Biochemical responses of bone metabolism to 1,25-dihydroxyvitamin D administration in black and white women

The basis for the racial difference in bone mass between black and white wo men is not known. Lower bone turnover, better renal calcium conservation, a nd decreased sensitivity to parathyroid hormone (PTH) have been proposed as explanations. A dynamic comparison of osteoblast function, utilizing stimu lation by 1,25-dihydroxyvitamin D [1,25(OH)(2)D], has not been tested betwe en these two ethnic groups. We compared well-matched black (n = 15) and whi te (n = 15) premenopausal women, before and during 5 days of 1,25(OH)(2)D a dministration (1.0 mu g/day) in order to assess dynamic indices of bone met abolism. As expected, at baseline, black women had lower levels of serum 25 -hydroxyvitamin D and biochemical markers of bone turnover with slightly hi gher levels of PTH. Black women also had superior renal calcium conservatio n than white women at baseline. In response to 1,25(OH)(2)D administration, black women had a slightly greater increase in serum calcium and greater d ecrement in PTH. Moreover, black women showed a lesser increment in urinary calcium than white women and a more robust increase in two markers of bone formation osteocalcin and carboxyterminal propeptide of type procollagen - than white women. There were no changes in bone resorption indices in eith er race upon 1,25(OH)(2)D administration, These data provide preliminary ev idence that black women conserve calcium more efficiently under both static and dynamic conditions, and also appear to have better osteoblastic functi onal reserve than white women.