The association between coffee consumption and bladder cancer incidence in a pooled analysis of the Miyagi Cohort Study and Ohsaki Cohort Study.

Recent epidemiological studies of the association between coffee consumption and the risk of bladder cancer have yielded conflicting results. The aim of the present study was to examine the association between coffee consumption and the incidence of bladder cancer on the basis of pooled data from two cohort studies carried out in Miyagi Prefecture, northeastern Japan. We delivered self-administered questionnaires inquiring about the frequency of coffee consumption and other lifestyle factors in 1990 for the Miyagi Cohort Study and in 1994 for the Ohsaki Cohort Study. We followed 73 346 individuals from both cohorts and identified 274 cases of bladder cancer during 17.6 years for the Miyagi Cohort Study and 13.3 years for the Ohsaki Cohort Study. The multivariate-adjusted hazard ratios (95% confidence intervals) of bladder cancer incidence for the individuals who drank coffee occasionally, 1-2 cups/day, and 3 or more cups/day compared with never drinkers were 1.22 (0.90-1.66), 0.88 (0.61-1.26), and 0.56 (0.32-0.99), respectively (Ptrend=0.04). The inverse association remained even after stratification for smoking status. These data indicate that there is a significant inverse association between coffee consumption and the risk of bladder cancer.