Vitamin C and E intake and risk of bladder cancer: a meta-analysis of observational studies

Epidemiologic studies that investigate whether vitamin C and E intake protects against bladder cancer have yielded inconsistent results. We conducted a systematic review and meta-analysis of published cohort and case-control studies to summarize the epidemiologic evidence investigating vitamin C and E intake and bladder cancer. Studies were identified through a search of PubMed and Embase databases and of references from relevant publications. Meta-analyses were conducted to estimate summary risk estimates (REs) and 95% confidence intervals (CIs) for vitamin C and E intake using fixed- or random-effects model depending on the heterogeneity of the studies. Subgroup analyses were performed according to study design, sex, geographical regions and source of vitamins intake. The summary REs of bladder cancer for all published studies was 0.90 (95% CI, 0.79-1.00) and 0.82 (95% CI, 0.72-0.90) for vitamin C and E intake, respectively, with no evidence of between-study heterogeneity for vitamin E, but some heterogeneity for vitamin C intake. Although some of the summary effects were non-significant, subgroup analyses showed that these inverse relationships were not modified by study design, sex, geographical regions and source of vitamins intake for vitamin E intake. Our results indicated that high intake of vitamin E could reduce bladder cancer risk. However, the inverse association between vitamin C and bladder cancer seemed to be limited. Further studies using larger samples and a rigorous methodology are warranted.