Green tea drinkers show lower cancer risks

Older women who regularly drink green tea may have slightly lower risks of colon, stomach and throat cancers than women who make no time for tea, a large study suggests.

Researchers found that of more than 69,000 Chinese women followed for a decade, those who drank green tea at least three times a week were 14 percent less likely to develop a cancer of the digestive system. That mainly meant lower odds of colon, stomach and esophageal cancers. No one can say whether green tea, itself, is the reason. Green-tea lovers are often more health-conscious in general.

The study did try to account for that, said senior researcher Dr. Wei Zheng, who heads epidemiology at Vanderbilt University School of Medicine in Nashville. None of the women smoked or drank alcohol regularly. And the researchers collected information on their diets, exercise habits, weight and medical history. Even with those things factored in, women's tea habits remained linked to their cancer risks, Zheng noted.

Still, he said in an email, this type of study cannot prove cause-and-effect. What's more, past studies have so far come to conflicting findings on whether green-tea drinkers really do have lower cancer risks. All of those studies are hampered by the fact that it's hard to isolate the effect of a single food in a person's diet on the risk of cancer. Really, the only types of studies that can give strong evidence of cause-and-effect are clinical trials, wherein people would be randomly assigned to use green tea in some form, or not.

But few clinical trials have looked at whether green tea can cut cancer risk, and their results have been inconsistent, according to the National Cancer Institute. There is "strong evidence" from lab research - in animals and in human cells - that green tea has the potential to fight cancer, Zheng's team writes in the American Journal of Clinical Nutrition.

Green tea contains certain antioxidant chemicals - particularly a compound known as EGCG - that may ward off the body-cell damage that can lead to cancer and other diseases. For their study, Zheng and his colleagues used data from a long-running health study of over 69,000 middle-aged and older Chinese women. More than 19,000 were considered regular green-tea drinkers. (They had the beverage at least three times per week.)

Over 11 years, 1,255 women developed a cancer of the digestive system. In general, the risks were somewhat lower when a woman drank green tea often and for a long time. For example, women who said they'd regularly had green tea for at least 20 years were 27 percent less likely than non-drinkers to develop any digestive system cancer. And they were 29 percent less likely to develop colorectal cancer, specifically.

None of that proves you should start drinking green tea to thwart cancer.

Women who downed a lot of green tea in this study were also younger, ate more fruits and vegetables, exercised more and had higher-income jobs. The researchers adjusted their data for all those differences - but, they write, it's not possible to perfectly account for everything. If you want to start drinking green tea, it's considered safe in moderate amounts, says the National Center for Complementary and Alternative Medicine. But the tea and its extracts do contain caffeine, which some people may need to avoid.

Green tea also contains small amounts of vitamin K, which means it could interfere with drugs that prevent blood clotting, like warfarin. Since many older people are on multiple medications, it's wise for them to talk with their doctors before using green tea as a health tonic. This will be published in American Journal of Clinical Nutrition, November, 2012. http://bit.ly/OZXHcT 

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