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, 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, considered more as a pleasant beverage with medicinal benefits becoming secondary. However, from the 1980s there was a renewed interest in the beneficial properties of tea, with wide-ranging scientific research in centers 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 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 45% of the daily requirement. Very low sodium content (less than 0.05% of the daily requirement from one liter of tea) distinguishes tea from other beverages which have either high natural or added sodium. Sodium is a component of salt (scientific term- Sodium 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 green and black tea brew fall into the class of chemical compounds known as Polyphenols, and the sub class known as Flavonoids. Flavanols (commonly called as catechins), theaflavins and thearubigins, are the main compounds present in black 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. These compounds 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.

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

Water soluble Components Black Tea

Green Tea

Red Wine

Apples Soy Beans (Dry) Tofu

Onions

Blueberries

Tart Cherries

Kale

Leaf Lettuce (mg/serving)

120 - 300 100 - 200 40 - 140 6 - 15 76 - 207 35 - 63 ~28 2 - 36 26 - 33 ~22 ~17

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 (NCD’s) 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. Therefore, tea consumption could mitigate the adverse effects of inflammation. During inflammation, production of free radicals and other harmful substances takes 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 neutralize these free radicals and harmful substances and limit the adverse effects of inflammation, thereby reducing the risk of NCD’s such as heart disease, stroke and diabetes, where the development of the disease is associated with inflammation.

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 recent 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.

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 25,000 records could be found. These studies fall into the following categories.

• In vitro (outside a living organisms or in a test tube) studies • In vivo (inside a living organisms) studies on animal models and humans • Human clinical trials • 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 on 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 deals 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 are considered in arriving at the conclusion.

Incorrect Interpretation of Results from Scientific Research in Popular Media

Often, popular media, including blog sites make 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.

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 increase 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 8.5 million deaths in 2012 whilst stroke is the number two cause.

A large number of research studies carried out on the effect 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 expansion -constriction 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 neutralize 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 neutralize 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 microorganisms. 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 harm, whilst encouraging the

consumption of those which improve health. The Health Council of the Netherlands has recently reviewed the data on tea and confirmed that tea consumption could improve the human health. Accordingly, they have made a recommendation to ‘Drink three cups of tea daily’, in the Dutch dietary guidelines, 2015. (https://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 defenses in the human body. Further, research has established that tea consumption could contribute to the lowering of the risk of NCD’s, 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.