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With Comments from John La Puma, MD, FACP
April 2001; Volume 4; 48
Source: Tsubono Y, et al. Green tea and the risk of gastric cancer in Japan. N Engl J Med 2001;344:632-636.
Although laboratory experiments and case-control studies have suggested that the consumption of green tea provides protection against gastric cancer, few prospective studies have been performed.
In January 1984, a total of 26,311 residents in three municipalities of Miyagi Prefecture, in northern Japan (11,902 men and 14,409 women 40 years of age or older) completed a self-administered questionnaire that included questions about the frequency of consumption of green tea. During 199,748 person-years of follow-up, through December 1992, we identified 419 cases of gastric cancer (in 296 men and 123 women). We used Cox regression to estimate the relative risk of gastric cancer according to the consumption of green tea.
Green tea consumption was not associated with the risk of gastric cancer. After adjustment for sex, age, presence or absence of a history of peptic ulcer, smoking status, alcohol consumption, other dietary elements, and type of health insurance, the relative risks associated with drinking one or two, three or four, and five or more cups of green tea per day, as compared with less than one cup per day, were 1.1 (95% confidence interval [CI], 0.8 to 1.6), 1.0 (95% CI, 0.7 to 1.4), and 1.2 (95% CI, 0.9 to 1.6), respectively (P for trend = 0.13). The results were similar after the 117 cases of gastric cancer that were diagnosed in the first three years of follow-up had been excluded, with respective relative risks of 1.2 (95% CI, 0.8 to 1.8), 1.0 (95% CI, 0.7 to 1.5), and 1.4 (95% CI, 1.0 to 1.9) (P for trend = 0.07).
In a population-based, prospective cohort study in Japan, we found no association between green tea consumption and the risk of gastric cancer.
A prospective cohort study is better evidence than a case-control study, but not as good as an intervention study. Case-control studies have suggested that the five to 10 cups of green tea are protective against the development of gastric cancer, which remains the most prevalent cancer in Japan in both men and women. Eating salty foods increases the risk of gastric cancer; eating fruits and vegetables reduces the risk.
Green tea is made by steaming fresh tea leaves at high temperature, preserving the polyphenols that appear to be antimutagenic, anticarcinogenic, and anti-inflammatory in effect. Epigallocatechin-3-gallate is the main polyphenol in green tea. To make black tea, the same leaves are oxidized and then dried; some polyphenols remain, but green tea is supposed to have a chemoprotective effect.
In this well-done study, green tea use was confounded by varying usages of other risk and protective factors—smoking (a risk factor), pickled vegetable consumption (also a risk factor), and fruit intake (a protective factor). Nevertheless, there was no evidence of protection, even at 1 liter/d consumption, which is not uncommon in Japan. The editorialists, Takeshi Sano, MD and Mitsuru Sasako, MD of the National Cancer Center Hospital in Tokyo, report that "large cohort studies and intervention trials examining the relation between green-tea consumption and gastric cancer are under way in Japan."
Drink green tea for its light color, its delicate fragrance, its history, and its warming qualities. It probably does not prevent gastric cancer by itself, but certainly has other beneficial effects.