Differences in calcium metabolism between black and white men and women.

To determine whether environmental factors influence racial differences in calcium metabolism, the authors evaluated the influence of three factors (season, length of sunlight exposure, and diet) on calciotropic hormones, renal calcium excretion, and markers of bone turnover in an ambulatory population aged 25-36 years. Included were 109 black men, 114 white men, 95 black women, and 84 white women. Compared with white subjects, black subjects of both genders showed lower levels of serum 25-hydroxyvitamin D (25-OHD) and higher levels of serum 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. The mean winter levels of 25-OHD were 19 to 29% lower than the summer levels in all groups. The urinary calcium excretion was 26% lower in black men than in white men and was 36% lower in black women than in white women. The parathyroid hormone levels were 29% higher in black women than in white women, but no statistically significant racial differences in parathyroid hormone levels were seen in men. Bone turnover markers (serum osteocalcin, bone-specific alkaline phosphatase, urinary pyridinoline cross-link excretion) did not show consistent racial differences. Racial and gender differences in calcium excretion did not significantly correlate with differences in lifestyle or with levels of the calciotropic hormones. Environmental factors such as diet and sunlight exposure do not appear to influence racial differences in the levels of the calciotropic hormones or renal calcium excretion.