Consumption in Relation to Non-Communicable Diseases
Systematic review of the scientific literature reveals that regular tea consumption reduces the risk of many Non-Communicable Diseases. Polyphenols in tea are mostly responsible for the beneficial activities and they reduce the risk of development of diseases through several mechanisms.
Tea Consumption and Diabetes
Diabetes has become a major global health issue. There are two types of diabetes. Type 1 is caused by inadequate production of insulin, which controls the blood sugar levels. In Type 2 diabetes, generally, adequate amounts of insulin are produced but the response of the cells to insulin is compromised. Therefore, taking up of sugars by the cells is reduced, thus increasing blood sugar levels. Research has shown that regular consumption of tea could have an effect on Type 2 diabetes (90% of the diabetes is of this type) through several mechanisms.
Tea consumption could reduce glucose absorption into the body from the digestive tract, especially from carbohydrate rich food. Tea flavonoids also have the ability to increase the sensitivity of insulin, the hormone which controls blood glucose levels. Further, tea consumption could have indirect effects on diabetes, through the reduction of inflammation and obesity. These two are the main risk factors for diabetes and they also contribute to increased diabetic complications.
Population studies on tea consumption and risk of diabetes also reveal that tea consumption could reduce the risk of Type 2 diabetes.
Tea Consumption, Heart Disease and Stroke
According to the World Health Organization (WHO), the leading cause of death at present is heart disease, with 17.9 million deaths in 2019, whilst stroke is the number two cause.
A large number of research studies carried out on the effects of tea on heart disease indicate that flavonoids in tea act through several mechanisms, to reduce the risk of heart disease and stroke. These mechanisms include, lowering of blood lipids (fat), by reduced absorption from the digestive tract and reduction of the oxidation of lipids by the antioxidant flavonoids in tea, which would reduce their deposition on arteries.
Improvement of the endothelial function of the arteries by tea improves the expansionconstriction function of the arteries when necessary, thus assisting to maintain blood pressure constant. Low sodium (or salt) content in tea also makes it a beverage suitable for regular consumption, as high salt intakes could lead to high blood pressure. Reduction of inflammation and blood clotting by tea flavonoids also contribute to the lowering of the risk of heart disease. Lowering of the risk of diabetes by tea indirectly contributes to the reduction of the risk of heart disease.
Population studies carried out using large populations to determine the risk factors for heart disease also confirm that tea consumption reduces the risk of heart disease.
Tea Consumption and Cancer
Results from a very large number of research studies on tea and cancer indicate that certain components in the tea brew, especially flavonoids found in both black tea and green tea, act through several different mechanisms to reduce the risk of cancer. Tea flavonoids are helpful in all the stages of the cancer development process. Tea flavonoids could bind with most commonly found carcinogens in the environment and neutralise them, in vivo, thus reducing the risk of initiation of cancer.
Production of free radicals and other toxic molecules by carcinogens and radiation also contribute to the cancer initiation process. Antioxidant flavonoids have the ability to neutralise such harmful species. Tea components have the ability to inhibit both the progression of cancer and the process of metastasis (spread of cancer from one part of the body to another part through blood stream).
Further, a large number of population studies, using cancer patients and healthy individuals with a similar life-style as control, have been carried out to ascertain the effect of tea consumption on cancer in different parts of the human body. These studies also indicate that tea consumption reduces the risk of cancer in different parts of the human body.
Tea Consumption, Oral and Digestive Tract Health
A large number of microorganisms live in the digestive tract of the humans, both beneficial and harmful. Another set of microorganisms known as ‘commensal microorganisms,’ also present in the human system, have neutral properties. Regular dietary items have an effect on the populations of these microorganisms. A review of results from studies on tea consumption and microorganisms of the digestive tract, indicate that it generally results in the reduction of harmful microorganism populations, whilst increasing the beneficial microorganism populations. This would result in the improvement of oral health due to reduced tooth decay and lowered risk of oral diseases, such as oral candidiasis caused by harmful micro-organisms. Further, risk of gastritis and peptic ulcers caused by the harmful micro-organisms in the stomach and intestine will also be reduced.
Tea Consumption and Weight Reduction
Tea without milk and sugar contains almost zero calories. Therefore, consumption of a plain cup of tea between main meals, instead of snacks, could significantly contribute to weight management and weight reduction. Further, flavonoids in tea helps in weight maintenance through several mechanisms. These include reduced fat absorption from the digestive tract, increased energy expenditure by increasing the rate of metabolism and also alterations in fat metabolism, resulting in reduced synthesis and storage. Population studies involving large
numbers of individuals also indicate that regular tea consumption has a positive effect on weight maintenance. Further, research on consumption of tea whilst undergoing an exercise regime for weight reduction has shown synergistic effects on weight maintenance.
