green tea extract

Green tea extract is a concentrated supplement derived from the leaves of the Camellia sinensis plant. Unlike black tea, the leaves are steamed or pan-fried and dried rather than fermented, which preserves a group of plant antioxidants called catechins, especially epigallocatechin gallate (EGCG). The extract also contains naturally occurring caffeine and is sold as capsules, tablets, and liquids.

Despite extensive research on green tea and its extracts, authoritative reviewers say firm conclusions cannot yet be drawn for most of the purposes the products are marketed for. According to NCCIH, the catechins and caffeine in green tea may have only a modest effect on body weight, and some studies have found a small reduction in total and LDL cholesterol (with no clear effect on HDL or triglycerides). Results for cancer prevention have been inconsistent, and a link to lower heart-disease risk has been observed in Asian but not Western populations. The NIH Office of Dietary Supplements similarly characterizes any weight effect as, at most, modest. Overall the evidence is weak and should not be read as proof of benefit.

No standard or recommended dose of green tea extract has been established, and the cited authorities do not endorse a specific amount. Importantly, more is not safer: clinical trials of high-catechin products providing roughly 800 mg or more of EGCG per day have been associated with elevated liver enzymes, so high-dose extracts carry added risk. Talk with your healthcare provider before starting green tea extract, particularly about dose, any medications you take, and any history of liver problems.

Green tea consumed as a beverage is generally considered safe for most adults, but concentrated extracts carry more risk. Although uncommon, liver injury has been reported in people using green tea products, mainly extracts in tablet or capsule form; people who carry a particular immune-related gene variant (estimated at 5 to 15 percent of Americans) appear especially susceptible. Because the extract contains caffeine, people who are pregnant or breastfeeding should keep total caffeine intake within moderate limits and consult their provider. Anyone with liver concerns or taking prescription medication should seek medical advice first.

Reported side effects of green tea extract supplements include nausea, constipation, stomach discomfort, and raised blood pressure. Its caffeine content can also cause restlessness, jitteriness, or trouble sleeping. The most serious concern, though uncommon, is liver injury linked specifically to extract pills rather than to the beverage.

Green tea may interfere with certain medications. At high doses it can lower blood levels and reduce the effectiveness of the beta-blocker nadolol; it can also reduce blood levels of the cholesterol-lowering drug atorvastatin, and an interaction with the osteoporosis drug raloxifene has been documented in NCCIH-funded research. Tell your healthcare provider about all medicines and supplements you take before using green tea extract.