Green Tea Extract
Camellia sinensis. Family: Theaceae
black tea, Chinese tea, Oolong tea, tea
Green tea is obtained from the plant Camellia sinensis. Black tea, green tea, and Oolong tea are all produced from varieties of the same plant. The different types of tea are created using different processing methods.
Green tea extract contains a variety of polyphenols that includes the most active polyphenol, epigallocatechin gallate. Green tea and Oolong tea have the highest levels of polyphenols, giving them the greatest health benefits. The fermentation and processing involved in creating black tea decreases the polyphenols by converting them to theaflavins and thearubigins. All of the teas contain catechins and tannins in varying amounts.
Other significant constituents include caffeine, theobromine, and theophylline. The polyphenols of green tea are strong antioxidants that help protect against development of vascular plaque, lower cholesterol, and inhibit growth of diarrhea-causing bacteria. Green tea constituents act on the immune system to potentially help block the formation of cancer-causing compounds and suppress cancer-causing agents.
Tea is the second most popular beverage in the world and is consumed for its flavor and stimulant effect.
Current evidence suggests that the polyphenols contained in tea, particularly green tea, may help reduce the risk of certain types of cancers including oral, esophageal, and stomach cancers in humans. Protection against colon, lung, and skin cancer has been shown in animals. The polyphenols include the following catechins: (Catechins are also well recognized as antioxidants and, as such, may decrease the risk of developing atherosclerosis by preventing the oxidation of low density lipoproteins [LDL].)
Of these, epigallocatechin gallate is the largest fraction (40 percent of the polyphenol) and is believed to be the most active. The preventive activities of EGCG are described as anticarcinogenic (preventing cancer promotion), anti-mutagenic (not causing genetic mutations), and anti-reactive (blocking interaction of tumor promoters with their receptors).
The theophylline (and to a lesser extent, theobromine) in tea act as a bronchodilator. Tea has classically been used to treat mild asthma and bronchitis. Although other potent anti-asthma medications are available with more therapeutic benefit, tea may be beneficial for mild respiratory problems and is safe, even for children.
Tea is used as a stimulant drink. The methylxanthines, specifically caffeine, increase alertness and produce mild stimulation.
Green tea has an anti-microbial effect against the bacteria that cause diarrhea, and therefore may help in treating simple diarrhea. Green tea also inhibits oral bacteria. Along with fluoride, tea may help prevent tooth decay.
Please note that this section reports on claims that have NOT yet been substantiated through scientific studies.
Green tea is claimed to be an astringent (useful in stopping hemorrhages), mild diuretic, and effective in lowering cholesterol.
Dosage is measured according to the volume of polyphenols. A common daily dose of green tea is 250 to 350 milligrams of polyphenols twice a day. One cup of brewed tea contains approximately 80 to 100 milligrams of polyphenols.
Different extract strengths are available in capsules. If the product is standardized at 95 percent polyphenols, each capsule will contain about 260 to 360mg of tea extract and should be taken twice a day. If the product is standardized at 50 percent polyphenols, two capsules weighing 375 mg to 525 mg each of tea extract should be taken twice a day. (The powdered extract in capsules is sometimes standardized for epigallocatechin gallate content, and sometimes for total polyphenol content.)
Green tea infused from loose, dried leaves or from tea bags should be steeped in hot, but not scalding, water for a short period of time to preserve the important chemical substances present in the leaf.
As with any caffeine-containing product, green tea can cause anxiety, tremors, irritability, and sleeping problems if taken in excessive doses or by individuals sensitive to caffeine. Side effects are less common with green tea than with other caffeine-containing beverages because the leaves are steeped for a relatively shorter time.
Although the fluoride content of green tea may help prevent tooth decay, tea also contains tannic acid, which can stain teeth.
Tea is used worldwide with no harmful effects, however, as a general rule women who are pregnant or breast-feeding should consult a physician before taking any herbal medicines.
There are no known significant food or drug interactions. However, since green tea acts as a mild stimulant, it is best to avoid using it with other stimulants.
Generally recognized as safe (GRAS). The American Pharmaceutical Association gives Camellia sinensis a rating of 3. A 3 rating indicates that studies on the effectiveness and safety of this substance are conflicting, or there are not enough studies to draw a conclusion.
Approved as an over-the-counter drug.
Japanese Pharmacopoeia (a compendium of drugs recognized by the government).
General sales list (GSL).
Click here for a list of reputable Web sites with general information on nutrition.
Gruenwald J, Brendler T, Jaenicke C, eds. PDR for Herbal Medicines. Montvale, NJ: Medical Economics Company; 1998.
Blumenthal M, Gruenwald J, Hall T, Rister RS, eds. German Commission E Monographs. Austin, TX: American Botanical Council; 1997.
The US Department of Agriculture publications
Peirce A. The American Pharmaceutical Association: Practical Guide to Natural Medicines. New York, NY: Stonesong Press; 1999.
Murray MT. The Healing Power of Herbs: The Enlightened Persons Guide to the Wonders of Medicinal Plants. 2nd ed. Rocklin, CA: Prima Publishing; 1995.
Rosen S, et al. Anticariogenic effects of tea in rats. Journal of Dental Research. 1984;63(5):658-60.