Recommendations of Food Advisory Authorities
Food advisory authorities in many countries of the world carry out systematic reviews of scientific data on dietary items consumed by the people of specific countries. Based on these findings, they issue dietary guidelines to maintain good health for the people in that country. The recommendations would be to restrict some of the dietary items which cause harm, whilst encouraging the consumption of those which improve health. The Health Council of the Netherlands has reviewed the data on tea and confirmed that tea consumption could improve human health. Accordingly, they have made a recommendation to ‘drink three cups of tea daily,’ in the Dutch dietary guidelines, 2015 (Dutch dietary guidelines are reviewed periodically and the last review was in 2015). (www.gezondheidsraad.nl/sites/default/ files/201524edutch_dietary_guidelines_2015.pdf)
Overall Effect of Tea Consumption on Human Health
Tea drinking hydrates (provides water) the body. Therefore, tea could be consumed to provide part of the daily requirement of fluids. Extensive research on tea has not found adverse effects of
regular tea consumption. It has been established that tea consumption could improve the antioxidant defences in the human body. Further, research has established that tea consumption could contribute to the lowering of the risk of NCDs, such as heart disease, stroke, cancer and diabetes. It can improve the oral and digestive tract health and contribute to weight reduction. Due to the action of caffeine and theanine, a cup of tea could refresh you and improve your performance, making it an ideal beverage for the work place. Therefore, tea could be considered as a prudent choice to provide part of the daily requirement of fluids.
Frequently Asked Questions
What is Real Tea?
Real tea is the product made using the tender shoots of the ‘tea plant’. The botanical name of the tea plant is Camellia sinensis.
Tea in its true sense is defined by the International Standards Organisation (ISO) as, “tea derived solely and exclusively, and produced by acceptable processes, notably withering, leaf maceration, aeration and drying, from the tender shoots of varieties of the species Camellia sinensis, known to be suitable for making tea for consumption as a beverage.”
What are the Major Types of Real Tea?
Depending on the method of processing, different types of real tea are obtained as the final product. Major types of real tea are black tea, green tea, oolong tea and white tea. Black tea is fully fermented or aerated tea and green and white tea are non-fermented or non-aerated tea. Oolong tea is partially-fermented or partially-aerated tea (See chapter 2 for details on types of tea).
What are the Differences Between ‘Orthodox Black Tea’ and ‘CTC Black Tea’?
In black tea processing, either ‘orthodox’ or ‘CTC’ methods could be used for the rolling process. Products obtained from the two processes are referred to as ‘orthodox black tea’ and ‘CTC black tea’. Orthodox production method is used in Sri Lanka while the other two major black tea producing countries, India and Kenya, use the CTC method which produces tea, generally very uniform in taste. Orthodox processing allows for adjustments by the ‘tea maker’ to enhance the inherent character and taste of the tea. Production of volatile compounds and, therefore, aroma is generally better in orthodox black tea. Therefore, connoisseurs of tea prefer orthodox black tea, as it is better in quality and offers subtle variations to satisfy any consumer. Hence “Ceylon Tea” produced in Sri Lanka has a greater demand and also fetches higher prices.
What is Meant by Grades of Tea?
After processing, the major types of tea mentioned above are graded according to particle size. Orthodox black tea processing could produce up to 20 grades. Main grades are known as Orange Pekoe (OP), Broken Orange Pekoe (BOP), Broken Orange Pekoe Fannings (BOPF) and Dust (D). OP has the largest particle size whilst Dust grade has the smallest particle size. CTC processing generally produces smaller particles and have a lesser number of grades. Main grades are Broken Pekoe (BP), Broken Orange Pekoe (BOP), Pekoe Fannings (PF) and Dust (D).
Are Genetically-Modified (GM) Tea Plants Used to Produce Tea?
At present, genetically-modified tea plants are not used by tea producing countries. Therefore, it is free of any genetically-modified organisms (GMO). The Tea Research Institute of Sri Lanka has taken a policy decision not to produce any genetically modified tea varieties. Therefore, ‘Ceylon Tea’ will remain GMO free in the future too.
What are Herbal Infusions (Herbal Tea)?
In certain instances the term ‘tea’ is used to identify the products made from plants other than the tea plant (Camellia sinensis). According to the International Standards Organisation (ISO) definition, tea should be solely and exclusively derived from the tea plant (Camellia sinensis). Therefore, the correct term for products made from other plants would be ‘Herbal Infusions’ or Tisanes. Chamomile, peppermint, hibiscus and rosehip are examples for herbal infusions.
Which Has More Health Benefits, Herbal Infusions or Real Tea?
Herbal teas are not produced from the tea plant (Camellia sinensis). Therefore, the effects of consumption of herbal teas are quite different to that of tea. Generally, a prefix (usually name of the plant), is used when referring to herbal teas (e.g. chamomile tea, peppermint tea, etc.) Unlike with real tea, effects of most herbal teas on human health have not been extensively studied. Large amount of research, especially human clinical trials on ‘real tea’ enables proper scrutiny of the
results through systematic reviews, to arrive at correct and meaningful conclusions. However, when it comes to herbal teas the health effects announced are sometimes based on very few studies or a single study. The majority of these studies are generally either in vitro studies (carried out in a test tube), or animal model studies which cannot be extrapolated to predict what happens inside human body. Only very few human clinical trials have been conducted, making it difficult to arrive at meaningful conclusions on the effect of these on human health.
