Coffee consumption and bladder cancer in nonsmokers: a pooled analysis of case-control studies in European countries

Background: Coffee consumption has been associated with an excess bladder c ancer risk, but results from epidemiological studies are inconsistent. This association has been long debated, in part due to the potential confoundin g by smoking. We examined the risk associated with coffee consumption in no nsmokers in a pooled analysis of ten European bladder cancer case-control s tudies. Methods: The pooled data set comprises 564 cases and 2929 hospital or popul ation controls who had never smoked. They were enrolled in ten studies cond ucted in Denmark, Germany, Greece, France, Italy and Spain. Information on coffee consumption and occupation was re-coded following standard criteria. Unconditional logistic regression was applied adjusting for age, study cen ter, occupation and gender. Results: Seventy-nine percent of the study population reported having drunk coffee, and 2.4% were heavy drinkers, reporting having drunk on average te n or more cups per day. There was no excess risk in ever coffee drinkers (O R = 1.0, 95% CI 0.8-1.3) compared to never drinkers. The risk did not incre ase monotonically with dose but a statistically significant excess risk was seen for subjects having drunk ten or more cups per day (OR = 1.8, 95% CI 1.0-3.3). This excess was seen in both men and women. There was no evidence of an association of the risk with duration or type of coffee consumption. The pooled results were not dependent on the findings of any specific stud y, but they depended on the type of controls with an overall excess risk ob served only for studies using hospital controls. Conclusion: Nonsmokers who are heavy coffee drinkers may have a small exces s risk of bladder cancer. Although these results cannot be attributed to co nfounding by smoking, the possibility of bias in control selection cannot b e discarded. On the basis of these results, only a very small proportion of cancers of the bladder among nonsmokers could be attributed to coffee drin king.