Serum 25-hydroxyvitamin D, vitamin D binding protein, and prostate cancer risk in black men

BACKGROUND: Few studies have prospectively examined the relationship between vitamin D status and prostate cancer risk in black men, a group at high risk for both low vitamin D status and prostate cancer. METHODS: Among black men in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, we identified 226 prostate cancer cases and 452 controls matched on age at randomization (±5 years), date of blood draw (±30 days), calendar year of cohort entry, and time since baseline prostate cancer screening (±1 year). Conditional logistic regression was used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for the associations between serum 25-hydroxyvitamin D [25(OH)D], vitamin D binding protein (DBP), the 25(OH)D:DBP molar ratio, and prostate cancer risk. RESULTS: Serum 25(OH)D was not associated with overall prostate cancer (Q4 vs Q1: OR, 0.73; 95% CI, 0.40-1.33; P for trend =.25), although there were apparent inverse associations for nonaggressive disease (global P =.03, clinical stage I/II, and Gleason score <7) and among men ≥62 years old (P for interaction =.04) that were restricted to Q3. Interestingly, serum DBP was significantly inversely associated with prostate cancer risk (Q4 vs Q1: OR, 0.45; 95% CI, 0.20-1.00; P for trend =.03), whereas the 25(OH)D:DBP molar ratio was not. Results were similar when we mutually adjusted for 25(OH)D and DBP, and we found no evidence of interaction between the two. CONCLUSION: Our study suggests higher (versus lower) circulating DBP may be independently associated with a decreased prostate cancer risk in black men independent of 25(OH)D status. Cancer 2017;123:2698-704.