Although consumption of certain herbal teas could impart beneficial effects, it is very difficult to come to clear conclusions on the effect of regular consumption of herbal teas on human health on the basis of currently available knowledge. Therefore, it is prudent to restrict consumption of herbal teas to occasional use.
On the other hand, any type of ‘real tea’ made from the tender shoots of the tea plant (Camellia sinensis) could be considered as the most suitable beverage for regular consumption which is of proven health benefits to humans.
What is ‘Ceylon Tea’ and Why is it Different from Other Tea?
Ceylon tea refers to tea produced in Sri Lanka (Ceylon is the name used for the country during the colonial era). Sri Lanka produces black tea and Ceylon black tea is considered qualitatively superior to tea produced in other countries. This perception is reflected in the higher prices obtained for Ceylon tea at the tea auctions.
Over the years the country has focused attention on producing teas of the highest quality. Major reasons for the better quality of Ceylon tea are the following:
ɇ climatic and weather conditions that prevail in the tea-growing regions
ɇ the unique variations of climatic conditions between sub regions of tea-growing areas,
ɇ unique tea varieties developed for plantations in these sub regions
ɇ manual harvesting which allows the selection of the most suitable shoots
ɇ orthodox processing method used, which permit changes to enhance the natural taste and aroma of the tea
These factors, in combination, enables Sri Lanka to produce different types of tea that would satisfy the taste preferences of any consumer in the world.
What makes Tea a Healthy Beverage?
The major water soluble components in tea are known as polyphenols. Scientific research has demonstrated that plant polyphenols could produce beneficial effects inside the human body. Whilst all plants contain polyphenols, the uniqueness of tea is that it contains very high amounts (as much as 40% of water soluble components) of polyphenols. In addition, caffeine and theanine in tea also contribute to beneficial effects. Caffeine could make an individual alert and give relief from fatigue, while theanine could give a relaxing mood. Both caffeine and theanine, a combination found only in tea, could improve the performance of an individual while in a relaxed mood.
A large number of scientific research studies have been carried out on the effects of tea brew and individual components of tea, on human health. These studies have demonstrated that regular tea consumption could improve human health. These effects are discussed in detail in the relevant chapters of the book.
Are the Health Benefits of Black and Green Tea Similar?
The main difference between black tea and green tea is that green tea contains catechin as the main type of polyphenols, whilst in black tea these are converted to theaflavin and thearubigins. All the other components are similar in both types of tea. Large number of research studies have been carried out on the health benefits of black and green tea brews and their individual components. Review of the results of these studies indicate that both types of tea have similar health benefits. However, the number of research studies on green tea are far greater than that of black tea. The reason is that most of the research studies on tea have been carried out in Japan and China, which produce green tea. Green tea has been used for these studies, resulting in a greater number of publications on the beneficial effects of green tea, than the number of publications on the beneficial effects of black tea. Therefore, there is a perception among some that green tea is better than black tea for human health. However, more recently, a large number of research studies have been carried out on the health benefits of both black and green tea in non-tea producing countries. The results of these studies indicate that black and green tea have similar health benefits.
Is There a Difference in Health Benefits Between Cold Brewed Tea and Hot Brewed Tea?
Health benefits of tea depend on the amount of beneficial components extracted into the cup. Cold brewing results in reduced extraction of these beneficial components. Therefore, beneficial effects of a hot brewed tea would be more compared to a cold brewed tea. Generally, commercially-available Ready to Drink Tea, which is intended for use as a cold beverage, also contains a diluted solution compared to a hot cup of tea. Therefore, health benefits from a traditional hot cup of tea would be comparatively high.
Does the Addition of Milk and Sugar Reduce the Health Benefits of Tea?
Addition of milk and sugar does not alter the health benefits provided by the tea components. However, diabetic patients should monitor the amount of sugar consumed. Further, addition of either sugar or milk will add calories to the cup of tea, which contains almost zero calories. Calorie conscious individuals should take note of this fact.
Does Tea have a Diuretic Effect and Therefore Lead to Fluid Loss from the Body?
Caffeine in tea is a mild diuretic (diuretics increase the volume of urine). Therefore, in the past there was a concern that tea drinking could lead to water loss from the body. Recent research has established that the amount of caffeine found
in tea does not lead to a significant increase in the volume of urine. Therefore, tea drinking does not lead to fluid loss from the body. The amount of water in a cup of tea actually contributes to the hydration (supply of water) of the body. Therefore, tea could be used to obtain part of the fluid requirement per day.
What is Caffeine and what are the Amounts of Caffeine in Tea?
Caffeine is the central nervous system stimulant present in tea. After consumption, caffeine makes a person alert and it also relieves fatigue. Therefore, a cup of tea could refresh a person especially if the person is tired.
