Tea (Camellia sinensis Theaceae) is indigenous to Asia, specifically China. Its ancient history dates back to 2737 BC when the Chinese Emperor Chen-Nung accidentally discovered an infusion containing wild tea bush leaves remarkably reviving. Since the fourth century AD tea has been an integral part of life in China and a major feature of important ceremonies. It spread to Japan in early 1400 AD and evolved to the "tea ceremony," a ritual central to Japanese culture. Tea was introduced to Europe when the French East India Company brought tea to Holland in 1610, France in 1636 and England in 1650.

Major tea growers of the world include India, China, Sri Lanka, Korea, parts of Africa and South America. In the United States, tea was very popular with the early colonials and a valuable source of income to the British government. In 1773, as an act of protest against high taxes on tea, the British tea cargo was dumped in the ocean resulting in the famous "Boston Tea Party."

Tea is an evergreen tree that can grow to a height of over 10 meters; it is trained as a bush and frequently pruned to maintain a height of ~1.5m for effective plucking and crop management. The tea plants bear dark glossy green leaves and white flowers. The tender buds (pekoe) are harvested with two terminal leaves and processed to obtain the commercial tea.

Three major categories of tea derived from C. sinensis by differential processing methods are: the black teas (fermented), the oolong teas (semi-fermented) and the green teas (unfermented). The longer the fermentation process, the more caffeine contained in the final product. Black tea is popular in India and manufactured in two ways- orthodox and "crush-tear-curl" (CTC) method. The orthodox method involves rolling the tea leaves in a machine to break and release the phytochemicals where as the CTC method uses a CTC machine to crush and break the leaves.

In Chinese medicine tea is one of the fundamental herbs used in treating illnesses. The leaves are used as diuretic and a stimulant. They exert an influence over the nervous system, giving a feeling of comfort and exhilaration. Tea is also used internally in the treatment of diarrhea, hepatitis and gastroenteritis, and externally to treat cuts, burns, bruises, insect bites and swellings. Excessive tea drinking can lead to dizziness, constipation, indigestion, palpitations and insomnia due to caffeine contents.

The active constituents promoting good health in tea are polyphenols, particularly the catechin called epigallocatechin gallate (EGCG) (1). A typical cup of tea prepared in a proportion of 1 g leaf to 100 mL water in a 3-min brew normally contains about 30-42% catechins and 3-6% caffeine (2). Other "herbal" teas are made of leaves of plant species other than C. Sinensis and may not contain any catechins. Tablets and capsules containing extracts of polyphenol EGCG are available, some of which provide up to 97% polyphenol content- equivalent to drinking four cups of tea.

Research demonstrates that green tea protects against cardiovascular disease in many ways- lowers total cholesterol levels and improves the cholesterol profile (the ratio of LDL cholesterol to HDL cholesterol), reduces platelet aggregation, and lowers blood pressure (3-6). The polyphenols in green tea have been shown to be effective antioxidants (7), and to lessen the risk of cancers of several sites, stimulate the production of several immune system cells, and have antibacterial properties-specifically against the bacteria that cause dental plaque (8-10). Reportedly, tea drinking can also offer protection against liver damage (11) and osteoporosis(12).

References
1. Graham 1992. Green tea composition, consumption, and polyphenol chemistry. Prev. Med. 21:334-350.
2. Balentine et al. 1997. The chemistry of tea flavanoids. Crit. Rev. Food Sci. Nutr. 37: 693-704.
3. Kono et al. 1992. Green tea consumption and serum lipid profiles: A cross-sectional study in Northern Kyushu, Japan. Prev. Med. 21:526-531.
4. Yamaguchi et al. 1991. Preventive effects of green tea extract on lipid abnormalities in serum, liver and aorta of mice fed an atherogenic diet. Nip Yak Zas. 97:329-337.
5. Sagesaka-Mitane et al. 1990. Platelet aggregation inhibitors in hot water extract of green tea. Chem. Pharm. Bull. 38:790-793.
6. Stensvold et al. 1992. Tea consumption. Relationship to cholesterol, blood pressure, and coronary and total mortality. Prev. Med. 21:546-53.
7. Serafini et al. 1996. In vivo antioxidant effect of green tea in man. Eur. J. Clin. Nutr. 50:28-32.
8. Stoner et al. 1995. Polyphenols as cancer chemopreventive agents. J. Cell. Bioch. 22:169-80.
9. You 1993. Study on feasibility of Chinese green tea polyphenols (CTP) for preventing dental caries. Chin. J. Stom. 28:197-99.
10. Hamilton-Miller 1995. Antimicrobial properties of tea (Camellia sinensis L.). Antimicro Agents. Chemother. 39:2375-77.
11. Imai and Nakachi 1995. Cross sectional study of effects of drinking green tea on cardiovascular and liver diseases. BMJ 310:693-696.
12. Hegarty et al. 2000. Tea drinking and bone mineral density in older women. Am. J. Clin. Nutr. 71:1003-1007.

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