Camelia sinensis is an evergreen shrub or tree, long cultivated in China but now also elsewhere, maintained by pruning and for ease of harvesting to a height of 2-4 feet (0.6-1.2m). Green tea is produced by lightly steaming the freshly cut tealeaves, while to produce black tea the leaves are allowed to oxidize. The reason for the well known beneficial activity of green tea by comparison to black tea, is that steaming inactivates the enzymes, which on oxidation convert the rich stores of polyphenols to compounds with much reduced activity. The major polyphenols of green tea are flavonoids, such as catechin, epicatechin, epicatechin gallate, epigallocatechin gallate, and a number of proanthocyanidins. Other compounds in green tea are caffeine, theophylline, an unusual amino acid called theanine, proteins, organic acids, lignin and chlorophyl.
- Anticancer. Most of the studies on green tea have been focused on cancer-causing and cancer-prevention aspects. Green tea polyphenols are powerful antioxidants offering greater protection than vitamins C and E. In addition, green tea compounds may increase the activity of antioxidant and detoxifying enzymes, such as glutathione peroxidase, glutathione reductase, glutathione S-transferase, catalase, and quinone reductase, in the small intestine, liver and lungs. Further, in vitro experiments have shown that green tea polyphenols inhibit cancer by blocking the formation of such cancer-causing compounds as nitrosamines; they detoxify or trap cancer-causing agents; and suppress the activation of existing carcinogens. This is cancer protection indeed. One of the reasons for the low cancer rates among the Japanese, seems to be the consumption of green tea. The forms of cancer best prevented by green tea are cancers of the alimentary canal, including stomach, small intestine, pancreas and colon, lung cancer, and estrogen related cancers including breast tumors.
- Anti-allergic. Various flavonoids in green tea, like other flavonoids such as the PCOs of grape seed extract (see above), have been shown to inhibit the release of histamine, which is the major chemical mediator in allergic reactions,
- Anti-microbial. Evidence also suggests that green tea has a potent activity against harmful bacteria. This is most probably due the direct effect of catechins, and to the indirect effect of raising the levels of glutathione peroxidase.
- Antioxidant. The antioxidant properties of green tea are largely due to the radical scavenging polyphenols, especially to epigallocatechin galate (EGCG) and gallic acid. In addition, as previously discussed green tea compounds raise the activity of glutathione peroxidase and several other antioxidant enzymes, thus providing a solid basis for antioxidant activity.
- Thermogenic. Green tea compounds such as caffeine and theophylline have been shown to enhance the rate of fat metabolism. However, increasing fat metabolism would invariably increase the free radicals produced in the body. Green tea can raise fat metabolism without the danger of excess free radicals, because of the excellent antioxidant protection offered by its polyphenols. And although coffee contains even higher amounts of caffeine, and hence potentially a better agent of fat metabolism, it also contains harmful roasted hydrocarbons which are potent free radical sources, and does not have anything that even remotely approaches the antioxidant properties of green tea.
Note: Persons sensitive to caffeine may use decaffeinated green tea, which possesses all the above attributes save the increase in fat metabolism.