Meta-analysis of longitudinal studies: Serum vitamin D and prostate cancer risk

Aim: To review and summarize evidence from longitudinal studies on the association between serum 25-hydroxyvitamin D (25(OH)D) and the risk of prostate cancer (PC). Methods: Relevant prospective cohort studies and nested case-control studies published until July 2009 were identified by systematically searching Ovid Medline, EMBASE, and ISI Web of Knowledge databases and by cross-referencing. The following data were extracted in a standardized manner from eligible studies: first author, publication year, country, study design, characteristics of the study population, duration of follow-up, PC incidence/PC mortality according to serum vitamin D status and the respective risk ratios, and covariates adjusted for in the analysis. Due to the heterogeneity of studies in categorizing serum vitamin D levels, all results were recalculated for an increase in serum 25(OH)D by 10 ng/ml. Summary odds ratios (ORs) were calculated using meta-analysis methods. Results: Overall, eleven original articles were included, ten of which reported on the association between serum vitamin D levels and PC incidence and one article reported on the association with PC mortality. Meta-analysis of studies on PC incidence resulted in a summary OR (95% confidence interval, CI) of 1.03 (0.96–1.11) associated with an increase of 25(OH)D by 10 ng/ml (P = 0.362). No indication for heterogeneity and publication bias was found. Conclusions: According to available evidence from longitudinal studies, serum 25(OH)D is not associated with PC incidence.