A dose-response meta-analysis of coffee consumption and bladder cancer.

BACKGROUND: A number of studies have examined the association between coffee consumption and risk of bladder cancer, but uncertainty about the dose-response relationship remains.

MATERIALS AND METHODS: A comprehensive search was performed to identify all observational studies providing quantitative estimates between bladder cancer risk and coffee consumption. Dose-response relationship was assessed by restricted cubic spline model and bivariate random-effect meta-regression.

RESULTS: 23 case-control studies with 7690 cases and 13,507 controls, and 5 cohort studies with 700 cases and 229,099 participants, met the inclusion criteria. Compared with non-drinkers and for case-control studies, the pooled smoking-adjusted RRs(95% CI) of bladder cancer were 1.07(1.02-1.13) for 1 cup/day, 1.15(1.05-1.26) for 2 cups/day, 1.22(1.08-1.38) for 3 cups/day, and 1.29(1.12-1.48) for 4 cups/day. For cohort studies, the pooled smoking-adjusted RRs of bladder cancer were 1.09(95% CI, 0.89-1.34) for 1 cup/day, 1.13(95% CI, 0.82-1.55) for 2 cups/day, 1.09(95% CI, 0.77-1.56) for 3 cups/day, and 1.01(95% CI, 0.69-1.48) for 4 cups/day.

CONCLUSIONS: Although data from case-control studies suggested that coffee was a risk factor for bladder cancer, there was no conclusive evidence on this association because of inconsistencies between case-control and cohort studies.