CALCIUM, VITAMIN-D, AND PARATHYROID-HORMONE STATUS IN YOUNG WHITE AND BLACK-WOMEN - ASSOCIATION WITH RACIAL-DIFFERENCES IN BONE MASS

The etiology of the racial disparity in bone mass and fracture rate is unknown. Since the PTH-vitamin D endocrine system is a major regulator of calcium metabolism and bone turnover, this cross-sectional study examined the relationship of radial and lumbar bone density to vitamin D metabolite and PTH concentrations and to calcium intake and excretion in 67 white and 70 black highly comparable, healthy, premenopausal women. Bone density at both radial and lumbar sites was higher in blacks than in whites. Serum 25-hydroxyvitamin D was slightly but not statistically significantly (P = 0.08), lower in blacks than in whites, but there were no racial differences in 1,25-dihydroxyvitamin D, PTH, or renal tubular maximum for reabsorption of phosphate. The mean 25-hydroxyvitamin D concentration in blacks was well within the normal range and was not associated with evidence of secondary hyperparathyroidism. There were no correlations of bone density to vitamin D or PTH concentrations. Although there were no racial differences in dietary intake of calcium and vitamin D or in sodium excretion, 24-h urinary calcium excretion was significantly lower in blacks than in whites, and calcium excretion was inversely associated with radial bone density. In contrast to previous reports, in healthy, normal weight, premenopausal black women there is no evidence of vitamin D deficiency or secondary hyperparathyroidism, suggesting that factors other than the vitamin D-PTH axis are responsible for racial differences in bone mass.