The Continuing Debate Over Green Tea

Medically Reviewed by Gary D. Vogin, MD

Feb. 28, 2001 -- Green tea is good for you, right? Thanks to chemicals called polyphenols, which have an antioxidant effect that protects against infection, heart disease, and even cancer, it may very well be. But a large Japanese study in the March 1 issue of TheNew England Journal of Medicine did not show any protective effect of green tea against stomach cancer.

"There is a strong belief that green tea provides protection against cancer," researcher Yoshitaka Tsubono, MD, tells WebMD. "It is a good idea to drink green tea for pleasure, but probably not so at present for aiming at the prevention of [stomach] cancer." Tsubono is a lecturer in epidemiology, public health, and forensic medicine at the Tohoku University Graduate School of Medicine in Japan.

This study is the largest so far to collect information about green tea consumption and other health habits while tracking which individuals develop stomach cancer. It was done in Miyagi Prefecture in northern Japan, where people have relatively high rates of stomach cancer. From 1984 through 1992, more than 26,000 individuals were followed, and 419 of them developed stomach cancer.

Green tea consumption was not associated with risk of stomach cancer, once adjustments were made for other factors that could affect risk, including sex, age, history of stomach ulcer, use of tobacco or alcohol, and other dietary habits.

"From the results of this study, green tea does not appear to prevent stomach cancer in a high-risk group," Iris F. Benzie, MD, tells WebMD. "The World Cancer Research Fund also concluded that neither tea nor coffee is associated with an increase or a decrease in risk of [stomach] cancer.

"Whether tea can slow the development of [stomach] cancer, and its possible protective effects ... remain to be established," says Benzie, an associate professor of biomedical science at the Hong Kong Polytechnic University in Kowloon, China.

As consumption of green tea reduced cancer risk in many laboratory studies, additional studies are needed to clarify the effect of green tea in human cancer, explains Hasan Mukhtar, PhD, a professor and research director of dermatology at Case Western Reserve University in Cleveland.

"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.