SUMMARY: Among 307 males seen in VA Medical Center, independent determinants (p < 0.01 for all) of serum 25-hydroxyvitamin D [25(OH)D] levels included race, vitamin D supplements, BMI, dietary calcium intake and smoking, but not age. Negative association between 25(OH)D and parathyroid hormone (PTH) was similar for Caucasian and African-American men. INTRODUCTION: In this prospective cohort study, we examined determinants of serum 25-hydroxyvitamin D [25(OH)D] levels and the relationship between 25(OH)D and PTH levels and body mass index (BMI). METHODS: Male veterans (n = 307) were recruited at a VA Medical Center. Serum levels of PTH and 25(OH)D were obtained. Surveys and chart reviews were completed. Vitamin D insufficiency was defined as 25(OH)D <30 ng/ml. Univariate and multivariate regression analyses were performed. RESULTS: Among 232 African-American (AA) men (mean +/- SD), 25(OH)D level (21.4 +/- 10.4 ng/ml) was lower and prevalence of insufficiency (80%) was higher than among 75 Caucasians (C; 28.5 +/- 11.1 ng/ml and 53%, respectively, p < 0.01 for both). In multivariate regression analysis, independent determinants (p < 0.01 for all) of 25(OH)D levels included AA race, vitamin D supplements, BMI, dietary calcium intake, and smoking. Despite lower 25(OH)D levels in African-Americans, PTH levels were similar to those seen in Caucasians. There was a significant (p < 0.02) negative linear association between 25(OH)D and PTH in African-American (r(2) = 0.05) and Caucasian (r(2) = 0.08) men, and there was no difference between the slopes of the relationship. CONCLUSIONS: 25(OH)D levels are determined by modifiable risk factors such as vitamin D supplementation in both AA and C males. The negative association between 25(OH)D and PTH is similar between the two races.