Fruits, vegetables, and bladder cancer risk: a systematic review and meta-analysis

Smoking is estimated to cause about half of all bladder cancer cases. Case-control studies have provided evidence of an inverse association between fruit and vegetable intake and bladder cancer risk. As part of the World Cancer Research/American Institute for Cancer Research Continuous Update Project, we conducted a systematic review and meta-analysis of prospective studies to assess the dose-response relationship between fruit and vegetables and incidence and mortality of bladder cancer. We searched PubMed up to December 2013 for relevant prospective studies. We conducted highest compared with lowest meta-analyses and dose-response meta-analyses using random effects models to estimate summary relative risks (RRs) and 95% confidence intervals (CIs), and used restricted cubic splines to examine possible nonlinear associations. Fifteen prospective studies were included in the review. The summary RR for an increase of 1 serving/day (80 g) were 0.97 (95% CI: 0.95-0.99) I(2)  = 0%, eight studies for fruits and vegetables, 0.97 (95% CI: 0.94-1.00, I(2)  = 10%, 10 studies) for vegetables and 0.98 (95% CI: 0.96-1.00, I(2)  = 0%, 12 studies) for fruits. Results were similar in men and women and in current, former and nonsmokers. Amongst fruits and vegetables subgroups, for citrus fruits the summary RR for the highest compared with the lowest intake was 0.87 (95% CI: 0.76-0.99, I(2)  = 0%, eight studies) and for cruciferous vegetables there was evidence of a nonlinear relationship (P = 0.001). The current evidence from cohort studies is not consistent with a role for fruits and vegetables in preventing bladder cancer.