Epidemiological studies suggest that vitamin D protects against prostate cancer, although evidence is limited and inconsistent. We investigated associations of circulating total 25-hydroxyvitamin D (25(OH)D) with prostate specific antigen-detected prostate cancer in a case-control study nested within the prostate testing for cancer and treatment (ProtecT) trial. Conditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) quantifying the association between circulating total 25(OH)D and prostate cancer. In case-only analyses, we used unconditional logistic regression to quantify associations of total 25(OH)D with stage (advanced vs. localized) and Gleason grade (high-grade (≥7) vs. low-grade (7)). Predetermined categories of total 25(OH)D were defined as: high: ≥30 ng/mL; adequate: 20-30 ng/mL; insufficient: 12-20 ng/mL; deficient:12 ng/mL. Fractional polynomials were used to investigate the existence of any U-shaped relationship. We included 1,447 prostate cancer cases (153 advanced, 469 high-grade) and 1,449 healthy controls. There was evidence that men deficient in vitamin D had a 2-fold increased risk of advanced versus localized cancer (OR for deficient vs. adequate total 25(OH)D=2.33, 95% CI: 1.26, 4.28) and high-grade versus low-grade cancer (OR for deficient vs. adequate total 25(OH)D=1.78, 95% CI: 1.15, 2.77). There was no evidence of a linear association between total 25(OH)D and prostate cancer (p=0.44) or of an increased risk of prostate cancer with high and low vitamin D levels. Our study provides evidence that lower 25(OH)D concentrations were associated with more aggressive cancers (advanced versus localized cancers and high- versus low-Gleason grade), but there was no evidence of an association with overall prostate cancer risk.
