Dairy intake and 1,25-dihydroxyvitamin D levels in men at high risk for prostate cancer.

OBJECTIVE: Dairy food intake has been associated with prostate cancer in previous work, but the mechanism by which this occurs is unknown. Dairy calcium may suppress circulating levels of potentially cancer-protective 1,25-hydroxyvitamin D (1,25(OH)2D). We examined the associations of dairy, milk, calcium, and vitamin D intake with plasma 1,25(OH)2D levels among 296 men (194 black, 102 non-black) enrolled in a high risk program for prostate cancer from 10/96 to 10/07. METHODS: All participants completed diet and health history questionnaires and provided plasma samples, which were assessed for levels of 25-hydroxyvitamin D and 1,25(OH)2D. We used multivariate linear regression to examine associations with 1,25(OH)2D. RESULTS: After adjustment for age, race, energy intake, BMI, and alcohol intake, we observed no associations for any of our variables of interest with 1,25(OH)2D, or any meaningful differences in estimates by race or vitamin D status. CONCLUSION: Our findings, in a sample including a large proportion of black participants, do not confirm previous findings showing an inverse association between calcium intake and 1,25(OH)2D levels. As such, they suggest that future work should explore other mechanisms by which dairy foods and calcium might increase prostate cancer risk.