June 22, 2009 — Green tea drinking is associated with lower risk for distal gastric cancer in women but not in men, according to the results of a meta-analysis of original data from 6 cohort studies reported in the June 7 Online First issue of Gut.
"Previous experimental studies have suggested many possible anti-cancer mechanisms for green tea, but epidemiologic evidence for the effect of green tea consumption on gastric cancer risk is conflicting," write Manami Inoue, MD, PhD, from the National Cancer Center in Tokyo, Japan, and colleagues from the Research Group for the Development and Evaluation of Cancer Prevention Strategies in Japan. "We conducted a pooled analysis of several large-scale population-based cohort studies in Japan on the association between green tea consumption and gastric cancer risk."
The investigators calculated adjusted hazard ratios (HRs) from original data in 6 individual cohort studies that measured baseline green tea consumption in 219,080 subjects using validated questionnaires. HRs were combined with use of a random-effects model.
There were 3577 cases of gastric cancer detected during 2,285,968 person-years of follow-up. Increased green tea consumption in men vs those drinking less than 1 cup per day was not associated with any significant risk reduction for gastric cancer, even in analyses stratified by smoking status and subsite.
In women drinking 5 or more cups per day, however, there was a significantly decreased risk for gastric cancer, both overall (multivariate-adjusted pooled HR, 0.79; 95% confidence interval [CI], 0.65 - 0.96) and at the distal subsite (HR, 0.70; 95% CI, 0.50 - 0.96). For both men and women, there was no association between green tea consumption and the risk for proximal gastric cancer.
"Green tea may decrease the risk of distal gastric cancer in women," the study authors write. "Further investigation of our findings of differences in effect by sex and subsite will help elucidate the mechanism underlying the etiology of gastric cancer."
Limitations of this study include collection of data on green tea consumption only at baseline, possible residual confounding, and rarity of nondrinkers of green tea in Japan. In addition, some data were missing on Helicobacter pylori infection status, and some subjects with gastric cancer may have decreased their tea drinking before the diagnosis because of their symptoms.
A grant for the Third Term Comprehensive Control Research for Cancer from the Ministry of Health, Labour and Welfare of Japan supported this study. The study authors have disclosed no relevant financial relationships.
Gut. Published online June 7, 2009.
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