Its said that tea drinking originated about 3000 years ago when a few leaves accidentally fell into a cup of hot water held by a Chinese emperor. The emperor found the brew tastier than plain water and he subsequently recommended it as a remedy for various ailments. Others claim tea originated in India and became popular with Buddhist monks who helped introduce the calming but refreshing drink throughout Asia. Tea was introduced to Europeans by Turkish traders in the 6th century and it later became an important part of Dutch and British trade.

There are many other types of tea but in this article I am covering only the dried leaves of Camellia sinensis. Depending on how the leaves are processed, the resulting tea is classified as black, green, red or yellow and white. Black tea in the context of this article refers to the process of drying and fermentation and is the common tea we drink in Australia, taken with or without milk. Until recently, it was considered that milk reduced absorption of important therapeutic tea compounds but its now accepted that adding milk does not impair teas benefits (European Journal of Clinical Nutrition, 52; 356-9: 1998).

Green tea is non-fermented and is the most scientifically researched and probably the most therapeutic of all the teas. However, all the Camellia teas contain similar constituents and studies confirm they also have therapeutic effects. Oolong tea (sometimes called red or yellow tea) is widely consumed in southern China and is produced by partial fermentation.

To make the rarer white teas, the leaves and buds are generally steamed before drying. Its called white tea because the buds are covered with silvery hairs that produce a pale yellowy brew. Its slightly sweet and more palatable than green tea. A premium white tea may also be made from the downy unopened buds that are left to wither naturally, but this product is very expensive and requires a 15-minute soaking time.

There are many taste differences in teas, depending on the maturity of the leaves, soil type and climate, as well as processing methods and added flavourings. Jasmine tea, for instance, is usually a mix of green and black teas plus some jasmine flowers for flavouring.

Tea constituents

The main therapeutic compounds are referred to as tea polyphenols, catechins or flavonoids. As a group, they are powerful antioxidants that reduce damage to fats, protein and cells as well as having various anti-cancer effects (Journal of Nutrition, 130; 472-8S: 2000).

L-theanine gets broken down in the body to ethylamine, which helps gamma delta T immune cells (Proceedings of the National Academy of Sciences, 100; 6009-14: 2003). In this study, five cups of black tea daily significantly increased the blood levels of interferon, a natural compound that helps fight a variety of infections. L-theanine also stimulates production of alpha waves, creating feelings of relaxed alertness. In addition, L-theanine stimulates both GABA, a neurotransmitter that reduces anxiety, and serotonin, a mental wellbeing chemical.

Due to the tiny amounts of the tea plant that are actually consumed, the quantities of essential nutrients in all types of teas are insignificant and you should look to a healthful and varied diet as your main source of these nutrients. However, one survey in Europe found that tea was a richer source of flavonoids than vegetables and fruits. In common with all plants, tea contains literally hundreds of compounds but these are consumed in such tiny quantities that its unlikely the majority of them have any measurable effect in the body.