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Green Tea

By Melissa G. Marko, PhD, Ara DerMarderosian, PhD

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.

Claims

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.

Evidence

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). Another study indicated that the treatment with the green tea–derived extract yielded a lower cost of treatment compared to traditional pharmaceutical treatments (2).

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 seen for weight loss and cardiovascular disease prevention, while there is insufficient and often conflicting evidence for any benefit from consumption of green tea for cancer prevention (3-6). 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

Adverse effects are related to effects of caffeine. They include insomnia, anxiety, tachycardia, and mild tremor. Pregnant women should avoid excessive caffeine.

Drug interactions

Vitamin K in green tea may antagonize the anticoagulant effect of warfarin.

Green tea references

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