Green Tea (lu cha)

What is green tea? What is it used for?

After water, tea is the second most commonly consumed beverage in the world. The most frequently consumed variety of green tea, which, along with its black and oolong counterparts, is derived from the plant camellia sinensis. Different-colored teas are produced depending on how the leaves of the plant are prepared.

The origins of tea as a beverage remain something of a mystery, although it has been drunk for thousands of years. One of the most popular legends concerns a Chinese emperor, who "discovered" the drink when leaves from a tea tree accidentally fell into a cup of hot water he was drinking. Whatever the origins may be, tea remains extremely popular, not only as a beverage, but as an increasingly important component of health and well-being.

Green tea contains a variety of chemicals and compounds, including several volatile oils, minerals, vitamins and caffeine. The chemicals of most importance in green tea are polyphenols, which are believed to be responsible for most of the green tea's positive benefits.

The known health benefits associated with green tea are numerous. Studies conducted over the past two decades have shown that green tea and green tea extracts are effective in treating conditions ranging from high blood cholesterol levels and tooth decay to atherosclerosis and some types of cancer. Other evidence suggests that green tea can play a role in the promotion of weight loss and improvements in the immune system.

How much green tea should I take?

The amount of green tea to be drunk depends on the condition being treated. Most research conducted in the past decade is based on an average of three cups of green tea (approximately 750 milliliters) per day. However, other studies have suggested that upwards of 10 cups (2,500 milliliters) is necessary to achieve an optimal effect from green tea and its polyphenols. The typical cup of green tea combines one teaspoon of tea leaves with approximately 250 milliliters of water, steeped for a minimum of three minutes.

What forms of green tea are available?

Dozens of types of green tea, along with dozens of black and oolong teas, can be found at supermarkets, Asian markets, specialty stores, health food stores, coffee and tea shops, and herbal shops. Many stores also sell tablets and capsules containing green tea extracts and large amounts of polyphenols. Decaffeinated green tea is also widely available.

What can happen if I take too much green tea? Are there any interactions I should be aware of? What precautions should I take?

Green tea is considered generally safe and free of side-effects. Large amounts of green tea taken for extended periods of time may cause insomnia and anxiety, but these conditions are usually due to the tea's caffeine content and will disappear through reduction or elimination of tea from the diet. Green tea is known to interact with a variety of medications, including atropine, codeine, ephedrine and warfarin; patients taking these medications should consult with a licensed health care provider before taking tea or tea extracts. As always, make sure to consult with a licensed health care provider before taking large amounts of green tea or any other herbal remedy or dietary supplement.

References

• Hamilton-Miller JM. Antimicrobial properties of tea (Camellia sinensis L.). Antimicro Agents Chemother 1995;39:2375-7.
• Imai K, Nakachi K. Cross sectional study of effects of drinking green tea on cardiovascular and liver diseases. BMJ 1995;310:693-6.
• Kohlmeier L, Weterings KG, Steck S, et al. Tea and cancer prevention: an evaluation of the epidemiologic literature. Nutr Cancer 1997;27:1-13.
• Sasazuki S, Komdama H, Yoshimasu K, et al. Relation between green tea consumption and severity of coronary atherosclerosis among Japanese men and women. Ann Epidemiol 2000;10:401-8.
• Stensvold I, Tverdal A, Solvoll K, et al. Tea consumption. Relationship to cholesterol, blood pressure, and coronary and total mortality. Prev Med 1992;21:546-53.