Tuesday, October 16, 2012. Findings from the Shanghai Women's Health Study reported online on October 10, 2012 in the American Journal of Clinical Nutrition reveal a protective effect for tea drinking against cancers of the stomach, esophagus and colon in middle-aged Chinese women.
Researchers from Vanderbilt University in Nashville, in collaboration with the Shanghai Cancer Institute, analyzed data from 69,310 nonsmoking and non-alcohol-drinking women who were between the ages of 40 and 70 years upon recruitment in 2000. Interviews and questionnaires completed upon enrollment provided information on the intake of various foods and beverages, including tea. The participants were followed for an average of 12 years, during which three follow-up surveys were conducted. Over the follow-up period, 1,255 digestive system cancers occurred, including cancers of the esophagus, colon, rectum, pancreas, stomach, gallbladder and bile duct.
Twenty eight percent of the subjects reported drinking tea regularly upon enrollment, and 88 percent of tea drinkers reported drinking green tea exclusively. Among regular tea drinkers, categorized as those who consumed tea three or more times per week over a period of no less than six months, a 17 percent lower risk of all digestive system cancers was observed in comparison with those who did not consume tea. A greater protective effect was found for participants who consumed two to three cups of tea per day, or among those who consumed tea for 20 years of more. When digestive cancers were analyzed according to type, the protective effect of tea was associated mainly with colorectal and stomach/esophageal cancers, for which there was a 27 percent lower age-adjusted risk observed among regular tea drinkers compared to non-drinkers.
Possible mechanisms for tea include the ability of its polyphenol components to scavenge free radicals, decrease tumor cell proliferation and angiogenesis, and encourage programmed cancer cell death. Protective properties including inhibition of cellular proliferation, invasion and angiogenesis, have also been attributed to tea constituents.
"We found that tea consumption was associated with reduced risk of cancers of the digestive system, particularly cancers of the stomach/esophagus and colorectum, in middle aged and older Chinese women who mainly consumed green tea," Wei Zheng and colleagues conclude. "Our results suggest that tea drinking may be a potential way to reduce risk of digestive system cancers in nonsmoking and non–alcohol-drinking women."