Older women who regularly drunk green tea may have slightly lower risks of colon, stomach and throat cancers than women who don't, according to a Canadian study that followed thousands of Chinese women over a decade.
The researchers, whose report appeared in the American Journal of Clinical Nutrition, found that of the more than 69,000 women, those who drank green tea at least three times a week were 14 per cent less likely to develop a cancer of the digestive system.
The study adds to debate over the impact of green tea on cancer risks. Past studies have so far come to conflicting findings on whether green tea drinkers really do have lower cancer risks.
"In this large prospective cohort study, tea consumption was associated with reduced risk of colorectal and stomach/esophageal cancers in Chinese women," wrote study leader Wei Zheng, who heads epidemiology at Vanderbilt University school of Medicine in Nashville, and his colleagues.
Nobody can say whether green tea itself is the reason, since green tea lovers are often more health-conscious in general.
But the study did try to account for that, Zheng said. None of the women smoked or drank alcohol regularly, and the researchers also collected information on their diets, exercise habits, weight and medical history.
Yet even with all these things factored in, women's tea habits remained linked to their cancer risks, Zheng noted - even though this type of study cannot prove cause and effect.
Few clinical trials have looked at whether green tea can cut cancer risks, and the 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 wrote.
For the 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, who consumed it more than three times a week.
Over 11 years, 1,255 women developed a digestive system cancer. 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 per cent less likely than non-drinkers to develop any digestive system cancer. And they were 29 per cent less likely to develop colorectal cancer.
Green tea conctains 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.
None of this proves that people should start downing green tea to thwart cancer.
Women who downed a lot of green tea in the study were also younger, ate more fruits and vegetables, exercised more and had higher-income jobs. The researchers adjusted for those differences but, they wrote, it's impossible to perfectly account for everything.