A typical high quality cup of tea contain approximately 40-50 mg of caffeine although the range could vary between 20 to 90 mg. The higher amounts of caffeine in high quality tea is due to proportionately higher amounts present in the bud, as compared to the first leaf. Caffeine content declines with leaf maturity, therefore, the second leaf would have lower amounts of caffeine than the first leaf. As high quality teas have higher proportions of bud and the first leaves, the caffeine content in high quality tea would be comparatively higher.
Are the Caffeine Levels in Black, Oolong, Green and White Tea the Same?
Generally, the cultivars used for green tea processing contain lower levels of caffeine than in cultivars used for black tea processing. Therefore,
green tea could contain relatively less amounts of caffeine. However, there could be exceptions as many other factors, such as plucking standards, also influence caffeine levels.
Oolong tea could be produced using cultivars intended for both green tea and black tea production. Therefore, oolong tea could contain varying amounts of caffeine.
White tea is generally produced using only the buds. As bud contains the highest amount of caffeine compared to the leaves (caffeine content decreases with leaf maturity), white tea would contain higher amounts of caffeine.
What are the Safe Levels of Caffeine for Consumption?
There have been many scientific reviews on the caffeine safety and maximum levels, that should be ingested per day. According to the most comprehensive review, carried out by the European Food Safety Authority (EFSA) in 2015, single doses of caffeine up to 200 mg (about 3 mg/ kg body weight for a 70-kg adult) do not result in any negative effects. Further, habitual caffeine consumption up to 400 mg per day also does not result in any negative effects in adults.
What are Safe Levels of Caffeine for Pregnant and Lactating Mothers?
Caffeine could pass through the placenta of a pregnant mother to the foetus. Therefore, there are concerns about using caffeinated beverages during pregnancy. The EFSA report has found that only very high doses of caffeine, which could not be achieved by consuming tea, could have an
effect on the foetus. However, as a precaution, they have recommended restricting daily caffeine intake to 200 mg per day during pregnancy. Further, caffeine could pass from lactating mothers to the baby. Therefore, the EFSA report advice to restrict caffeine intake for lactating mothers also to 200 mg per day.
What are the Safe Levels of Caffeine for Children?
EFSA report has recommended the maximum intake of caffeine for children, as 3 mg/kg of body weight, which also is the maximum intake recommended for adults in one sitting. The weight of the child has to be taken into account when calculating the maximum intake of caffeine per day for children. For example, a child with 50 kg body weight could consume a maximum of 150 mg of caffeine per day (3 mg/kg body weight x 50 kg), which is equivalent to 3 cups per day.
What is Decaffeinated Tea?
De-caffeinated teas are intended for individuals with a sensitivity to caffeine. Caffeine has been removed in the decaffeinated teas. However, small amounts (< 6 mg) of caffeine could still remain in de-caffeinated tea.
What is Theanine and what are the Beneficial Effects of Theanine?
Theanine is a unique non-protein-forming amino acid. The tea plant is the only agricultural crop that contains theanine. Therefore, theanine is not present in any other plant based food or beverage except tea. Tea leaves contain 1-2% of theanine on a dry weight basis.
Scientific experiments have demonstrated that theanine ingestion increases the alpha wave production in the brain, which indicates that the brain is in a relaxed state. Further, alpha waves indicate that the alertness is not reduced and that the individual is not drowsy.
In addition, research has shown that theanine has a neuro-protective effect and also acts as a cognitive enhancing agent. (Cognition is the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses.)
Theanine has an effect on the attention level/ awareness of an individual and therefore, results in better performance when a particular task is given. Further, theanine was found to reduce anxiety and stress, thus inducing relaxation. Owing to these effects theanine in tea was found to improve the creative problem solving ability of individuals. Therefore, overall, theanine in tea would both relax the individual and improve performance.
In addition, recent research has demonstrated that theanine reduces anxiety, stress and improves sleep quality.
Is Tea Gluten Free?
Gluten is a protein composite found in wheat and related grains, including barley and rye. It is not present in tea.
Is Tea Lactose Free?
Lactose is a sugar derived from milk. It is not present in tea.
Is Tannic Acid Present in Tea?
Tannic acid is not present in tea. Tannins are plant polyphenolic compounds which could be used for the tanning process (conversion of raw hide into leather). In the past, structures of most polyphenolic compounds in plants had not been identified. Therefore, in certain instances, all plant polyphenols had been referred to as tannins although some, including tea polyphenols, did not possess the tanning ability. However, structures of most plant polyphenols have now been identified and named (e.g. catechins, thearubigins and theaflavins in tea). Therefore, generally at present, the word tannin is not used for plant polyphenols.
How much Theophylline, a Compound Known to have an Effect on Easing Asthma, is Contained in a Cup of Tea?
Theophylline is an alkaloid which acts as a mild broncho-dilator, or causes widening of the bronchi (airways in the lungs), thus giving alleviation from asthma. In brewed tea, trace amounts of theophylline is present, which are significantly less than a therapeutic dose. Tea has classically been used to treat mild asthma and bronchitis. Although other potent anti-asthma medications are available with more therapeutic benefit, tea may be beneficial for mild respiratory problems and is safe even for children. But tea should not be used as a medication for asthma.
