Background: Although laboratory experiments suggest protective effects of green tea against colorectal cancer, few prospective cohort studies have been conducted.
Methods: We conducted a pooled analysis of two prospective cohort studies among residents in Miyagi Prefecture in rural northern Japan. The first study started in 1984 and included 26,311 subjects. The second study started in 1990 and included 39,604 subjects. The subjects responded to a self-administered questionnaire including an item on green tea consumption. With 7 to 9 years of follow-up, 305 colon and 211 rectal cancers were identified in the two cohorts through record linkage to a regional cancer registry. We used Cox regression to estimate the hazard ratio (HR) of colorectal cancer according to the consumption of green tea with adjustment for potential confounders, and pooled the estimates obtained from each cohort by general variance-based method.
Results: Multivariate pooled HRs for colon cancer associated with drinking 1-2, 3-4, and 5 or more cups of green tea per day, as compared with less than 1 cup per day, were 1.06 (95% confidence interval [CI]=0.74-1.52), 1.10 (0.78-1.55), 0.97 (0.70-1.35), respectively (trend p=0.81). Corresponding HRs for rectal cancer were 0.85 (95% CI=0.56-1.29), 0.70 (0.45-1.08), 0.85 (0.58-1.23), respectively (trend p=0.31).
Conclusions: Consumption of green tea was not associated with lower risk of colorectal cancer.