Determinants of vitamin D levels in men receiving androgen deprivation therapy for prostate cancer.

PURPOSE: Studies found an association between decreased 25-OH vitamin D blood level and prostate cancer progression. Vitamin D supplementation is controversial and dosage recommendations inconsistent. This study identified factors associated with 25-OH vitamin D levels and whether vitamin D supplementation with 800 IU/day raised vitamin D levels in prostate cancer patients receiving androgen deprivation therapy (ADT). DATA SOURCES: We recruited 108 men treated with ADT for ≥9 months from eight cancer and urology practices. Sections of the NHANES 2005-2006 questionnaire and Canadian Fitness Survey were completed identifying age, ethnicity, length of ADT use, calcium supplementation ≥1000 IU mg/day, body mass index, exercise, alcohol and tobacco use, and vitamin D supplementation ≥800 IU/daily. Blood was collected for 25-OH vitamin D analysis. CONCLUSIONS: The majority of men (66%) had blood levels of 25-OH vitamin D <32 ng/mL. Regression analysis showed vitamin D supplementation (ß = 6.556, CI 1.463, 11.650; p = .012) and African American ethnicity (ß = -7.816, CI -12.996, -2.635; p = .003) is associated with 25-OH vitamin D level after controlling age and tobacco use. PRACTICE IMPLICATIONS: Findings support current recommendations for supplementation with ≥800 IU vitamin D/day for men receiving ADT. Nurse practitioners caring for prostate cancer patients receiving ADT should include vitamin D monitoring and supplementation.