Both black and green tea contain similar amounts of theophylline.
Are There any Allergens in Tea?
Tea does not contain any known allergens. Therefore, tea consumption does not lead to allergies.
Does Tea Affect Iron Absorption from the Digestive Tract?
Tea does not affect the absorption of iron, known as “haem iron,” found in meat and fish, However, tea could affect the absorption of iron from plant sources (vegetables and fruit) known as ‘non haem’ iron when they are present together in the digestive tract. If the diet is rich in meat or fish which contain relatively high amounts of iron, meal-time tea drinking would not affect the iron status in the body. However, if the diet is mainly vegetarian and already marginally deficient in iron (it should be noted that vegetarian diets also could be rich in iron), tea should be consumed either 1 ½ hours before or after meals.
Why Does Tea Cloud When it is Cooled?
Clouding in tea is a result of the colloidal precipitate that is formed, called ‘tea cream’. Tea creaming takes place when a hot cup of black tea is cooled below 400 C. A weak complex is formed between caffeine and polyphenols (theaflavins and thearubigins). The tendency to cream down varies from tea to tea. If the creaming down is high, that particular tea is regarded as high quality tea.
What is Tea Scum or the Dark Skin on top of the Brewed Tea?
Scum formation is due to the presence of high amounts of calcium in the water (hard water) used for brewing tea. Therefore, scum formation could be avoided by using soft water for brewing. Further, it should be noted that tea scum is not harmful to human health.
How Should Tea be Stored to Retain Freshness?
Tea should be stored in a cool and dry place, in an air tight container made out of suitable barrier material, away from light sources and heat, preferably in a refrigerator.
Tea being a hygroscopic substance readily absorbs water from its surroundings. Tea quality deterioration on storage was found to accelerate with high relative humidity and heat and it is for this reason that storage in cool and dry conditions is essential. Further, tea could absorb volatile compounds (that gives a smell) from the surroundings. Therefore, it should not be stored together with other, odorous food items,
What are the Nutritional Benefits of Tea?
Major Nutrients in Tea
Major nutrients in the diet are carbohydrates (starch and sugar), proteins and fat. These are required as fuel for energy production and as ‘building blocks’ in maintaining the structural integrity of the human body. Tea provides only negligible amounts of these major nutrients and
therefore calorific value of tea is very low. This is an advantage in the present-day context as a large proportion of the global population exceeds the recommended daily calorie intakes. A plain cup of tea between main meals, without any snacks, could significantly contribute to the restriction of the daily calorie intake and limit weight gain.
Minerals and Vitamins in Tea
Minerals and vitamins are the other important nutrients. Mineral content in tea and the recommended daily intakes are given in the table below. Low sodium content is a notable feature of tea. High sodium increases the risk of high blood pressure and therefore most countries
Other Constituents
Source: USDA National Nutrient Database for Standard Reference Release 28: Report Date:January 25, 2016 *DRI - Dietary reference intakes, US Nutrient recommendations, Source: National Institute of health, Office of dietary supplements, *ND - Not defined
Black
have started salt (salt is sodium chloride and the harmful element in it is sodium) reduction programmes for their populations, as it has been found that a large proportion of the global population exceeds the recommended salt intake. Therefore, tea would be an ideal beverage to reduce the risk of high blood pressure.
Three cups of tea provide approximately 5% of the daily requirement of thiamine and folate (which are components of the vitamin B family). Tea contains varying amounts of other vitamins also. However, their contribution to the recommended daily intakes is not significant.
Does Tea Consumption Have an Effect on Inflammation?
Inflammation is a part of the response by the human immune system against pathogens, toxic substances or injury. Through a series of steps referred to as immune response, the immune system attacks the organisms and other toxic substances that invade the body and cause disease. During injury also the immune system is activated to prevent the entry of harmful microorganisms and other harmful substances. Some of these reactions result in inflammation. Signs of inflammation are heat (rise in body temperature), redness, swelling, pain and change in blood composition.
Although essential, excessive or prolonged inflammation could damage the human body and increase the risk of Non-Communicable Diseases, such as heart disease, stroke and diabetes. Therefore, it is important that inflammation is
controlled quickly, once the responsible agent is eliminated. Further, exposure to environmental toxins and toxicants such as smoke, dust particles, pesticides, mycotoxins, polychlorinated biphenyls (PCBs) and toxic metals could also trigger inflammation. As exposure to such agents are common in the present-day environment, anti-inflammatory compounds derived from the diet could play an important role in mitigating the adverse effects of inflammation.
Scientific research has found that tea polyphenols have anti-inflammatory properties, without compromising the role of the immune system. Therefore, tea consumption could mitigate the adverse effects of inflammation. During inflammation, the production of free radicals and other harmful substances take place in the human body, to combat invading pathogenic microorganisms. However, prolonged presence of these harm the human body itself. Antioxidants in tea could neutralise these free radicals and harmful substances, and reduce the adverse effects of inflammation, thus reducing the risk of NonCommunicable Diseases such as heart disease, stroke and diabetes, where the development of the disease is associated with inflammation.
