Time for tea Health Article

A growing number of studies suggest that drinking tea, especially green tea, is good for you.

Tea drinking has been associated with health benefits for centuries, but only in recent years have its medicinal properties been investigated scientifically. Tea’s health benefits are thought to be largely due to its high content of flavonoids — plant-derived compounds that are antioxidants. Antioxidants neutralize the activities of unstable molecules known as free radicals, which are natural metabolic products that can damage DNA and other cell components.

Tea, particularly green tea, is the best food source of a group of flavonoids called catechins (pronounced CAT-ih-kins). In test tubes, catechins are more powerful than vitamins C and E in halting oxidative damage to cells and appear to have other disease-fighting properties. Tea contains more than 4,000 compounds, so many more may affect the body.

Types of tea

All three conventional teas — green, black, and oolong — come from the same plant (Camellia sinensis), but their chemical content and flavors are different because they’re processed differently. Green tea leaves are steamed before they’re dried, which prevents the breakdown of catechins and preserves their green color. Black tea is made by allowing the leaves to oxidize and ferment, which darkens them and converts some of the catechins into other compounds. Oolong tea is only partially fermented.

Going green against cancer

Although studies of tea use in humans have had somewhat mixed results, many have found an association between consuming green tea and a reduced risk for several cancers, including skin, breast, lung, colon, esophageal, and bladder cancers. Laboratory and animal research offers some clues about tea’s cancer-fighting potential.

One of the catechins found most abundantly in green tea is epigallocatechin-3-gallate (EGCG). In addition to being an antioxidant, EGCG may interfere with the production of an enzyme required for cancer cell growth. In laboratory cultures, EGCG has been shown to kill leukemia cells, inhibit the overgrowth of cervical cells, rescue dying skin cells, and promote apoptosis, the built-in program for cell death needed to keep cell growth in check. EGCG may also block angiogenesis, the development of blood vessels that supply cancer cells. In one study, applying green tea extracts containing EGCG to the skin helped protect it from ultraviolet light damage. Green tea also inhibits the formation of cancer-causing compounds called nitrosamines in both animals and humans.

Clinical trials are needed to determine the effectiveness of green tea and compounds such as EGCG in fighting cancer. Several are under way, including a test of green tea extract against bladder cancer recurrence in former smokers.

More health benefits

Some epidemiological studies have found a reduced risk for heart disease in regular consumers of green and black teas. Several mechanisms may be at work. The antioxidants in green, black, and oolong teas can help block the oxidation of LDL (bad) cholesterol, which can lead to plaque formation on artery walls. Drinking tea has also been shown to increase HDL (good) cholesterol in a dose-dependent way, and to improve artery function. Research results published this year indicated that green tea and black tea were equally effective in improving cholesterol levels and preventing atherosclerosis in an animal model.

A Chinese study published recently in the Archives of Internal Medicine showed a 46%–65% reduction in hypertension risk in regular consumers of oolong or green tea, compared to non-consumers of tea.

Is tea for you?

Drinking a cup of tea a few times a day may be a pleasant way to get antioxidants and other healthful plant compounds. In green tea–drinking cultures, the usual amount is three cups per day. Three to five minutes of steeping is enough to bring out the catechins.

Tea is generally safe, with a few caveats. In large amounts, it can interfere with blood clotting and thus may interact with warfarin (Coumadin) and other blood thinners. Tea can also impede the absorption of iron from fruits and vegetables. Adding lemon or milk to your tea or drinking it between meals will counteract this problem. Tea also contains caffeine, albeit in smaller amounts than coffee.

The best way to get the catechins and other flavonoids in tea is to drink it freshly brewed. Decaffeinated, bottled ready-to-drink (regular and diet) tea preparations, and instant teas have less of these compounds.