Green tea is made from the dried leaves of the same plant (Camellia sinensis) as traditional tea, an evergreen shrub native to Asia. However, traditional tea leaves are fermented, and green tea leaves are steamed but unfermented. Green tea may be brewed and drunk or ingested in extracted tablet or capsule form. It has multiple components that are thought to have antioxidant and anticancer effects. Green tea contains polyphenols and catechins as well as caffeine, but green tea is known to have lower amounts of caffeine than coffee, and many extracts have been decaffeinated.
(See also Overview of Dietary Supplements.)
Green tea is said to have multiple health benefits, few of which are supported by strong scientific evidence. It has been used to treat genital warts, increase mental alertness (because of its caffeine), prevent cancer, help in weight loss, reduce serum lipids, prevent coronary artery disease, enhance memory, relieve osteoarthritis pain, treat menopausal symptoms, and contribute to longevity.
Green tea, the drink and the extract, is one of the most highly studied supplements on the market; however, the beneficial clinical evidence for the drink is limited. Recently, certain active ingredients found in green tea (sinecatechins, trade names Veregen and Polyphenon E) have been approved for the treatment of genital warts due to human papillomavirus infection. A randomized controlled study indicated that the defined extract (55% epigallocatechin gallate) is efficacious and safe for genital and perianal warts (1). A 2011 systematic review and meta-analysis of 3 studies (1247 subjects) of 10% and 15% Polyphenon E verified efficacy for treatment of external anogenital warts (2). Another study indicated that the treatment with the green tea–derived extract yielded a lower cost of treatment compared to traditional pharmaceutical treatments (3).
Numerous meta-analyses of the clinical trials available indicate that green tea is safe for moderate and regular consumption. In addition, small, most often nonsignificant, benefits are evident for weight loss (4) and cardiovascular disease prevention, while there is insufficient and often conflicting evidence for any benefit from consumption of green tea for cancer prevention (5). However, one meta-analysis correlated daily consumption of 7 cups of green tea with reduced prostate cancer (6), and a different meta-analysis reported favorable cardiovascular outcomes (7). Further, more rigorously designed large scale clinical trials are needed before claims can be confirmed. Possibly confounding evidence from population studies is that in nations in which green tea is regularly consumed, other cultural, behavioral, or genetic factors may contribute to good health.
Adverse effects are most commonly related to effects of caffeine. They include insomnia, anxiety, tachycardia, and mild tremor. Pregnant women should avoid excessive caffeine.
Rare case reports document hepatotoxicity. A 2016 review of randomized controlled trials that evaluated hepatotoxicity found adverse liver events in a few subjects in the green tea intervention groups, mostly self-limited elevations in liver enzymes (8).
Stockfleth E, Beti H, Orasan R, et al: Topical Polyphenon E in the treatment of external genital and perianal warts: a randomized controlled trial. Br J Dermatol 158(6):1329-1338, 2008. doi: 10.1111/j.1365-2133.2008.08520.x.
Tzellos TG, Sardeli C, Lallas A, et al: Efficacy, safety and tolerability of green tea catechins in the treatment of external anogenital warts: a systematic review and meta-analysis. J Eur Acad Dermatol Venereol 25(3):345-353, 2011. doi: 10.1111/j.1468-3083.2010.03796.x.
Langley PC: A cost-effectiveness analysis of sinecatechins in the treatment of external genital warts.J Med Econ 13(1):1-7, 2010. doi: 10.3111/13696990903451461.
Jurgens TM, Whelan AM, Killian L, et al: Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database Syst Rev. 12: CD008650, 2012. doi: 10.1002/14651858.CD008650.pub2.
Filippini T, Malavolti M, Borrelli F, et al: Green tea (Camellia sinensis) for the prevention of cancer. Cochrane Database Syst Rev 3(3):CD005004. doi: 10.1002/14651858.CD005004.pub3.
Guo Y, Zhi F, Chen P, et al: Green tea and the risk of prostate cancer: a systematic review and meta-analysis. Medicine (Baltimore) 96(13):e6426, 2017. doi: 10.1097/MD.0000000000006426.
Pang J, Zhang Z, Zheng TZ, et al: Green tea consumption and risk of cardiovascular and ischemic related diseases: a meta-analysis. Int J Cardiol 202:967-974, 2016. doi: 10.1016/j.ijcard.2014.12.176.
Isomura T, Suzuki S, Origasa H, et al: Liver-related safety assessment of green tea extracts in humans: a systematic review of randomized controlled trials. Eur J Clin Nutr 70(11):1221-1229, 2016. doi: 10.1038/ejcn.2016.78.
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
National Institutes of Health (NIH), National Center for Complementary and Integrative Health: General information on the use of green tea as a dietary supplement
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