Does tea Consumption have an Effect on Diabetes?
Regular consumption of tea could have an effect on Type 2 diabetes (90% of the diabetes is of this type) through several mechanisms. Research reveals that tea consumption could reduce the glucose absorption into the body from the digestive tract, especially from carbohydrate
rich food. Type 2 diabetes is mainly caused by the ineffectiveness of insulin, the hormone that controls blood glucose, rather than inadequate production of insulin. Tea flavonoids have the ability to increase the effectiveness of insulin.
Tea consumption could also have indirect effects on diabetes through the lowering of inflammation and obesity. These two are the main risk factors for diabetes and they also contribute to increased diabetic complications. Population studies on tea consumption and risk of diabetes, in which very large populations who consume tea are compared with a control population with similar lifestyles, also reveal that tea consumption could reduce the risk of Type 2 diabetes.
Does Tea Consumption Have an Effect on Heart Disease and Stroke?
Heart disease and stroke are the leading causes of death in the world at present. Narrowing of arteries due to plaque formation could restrict the blood supply to the heart and brain. Complete blockage of the already narrowed arteries due to blood clots cause heart attacks and stroke. Several risk factors are involved in the plaque formation in the arteries. The risk factors include high cholesterol and fat levels in blood, high blood pressure, diabetes, oxidative stress, inflammation and factors that favour blood clotting.
Detailed research on tea consumption and the above risk factors, have revealed that flavonoids in tea have the ability to reduce the effects of these risk factors. In addition, epidemiological studies carried out in several countries, where large numbers of individuals from populations
have been followed for a long period of time, have revealed that regular tea consumption could reduce the risk of heart disease and stroke. As plaque formation is a slow process taking several years, individuals could adopt healthy lifestyles and diets that reduce the risk. Regular tea consumption could be a part of a heart healthy diet.
Does Tea Consumption have an Effect on Cancer?
Cells are the smallest units or building blocks of tissues and organs in the human body. Alterations in the cells could result in abnormal cells, with uncontrolled proliferation, leading to the formation of cancerous tissue. Alterations in the cells are initiated by damage to DNA in the cells, which control all cellular processes. The damage is usually caused by carcinogenic substances or harmful radiation, such as UV light. Research has demonstrated that flavonoids in tea has the ability to neutralise cancer causing substances, and reduce the risk of cancer initiation. Harmful radiation causes the formation of potential carcinogenic substance in the human body. Tea flavonoids have the ability to neutralise these harmful substances also.
Once cancer is initiated in a cell, it develops into a malignant cancerous tissue through several stages. Research has also shown that tea flavonoids could interfere with these processes through several mechanisms, and reduce the risk of formation of a malignant cancer.
Metastasis is the process, where cells from a malignant cancer migrate to other parts of the
body, through the blood circulatory system, and establish a cancer in another part of the body. Metastasis greatly diminishes the effectiveness of conventional cancer therapy. Research has also shown that tea flavonoids reduce the risk of metastasis.
In addition, a review of a large number of population studies, where cancer patients and healthy individuals with similar lifestyles were compared, to identify the factors that influence the carcinogenesis process, has revealed that tea consumption reduces the risk of cancer.
Does Tea Consumption have an Effect on Oral and Digestive Tract Health?
The human digestive tract consists of the oral cavity, pharynx, oesophagus, stomach, small intestine and large intestine and other related organs, that work together, through the digestion process, to convert food into basic nutrients that could be absorbed into the body. Large populations of microorganisms live in all parts of the digestive tract. Some of these microorganisms are beneficial to the humans while some others are harmful. ‘Commensal microorganisms’ that live in the digestive tract are neither harmful nor beneficial to the humans. Different dietary items have different effects on these microorganisms.
Some dietary items known as ‘prebiotics’ could increase the beneficial microorganism populations. Choosing such dietary items for regular consumption would contribute to improve the overall health of the individual. A large number of research studies have been carried
out to find the effect of tea consumption on the microorganism populations in the digestive tract. Review of results from these studies reveal that regular tea consumption results in the reduction of harmful microorganism populations, whilst increasing the beneficial microorganism populations.
Main effects observed due to this activity are, improvement of oral health by reducing tooth decaying bacteria. In addition, high fluoride content in tea helps in the incorporation of fluoride into the teeth, making it more resistant to tooth-decaying bacteria. Tea also has the ability to reduce the population of organisms such as Candida, which cause inflammation of the oral cavity (oral candidiasis).
The presence of large populations of harmful micro-organisms, such as Helicobacter pylori in the stomach and intestines, significantly contribute to the development of gastritis and peptic ulcers. These ulcers have the potential to develop into cancers. Research has demonstrated that regular tea consumption could reduce the populations of harmful micro-organisms, including Helicobacter pylori, thus reducing the risk of development of gastritis, peptic ulcers and cancer in the digestive tract.
