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 and National Institutes of Health (NIH): Green Tea .)
Претензії
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.
Докази
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. 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). Most studies have had methodological limitations, and the majority of studies primarily are carried out in populations that limit generalizability to other populations. 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.
Побічні ефекти
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). However, the United States Pharmacopeia (USP) review of green tea hepatotoxicity has reported that the fasting state greatly increases catechin bioavailability, possibly by saturating hepatic first-pass elimination (9). Because there may be hepatocellular patterns of liver injury, products that have USP verification stamps are labeled to state that brewed green tea should not be taken on an empty stomach and to consult with a healthcare provider if symptoms of liver problems develop. The risk of liver injury from drinking brewed green tea on an empty stomach has not been adequately studied.
Взаємодія лікарських засобів
Vitamin K in green tea may antagonize the anticoagulant effect of warfarin.
If green tea consumption is abruptly stopped, lithium serum concentrations may increase and lithium adverse effects may occur.
Green tea may decrease blood levels of nadolol, a beta blocker, as well as the antihyperlipidemic drugs atorvastatin and rosuvastatin.
Green tea may also decrease absorption of iron and folic acid.
(See also table Some Possible Dietary Supplement–Drug Interactions.)
Джерела літератури
1. 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
2. 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
3. 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
4. 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
5. 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
6. 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
7. 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
8. 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
9. Oketch-Rabah HA, Roe AL, Rider CV, et al: United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts. Toxicol Rep 7:386-402, 2020. doi:10.1016/j.toxrep.2020.02.008
Додаткова інформація
The following English-language resource 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
