"The outcome of this study differs from many other studies in which risk of stomach cancer goes down as green tea consumption goes up," Mukhtar tells WebMD after reviewing the study. "Like many nutritional epidemiological studies, this study also has merits and limitations."
Edzard Ernst, MD, a professor of complementary medicine at the University of Exeter in Devon, England, agrees that the study is "burdened with several weaknesses," and calls the findings "interesting but not compelling. What is needed are controlled clinical trials, but unfortunately, these would be prohibitively expensive."
Should we give up drinking green tea? Probably not, as other possible health benefits attributed to green tea were not tested by this study.
In an editorial accompanying the journal article, Takeshi Sano, MD, and Mitsuru Sasako, MD, from the National Cancer Center Hospital in Tokyo, note that this study did not determine whether drinking 10 cups or more daily had a protective effect. Earlier studies suggested that drinking this much green tea -- about a quart -- did protect against stomach cancer.
Another explanation for the lack of protective effect of green tea in the Japanese study might be conflicting effects of other dietary and personal habits. Individuals who drank the most green tea also ate the most pickled vegetables and smoked the most, which may increase risk of stomach cancer. On the other hand, those who drank the most green tea also ate the most fruit, which protects against stomach cancer.
"The main factor increasing risk of stomach cancer is salted, pickled foods," John H. Weisburger, MD, PhD, tells WebMD.
Fruits, vegetables, and green or black tea are all rich sources of antioxidants, which inhibit cancer cell growth and may have beneficial effects on cell breakdown seen with aging, explains Weisburger, director emeritus of the American Health Foundation in Valhalla, N.Y.
"For good health, I recommend five to 10 servings of fruits and veggies and five to 10 cups of tea daily," he says.