Does Tea Consumption Have an Effect on the Brain Function and Mood?
Caffeine and theanine in tea are the constituents that have an effect on the central nervous system. Caffeine is a well-known stimulant that could make you alert and relieve fatigue.
Theanine also has effects on the central nervous system, mainly to induce relaxation. Caffeine is known to stimulate a person and improve his performance and also improve the speed of carrying out a given task. Recent research has found that theanine also has similar effects and, together, theanine and caffeine have synergistic effects. Therefore, tea, the only beverage in which both caffeine and theanine are present together, could improve performance, whilst keeping a person in a relaxed mood. Therefore, tea is an ideal beverage to refresh a person, as well as to prepare him for work.
Further, polyphenols and caffeine in tea may have protective effects against dementia and Alzheimer’s disease, as they could play a role in reducing neuro-degradation and amyloid plaque formation in the brain.
Does Tea Consumption Have an Effect on Weight Loss and Obesity?
Worldwide, obesity has more than doubled since 1980 and become an important global health issue. Excess weight and obesity are major risk factors for a number of chronic diseases, including diabetes, cardiovascular diseases and cancer. Therefore, any measures that could be used for weight reduction would be very important.
Research has demonstrated that tea consumption could contribute to weight loss and weight maintenance. A cup of tea, without milk or sugar, contains almost zero calories. Therefore, consumption of a cup of plain tea between main meals, instead of any other snacks,
would significantly contribute to weight maintenance. Further, research had shown that tea consumption could contribute to weight reduction through many other mechanisms. These include reduced fat absorption from the diet, alterations in fat metabolism resulting in lower storage of fat and increased energy expenditure resulting in increased use of fat. Many human clinical studies and population studies involving a large number of individuals have also confirmed that tea consumption contributes to lowering obesity and weight maintenance.
Effect of Tea on Celiac Disease
Celiac (Coeliac) disease (gluten-sensitive enteropathy), is an immune reaction to gluten, a protein found in wheat, barley and rye. In celiac disease patients, consuming gluten containing food triggers an immune response in the small intestine. Over time, this reaction damages small intestine's lining and prevents it from absorbing some nutrients (malabsorption). The intestinal damage often causes diarrhea, fatigue, weight loss, bloating and anemia and can lead to serious complications.
Although tea possesses anti-inflammatory properties and could reduce ‘oxidative stress,’ which processes are involved in the aetiology of celiac disease, until recently the effect of tea on celiac disease has not been evaluated. Digestion of gliadin (which is a component of gluten) results in the production of immune-stimulatory peptides which initiate immune response in the small intestine. A recent study has found that green tea extract inhibited gliadin digestion, thus
reducing the risk of celiac disease. Further, it has been found that tea catechins could ameliorate the tissue damage in the intestine. Although not conclusively proven yet, tea appears to ameliorate the effects of celiac disease. Therefore, probably, tea could be included in a diet aimed at celiac disease patients.
Does
Flavoured Tea have the Same Health Benefits as Non-Flavoured Tea?
Flavoured teas are produced by adding a flavour to tea. Generally very small quantities of flavour are added to tea and in preparation of a cup of tea similar quantities of tea is used. Therefore, flavoured tea has the same health benefits as nonflavoured tea.
Is Tea an Adaptogen?
Recently health conscious individuals have focused their attention on adaptogens. Adaptogens are defined as natural substances that can help us to adapt to stress and anxiety. In addition, they may relieve fatigue whilst promoting overall wellbeing. Research has shown that theanine in tea could reduce stress and anxiety. Caffeine in tea relieves fatigue (see chapter 13 for details). Further, research has shown that tea consumption could reduce the risk of major Non-Communicable Disease and improve the wellbeing of an individual. Therefore, tea is a natural beverage that possesses all the qualities of an adaptogen.
Can Tea be Taken on an Empty Stomach in the Morning?
Healthy individuals can consume a cup of tea on an empty stomach. In fact, a large percentage of world population start its day with a cup of tea and thoroughly enjoys it. However, there could be individuals who will feel uncomfortable with any beverage on an empty stomach. Acid secretion in the stomach is the main cause for this. When we consume any food item or beverage, acid will be secreted in the stomach, as part of the digestion process. This might cause discomfort in a small percentage of individuals and an empty stomach would aggravate the sensation. The addition of milk and sugar to tea is known to minimise acid secretion and such individuals could try that. Another option is to try different types of teas, such as lighter liquoring teas (lighter in colour), to find a tea more suitable to people with such sensitivity.
Although tea induces acid secretion in the stomach, research has proven that regular consumption of tea can reduce the risk of chronic gastritis. (see chapter 12 for more details)
How to Brew a Perfect Cup of Tea
The preparation of a cup of tea is very important, to get the best quality out of the tea used. Important elements in preparing a good cup of tea are
ɇ Quality of tea used
ɇ Quality of water used
ɇ The brewing technique.
