Green Tea
Camellia Sinensis
Chad Bradshaw, Anh Nguyen, and Jeff Surles
General Description:
Green and black tea are both derived from the same plant, the tea plant. This evergreen shrub or tree can grow to a height of 30 feet, but is usually pruned to a height of 2-3 feet. The leaf bud and its two adjacent young leaves along with the stem are used medicinally. An older leaf is considered to be of lower quality.
Green tea is produced by lightly steaming the fresh-cut leaf. Black tea is made by allowing the leaves to oxidize, thereby converting the highly therapeutic polyphenols to less active compounds. These polyphenols have potent antioxidant and anticancer properties.
Chemical Composition:
Green tea contains polyphenols, most importantly flavonoids (catechin, epicatechin, epicatechin gallate, epigallocatechin gallate, and proanthocyanidins). Epigallocatechin gallate is considered the most significant active compound. The leaf bud and the first leaves are the richest in epigallocatechin gallate. Dried green tea leaves generally contain from 8-12% total polyphenols.
Green tea also contains caffeine (3.5%), theanine (~4%), lignin (6.5%), organic acids (1.5%), protein (15%), and chlorophyll (0.5%). One cup of green tea usually contains about 50-100mg of caffeine and 300-400 mg of polyphenols. Preparations that are decaffeinated and concentrated for polyphenols are available.
Pharmacology:
Green tea polyphenols are potent antioxidant compounds. Green tea may also increase the activity of antioxidant enzymes. In one study mice ingested green tea polyphenols for 30 days. Researchers found a significant increase in the activity of glutathione peroxidase, glutathione reductase, glutathione S-transferase, catalase, and quinone reductase (all of which are antioxidant and detoxifying enzymes) in the small intestine, liver, and lungs.
Green tea also blocks the formation of cancer-causing compounds such as nitrosamines, suppresses the activation of carcinogens, and detoxifies and traps cancer-causing agents. Human studies also point to the concept that green tea can prevent some forms of cancer, most specifically GI cancers (stomach, small intestine, pancreas, colon), lung cancer, and estrogen-related cancers including most breast cancers. In vitro studies of breast cancer have shown that green tea inhibits the interaction of tumor promoters, hormones, and growth factors with their receptors, producing growth arrest of the tumor.
Clinical Applications:
Prevention of cancer is the primary clinical application for green tea. Population studies suggest a link between green tea consumption and the much reduced cancer rate in Japan. Consumption of black tea however may actually increase one's risk of cancer, particularly rectal, biliary, and endometrial.
Drinking green tea with meals may inhibit the formation of nitrosamines. Popular Japanese custom is to drink green tea with meals, and may be a major reason for the low cancer rate in this country.
Dosage:
The normal amount of green tea consumed in Japanese culture is about 3 cups/day (240-320 mg polyphenols). For a green tea extract standardized for 80% total polyphenol and 55% epigallocatechin gallate content, this translates to a daily dose of 300-400 mg. Be sure to look for both polyphenol and epigallocatechin gallate contents when purchasing a product.
Toxicity:
Green tea is not linked with any significant side effects or toxicity. Caffeine in the green tea may produce typical stimulant responses.
Clinical Trials:
"Green tea consumption and the risk of pancreatic and colorectal cancers" Int J Cancer. 70(3), 255-258, (1997).
Population-based case-control study conducted in Shanghai of newly diagnosed cancer patients during 1990-1993. Cancer types were as follows: colon (991), rectal (884), and pancreatic (451). Controls were matched to cases by age and gender. Odds ratios were calculated and were adjusted for age, income, education, and cigarette-smoking habits.
For males who consumed > 300 g/month of tea leaves, beneficial effects correlated with rectal and pancreatic cancers, but not colon cancer. For females consuming > 200 g/month of green tea, beneficial effects were seen with all three cancers.
"In vivo antioxidant effect of green and black tea in man" Eur J Clin Nutr, 50(1), 28-32 (1996).
Preliminary in vitro tests showed that green tea inhibited radical formation in a dose-dependent manner. Green tea was 6 times more potent than black tea, and milk had no effect on the antioxidant activity.
In vivo activity was measured using two groups of 5 adults, with a control of 5 people, ingesting 300 mL of either green or black tea. The same group tested on a later day with 300 mL tea + 100 mL milk. Plasma antioxidant potential was measured before and 30, 50, and 80 minutes after the ingestion of the tea. The maximum antioxidant effects were seen for green and black teas at 30 and 50 minutes postingestion. Antioxidant effects were absent with coingestion of milk, presumably due to the complexation of green tea polyphenols with milk proteins.
References:
Mitscher, L.A. et al. "Chemoprotection: a review of the potential therapeutic antioxidant properties of green tea (Camellia sinensis) and certain of its constituents" Med Res Rev 17(4), 327-365 (1994 Jul).
Yam, T.S. et al. "Microbiological activity of whole and fractionated crude extracts of tea (Camellia sinensis) and of tea components." FEMS Microbiol Lett 152(1), 169-174 (1994 Jul 1).
Serafini, M. et al. "In vivo antioxidant effects of green and black tea in man" Eur J Clin Nutr 50(1), 28-32 (1996 Jan).
Ji, B.T. et al. "Green tea consumption and the risk of pancreatic and colorectal cancers" Intl J Cancer 70(3), 255-258 (1997 Jan 27).
Murray, Michael T. The Healing Power of Herbs. Prima Publishing, 1995.
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