Circulating vitamin D concentration and risk of prostate cancer: a dose-response meta-analysis of prospective studies.

Background: Though many studies have been performed to elucidate the association between circulating vitamin D and prostate cancer, no conclusive result is available. We carried out a dose-response meta-analysis to quantitatively examine the association of circulating 25-hydroxyvitamin D (25[OH]D) concentration with prostate cancer.

Methods: Only prospective studies examining the associations of circulating 25[OH]D concentration with prostate cancer were eligible for the meta-analysis. A random-effect meta-analysis was done first, to calculate the summary relative risk (RR) and 95% confidence intervals (CIs) comparing the higher concentration with the lower concentration of 25[OH]D. A dose-response meta-analysis using random-effects model was then carried out to evaluate the nonlinearity and calculate the summary RR caused per 10 ng/mL increment.

Results: Nineteen prospective cohort or nested case-control studies were included. Higher 25[OH]D concentration was significantly correlated with elevated risk of prostate cancer (RR =1.15, 95% CI 1.06-1.24). No nonlinear relationship was found between 25[OH]D concentration and risk of prostate cancer (=0.654). Dose-response meta-analysis showed that the summary RR caused per 10 ng/mL increment in circulating 25[OH]D concentration was 1.04 (95% CI 1.02-1.06). Subgroup analysis also found a modest dose-response relationship. Funnel plot and Egger's test did not detect publication bias.

Conclusion: The findings suggest that highest 25[OH]D concentration is correlated with elevated risk of prostate cancer and a modest dose-response effect exists in this association; however, more studies are needed.