Selection of Tea
Tea could be selected based on individual taste preferences. To a discerning consumer, the method of plucking and processing of tea would be important criteria to consider when choosing the tea. Hand plucking of tea ensures the selection of the most tender parts for processing and orthodox processing ensures the enhancement of the inherent character of tea.
Orthodox processing also enables the differentiation of subtle variances between processing centres and the production of a wide spectrum of tea types, each different from the other, providing the consumer with a very wide choice. Approximately 2.5 g or a spoonful of tea in a pot should be used to prepare a single cup of tea.
Storage of Tea
Tea is hygroscopic (readily absorbs moisture) and, similarly, absorbs odours or fragrances. Therefore, after opening a pack, tea should be stored in an airtight container and kept away from moisture, heat, light and odours. It should be stored in a cool and dry place.
When purchasing, consumers should also pay attention to the packaging of the tea. Packaging should be airtight and the packaging material should be able to exclude light and odours. Triple laminated aluminium foil with such properties is the commonest packaging material for tea. When made tea comes out of the processing factory, the moisture content is around 3-4%. Prolonged storage in bulk form and operations such as
blending in the open could result in the increase in the moisture level and the deterioration of tea. Therefore, teas packed at origin generally reach the consumer without any deterioration.
Water
Fresh, colourless and odourless water, just brought to boil, should be used for brewing. Soft water (containing 10 -120 mg/L of calcium and magnesium) with pH close to neutral is best i.e. pH = 7 (pH 6 to 8 is suitable). Re-boiled water should not be used for brewing, as repeated boiling removes most of the dissolved air, affecting the taste.
Chlorinated tap water could affect the taste of tea. Therefore, if either taste or odour indicates the presence of chlorine, such water should not be used for preparation of tea.
Brewing Black Tea
Approximately 2.5g, or a spoonful of tea should be used per cup of tea. Tea should be placed in a pre-heated tea pot (tea pot could be preheated by swirling in warm water) and freshly boiled water should be added to the pot. When water is brought to boil, it should be immediately added to the pot without delay, so that the water temperature is not reduced by the time it is added to the pot (95-100°C).
Allowing adequate time for extraction with intermittent stirring is very important. Three to five minutes is required for extracting all the components into the brew from a good quality tea. If the particle size of tea is large five minute
brewing is required, whilst for smaller particles, three minutes is adequate. Shorter brewing times will result in an inferior cup of tea.
Stirring enhances the extraction process. Therefore, with black tea, stirring immediately after pouring the boiling water, and stirring after brewing for one minute, and stirring again before serving, results in enhanced extraction and a better cup of tea.
Brewing Green Tea
When brewing green tea, generally lower temperatures (70-80°C) and shorter duration of brewing (2-3 minutes), is more suitable.
Brewing Speciality Tea
For speciality teas, different brewing conditions might be required to obtain the best cup. In such instances the manufacturer’s recommendations should be followed.
Tea in the 21st Century
Tea was first discovered as a medicine and then became the beverage prized by emperors and nobility, a herb justly described by ancient poets as an elixir. As tea evolved into an affordable luxury, it acquired its undisputed relevance in the 21st Century for the unique health benefits that tea offers are only a part of its allure.
Fine tea is a special luxury, for each sip of tea brewed from handpicked leaves of Camellia sinensis is the outcome of the work of artisans, with every subtle fragrance, flavour and character reflecting an aspect of nature. Soils, moisture, sunlight, temperature, the variation of each over time – all influence taste, appearance and fragrance in tea, with the art of the tea picker and teamaker only acting as the master craftsman would in tuning an instrument, but never dominating or determining the outcome.
Tea is also social, symbolising friendship, family and stimulating conversation around the world. As you learn of the potent human health benefits in tea, please remember that protection from disease is only one of several dimensions that tea embodies. Its purity is beautiful in presenting nature, whilst the expertise that tea demands in its production extends that sophistication to the art and passion of the men and women who are engaged in handpicking and handmaking tea.
Tea is undoubtedly a 21st Century herb, for this combination of health, natural, social and artisanal aspects is more relevant to our lives today than ever before. And then there is more. Tea is considered traditional, but it is traditional only when it is treated traditionally. The spectrum of colour in real tea, the array of fragrances, flavours, strength and mouthfeel that tea offers, all evolving constantly, is an unmatched palette for the skill of the mixologist and culinary artist. With respect for the provenance of each tea, the possibilities for sharing the pleasure in tea through gastronomy and mixology are limited only by imagination, skill and creativity. In this way, the tradition of high tea becomes an engaging and luxurious culinary experience, and tea in the morning, afternoon or evening, indulgent and pleasing.
“Tea urges tranquility of the soul.”
William Wordsworth Longfellow (1807-1882)
For centuries, problems of mankind have been solved over a cup of tea whether they were problems between nations, amongst businesses, even in families, between husbands and wives, tea has been the soothing balm that helped their solution. The simple act of pouring a cup of tea is, in itself, an ice-breaker, providing pleasurable anticipation of the goodness that is to follow. I have dedicated my life towards providing that cup: not only to solve problems but to add sunshine, to our day, with every sip of Dilmah.
