Vitamin D and Bladder Cancer Risk: An Umbrella Review and Second Order Meta‐Analysis

Low serum vitamin D is consistently associated with increased bladder cancer risk, while maintaining levels above 30 nmol/L may provide some protection. Evidence on dietary intake and supplementation remains inconclusive. Future studies should adopt standardized methods for vitamin D measurement, explore the role of free versus total vitamin D, and clarify population-specific differences to better define vitamin D's role in bladder cancer prevention.