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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #57200
Title: CALCIUM ABSORPTION RESPONSES TO CALCITROL IN BLACK AND WHITE PREMENOPAUSAL WOMEN

Author
item DAWSON-HUGHES BE - TUFTS-HNRCA
item HARRIS SUSAN S - TUFTS-HNRCA
item FINNERAN SUSAN - TUFTS-HNRCA
item RASMUSSEN HELEN - TUFTS-HNRCA

Submitted to: Journal of Clinical Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: It is widely recognized that blacks have higher bone mass and lower fracture rates than whites but the reason(s) for this are uncertain. Understanding race differences in calcium handling is important because it may increase understanding of the race difference in bone mass. In an earlier study, we observed that black women had a similar calcium absorption as white women but higher blood levels of the active form of vitamin D that stimulates absorption, suggesting that they may have a gut resistance to the action of vitamin D. To test this, we measured calcium absorption in 11 black and 12 white healthy premenopausal women both before and after two weeks of treatment with calcitriol, the active form of vitamin D. We found that the increase in calcium absorption in response to calcitriol in the blacks was less than half that of the whites (18.4 % vs 44.6%). This finding supports the hypothesis that blacks have gut resistance to the action of active vitamin D. Further work is needed to understand how this fits with the general finding of higher skeletal mass in blacks.

Technical Abstract: On the basis of recent findings that adult black women had similar calcium absorption but higher levels of 1,25(OH)2SD than white women, we hypothesized that blacks have a gut resistance to the action of calcitriol. To test this, we studied 11 black (age 32.4 +/- 5.7 (SD)yr) and 12 white women (28.4 +/- 5.5 yr). The women were maintained on a constant 500 mg calcium diet for 4 weeks and each received calcitriol 0.25 micro g four times daily for the last two weeks. After 2 and 4 weeks, each had measurements of fractional 45-Ca absorption index and blood and urine tests. At two weeks, the black women had similar calcium absorption indices (18.7 +/- 1.9 (SEM)%/L vs 20.0 +/- 1.8%/L, age adjusted), borderline higher 1,25(OH)2SD levels (95.7 +/- 6.4 (SEM)pmol/L vs 78.2 +/- 6.2 pmol/L, P = 0.071, age adjusted), higher serum PTH levels, and lower urinary calcium excretion. Calcitriol therapy induced similar increments in plasma 1,25(OH)2SD levels in the 2 groups but a smaller increment in calcium absorption in the black women (18.4 +/- 8.6 (SEM)% vs 44.6 +/- 7.8%, P = 0.043, means adjusted for age and initial absorption index). These findings support the hypothesis that, compared with whites, healthy premenopausal black women have gut resistance to the action of calcitriol.