Achiwa Y, Hibasami H, Katsuzaki H, Imai K, Komiya T. Inhibitory effects of persimmon (Diospyros kaki) extract and related polyphenol compounds on growth of human lymphoid leukemia cells. Biosci Biotechnol Biochem. 1997;61(7):1099-101.
Dong Z, Ma W, Huang C, Yang CS. Inhibition of tumor promoter-induced activator protein 1 activation and cell transformation by tea polyphenols, (-)-epigallocatechin gallate, and theaflavins. Cancer Res. 1997;57(19):4414-9.
Weisburger JH, Rivenson A, Aliaga C, et al. Effect of tea extracts, polyphenols, and epigallocatechin gallate on azoxymethane-induced colon cancer. Proc Soc Exp Biol Med. 1998;217(1):104-8.
Hollman PC, Katan MB. Absorption, metabolism and health effects of dietary flavonoids in man. Biomed Pharmacother. 1997;51(8):305-10.
Hibasami H, Komiya T, Achiwa Y, et al. Induction of apoptosis in human stomach cancer cells by green tea catechins. Oncol Rep. 1998;5(2):527-9.
Aucamp J, Gaspar A, Hara Y, Apostolides Z. Inhibition of xanthine oxidase by catechins from tea (Camellia sinensis). Anticancer Res. 1997;17(6D):4381-5.
Tanaka K, Hayatsu T, Negishi T, Hayatsu H. Inhibition of N-nitrosation of secondary amines in vitro by tea extracts and catechins. Mutat Res. 1998;412(1):91-8.
Khafif A, Schantz SP, Chou TC, Edelstein D, Sacks PG. Quantitation of chemopreventive synergism between (-)-epigallocatechin-3-gallate and curcumin in normal, premalignant and malignant human oral epithelial cells. Carcinogenesis. 1998;19(3):419-24.
Weisburger JH. Second international scientific symposium on tea and human health: an introduction. Proc Soc Exp Biol Med. 1999;220(4):193-4.
Ringer DP. Comments on the importance of diet and nutrition in cancer prevention and the role of the 2nd international science symposium on tea and human health. Proc Soc Exp Biol Med. 1999;220(4):195-6.
Fujiki H. Two stages of cancer prevention with green tea. J Cancer Res Clin Oncol. 1999;125(11):589-597.
Ahmad N, Mukhtar H. Green tea polyphenols and cancer: biologic mechanisms and practical implications. Nutr Rev. 1999;57(3):78-83.
Muto S, Yokoi T, Gondo Y, et al. Inhibition of benzo[a]pyrene-induced mutagenesis by (-)- epigallocatechin gallate in the lung of rpsL transgenic mice. Carcinogenesis. 1999;20(3):421-4.
van het Hof KH, Wiseman SA, Yang CS, Tijburg LB. Plasma and lipoprotein levels of tea catechins following repeated tea consumption. Proc Soc Exp Biol Med. 1999;220(4):203-9.
Steele VE, Bagheri D, Balentine DA, et al. Preclinical efficacy studies of green and black tea extracts. Proc Soc Exp Biol Med. 1999;220(4):210-2.
Yang CS, Kim S, Yang GY, et al. Inhibition of carcinogenesis by tea: bioavailability of tea polyphenols and mechanisms of actions. Proc Soc Exp Biol Med. 1999;220(4):213-7.
Li N, Sun Z, Han C, Chen J. The chemopreventive effects of tea on human oral precancerous mucosa lesions. Proc Soc Exp Biol Med. 1999;220(4):218-24.
Fujiki H, Suganuma M, Okabe S, et al. Mechanistic findings of green tea as cancer preventive for humans. Proc Soc Exp Biol Med. 1999;220(4):225-8.
Conney AH, Lu Y, Lou Y, Xie J, Huang M. Inhibitory effect of green and black tea on tumor growth. Proc Soc Exp Biol Med. 1999;220(4):229-33.
Mukhtar H, Ahmad N. Mechanism of cancer chemopreventive activity of green Tea. Proc Soc Exp Biol Med. 1999;220(4):234-8.
Dashwood RH, Xu M, Hernaez JF, Hasaniya N, Youn K, Razzuk A. Cancer chemopreventive mechanisms of tea against heterocyclic amine mutagens from cooked meat. Proc Soc Exp Biol Med. 1999;220(4):239-43.
Klaunig JE, Xu Y, Han C, et al. The effect of tea consumption on oxidative stress in smokers and nonsmokers. Proc Soc Exp Biol Med. 1999;220(4):249-54.
Weisburger JH. Tea and health: the underlying mechanisms. Proc Soc Exp Biol Med. 1999;220(4):271-5.
Chan PT, Fong WP, Cheung YL, Huang Y, Ho WK, Chen ZY. Jasmine green tea epicatechins are hypolipidemic in hamsters (Mesocricetus auratus) fed a high fat diet. J Nutr. 1999;129(6):1094-101.
Benzie IF, Szeto YT, Strain JJ, Tomlinson B. Consumption of green tea causes rapid increase in plasma antioxidant power in humans [In Process Citation]. Nutr Cancer. 1999;34(1):83-7.
Lin JK, Liang YC, Lin-Shiau SY. Cancer chemoprevention by tea polyphenols through mitotic signal transduction blockade. Biochem Pharmacol. 1999;58(6):911-5.