Search strategy and inclusion criteria

PubMed and Web of Science were searched for prospective studies, examining the correlation of circulating 25[OH] D concentration with prostate cancer, which were eligible for the meta-analysis. We carried out the literature search on December 20, 2016. We used combinations of the following keywords: (“vitamin D” or “25-hydroxyvitamin D” or “25[OH]D”) AND (“prostate cancer” or “prostate carcinoma”). The references from included articles were also checked to identify any additional studies.

Only prospective cohort studies or nested case–control studies examining the associations of circulating 25[OH]D concentration with prostate cancer and reporting relative risks (RRs) of prostate cancer across at least three categories of circulating 25[OH]D levels were eligible for the meta-analysis. Case–control studies, cross-sectional studies, and retrospective cohort studies were excluded. Studies without RRs of prostate cancer across at least three categories of 25[OH]D concentrations were also excluded. Studies containing overlapping data were also excluded.