Green tea consumption and gastric cancer in Japanese: A pooled analysis of six cohort studies

Manami Inoue ^1*, Shizuka Sasazuki ¹, Kenji Wakai ², Takeshi Suzuki ³, Keitaro Matsuo ³, Taichi Shimazu ¹, Ichiro Tsuji ⁴, Keitaro Tanaka ⁵, Tetsuya Mizoue ⁶, Chisato Nagata ⁷, Akiko Tamakoshi ⁸, Norie Sawada ¹ and Shoichiro Tsugane ¹

¹ Research Center for Cancer Prevention and Screening, National Cancer Center, Japan
² Nagoya University Graduate School of Medicine, Japan
³ Aichi Cancer Center Research Institute, Japan
⁴ Tohoku University Graduate School of Medicine, Japan
⁵ Faculty of Medicine, Saga University, Japan
⁶ Research Institute, International Medical Center of Japan, Japan
⁷ Gifu University Graduate School of Medicine, Japan
⁸ Aichi Medical University School of Medicine, Japan

^* To whom correspondence should be addressed. E-mail: mnminoue{at}ncc.go.jp.

Accepted 16 May 2009

Abstract

Background: 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.

Objective: To examine the association between green tea consumption and gastric cancer.

Methods: We analyzed original data from six cohort studies that measured green tea consumption using validated questionnaires at baseline. Hazard ratios (HR) in the individual studies were calculated, with adjustment for a common set of variables, and combined using a random-effects model.

Results: During 2,285,968 person-years of follow-up of a total of 219,080 subjects, 3,577 gastric cancer cases were identified. Compared with those drinking <1 cup/day, no significant risk reduction for gastric cancer was observed with increased green tea consumption in men, even in stratified analyses by smoking status and subsite. In women, however, a significantly decreased risk was observed for those with consumption of 5 cups/day (multivariate-adjusted pooled HR =0.79, 95% confidence interval (CI) =0.65-0.96). This decrease was also significant for the distal subsite (HR=0.70, 95%CI=0.50-0.96). In contrast, a lack of association for proximal gastric cancer was consistently seen in both men and women.