Herb of the Month- Green Tea (Camellia sinensis)

ii: Herb of the Month

Green Tea (Camellia sinensis)

Marianne Hughes, with illustration by Hazel Brady

We associate drinking tea with sociability and hospitality— activities almost completely missing from our lives for over a year now. Though the fact that we have wrapped up warm to meet one friend outside, perhaps with a flask of tea, is testament to the strength of human need this long-established tradition fulfils.

The plant we know as ‘tea’ is indigenous to south-west China, with over 350 cultivars. It has been drunk there for over 3000 years and before that, the leaves were probably chewed. Its origin story is that once, after Buddha fell asleep while meditating, he cut off his eyelids and hurled them to the ground; where they fell, tea plants arose to bestow alertness. Indeed, tea contains about 50mg of caffeine per cup (compared to coffee’s 85mg). It is also made up of 10-24% tannins. The tannins are thought to be a possible cause of oesophageal cancer, though drinking tea with milk eliminates this risk by neutralising the tannins.

In China, spring-harvested leaves are thought to have the best health-giving properties. Two leaf tips and a bud are picked (the bud is not an unopened flower but an immature, unopened leaf). The black tea, with which we are most familiar, is made through a process of fermenting the leaves before drying; for green tea, the leaves are steamed and dried.

Since ancient times, green tea has been used in Asia to treat any type of diarrhoea— an advantage of that tannin content —and also typhoid. In traditional Chinese and Ayurvedic medicine, Camellia sinensis was used to treat asthma as well as vascular and coronary diseases. More recent research (Shen et al, 2009) suggests that green tea can be preventative in osteoporosis, thereby reducing the risk of hip fractures.

In a wide-ranging literature review, Chacko et al (2010) comments on the complex chemical composition of green tea and its specific health benefits, bearing in mind that some of the findings reviewed were from animal studies and some from studies using green tea extract. It would seem that the drying process of green tea preserves higher levels of antioxidant polyphenols than in black tea. This polyphenol content is 30% flavanols, known as catechins. The most abundant catechin is EGCG— epigallocatechin-3-gallate —and it is this substance that has been the focus of many studies. The catechins appear to have a protective effect against heart disease, stroke, a number of cancers, and some degenerative diseases. These effects appear to derive from green tea’s ability to lower blood pressure, lower blood glucose levels, and act as a potent antioxidant. There are some downsides; green tea may have an affinity for iron and so reduce the bioavailability of iron from the diet, and aluminium can accumulate in the tea plant and be transferred to the body.More positively, Gilbert (2019) notes that new research into the mood-enhancing effects of tea drinking shows the EGCG content of green tea is associated with ‘quiet wakefulness with an increase in focus and attention’, and that all tea seems to reduce the stress hormone cortisol.

So, it is not just the ritual of making a cup of tea and seeing a friend that makes us feel better, there is something in the tea, too.

References Bown, D. (2002) Encyclopaedia of Herbs. Dorling Kindersley, London Bynum, H. & W. (2014) Remarkable Plants That Shape Our World. Thames & Hudson, London Chacko, S. M.; Thambi, P. T.; Kuttan, R. & Nishigaki, I. (2010) ‘Beneficial effects of green tea: a literature review’, in Chinese Medicine, 5 (13) Gilbert, N. (2019) ‘The science of tea's moodaltering magic’, in Nature, 566(7742): S8–S9 Shen, C. L.; Yeh, J. K.; Cao, J. J. & Wang, J. S. (2009) ‘Green tea and bone metabolism’, in Nutrition Research 29(7): 437–456 Simmonds, M., et al (2016) The Gardener’s Companion to Medicinal Plants: An A-Z of Healing Plants and Home Remedies. Royal Botanic Gardens Kew, Frances Lincoln, London