Green tea is made from the dried leaves of the same plant as traditional tea. However, traditional tea leaves are fermented, andgreen tea leaves are steamed but unfermented. Green tea may be brewed and drunk or ingested in tablet or capsule form. Green teacontains caffeine, but many extracts have been decaffeinated. It is high in flavonoids, polyphenols, and catechins. Those substances areantioxidants, often thought to protect cells from damage by oxygen, mutations, and cancer.
(See also Overview of Dietary Supplements.)
Claims for Green Tea
People take green tea for many reasons, including prevention of cancer and coronary artery disease, as well as treatment of external genital warts. Other reasons are reduction of fat (lipid) levels in the blood, relief of osteoarthritis pain and menopausal symptoms, and enhancement of weight loss, memory, and longevity.
Evidence for Green Tea
Few of the benefits claimed for green tea are supported by strong scientific evidence. However, topical green tea (applied directly on the wart) may help treat genital warts. Studies have also shown a small but significant loss of weight among users.
Side Effects of Green Tea
Side effects are related to the effects (including the dose) of caffeine. They include insomnia, anxiety, rapid heart rate (tachycardia), and mild tremor. Pregnant women should avoid excessive amounts due to the caffeinecontent, because of the risk of miscarriage. Rare case reports document liver toxicity. Drinking brewed green tea on an empty stomach may increase the risk of liver injury, although this has not been adequately studied.
Drug Interactions with Green Tea
Vitamin K in green teamay decrease anticoagulant effects of warfarin, thus increasing the risk of blood clots.
Green teamay decrease blood levels of nadolol, a beta-blocker, as well as medications that help lower cholesterol levels (atorvastatin and rosuvastatin).
If green tea consumption is abruptly stopped, lithium blood levels may increase andlithium adverse effects may occur.
Green teamay also decrease absorption of iron and folic acid.
Recommendations for Green Tea
Green teais generally considered safe, although the health benefits, if any, are likely small. People should avoid drinking large amounts, especially if pregnant, and should avoid drinking green tea on an empty stomach.
More Information
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's National Center for Complementary and Integrative Health: Green Tea
