Vitamin A and risk of bladder cancer: a meta-analysis of epidemiological studies

Background: Epidemiological studies have reported the preventive effect of vitamin A intake on bladder cancer. However, the findings are inconsistent. To address this issue we conducted a meta-analysis to investigate the quantitative effects of vitamin A on bladder cancer. Methods: We searched MEDLINE and Embase databases and the references of the relevant articles in English to include studies on dietary or blood vitamin A for the risk of bladder cancer. We performed a meta-analysis using both fixed-effects and random-effects models. Results: Twenty-five articles on dietary vitamin A or blood vitamin A were included according to the eligibility criteria. The pooled risk estimates of bladder cancer were 0.82 (95% CI 0.65, 0.95) for total vitamin A intake, 0.88 (95% CI 0.73, 1.02) for retinol intake, and 0.64 (95% CI 0.38, 0.90) for blood retinol levels. We also found inverse associations between subtypes of carotenoids and bladder cancer risk. Conclusion: The findings of this meta-analysis indicate that high vitamin A intake was associated with a lower risk of bladder cancer. Larger studies with prospective design and rigorous methodology should be considered to validate the current findings.