Calcium absorption responses to calcitriol in black and white premenopausal women.
On the basis of recent findings that adult black women had similar calcium absorption but higher levels of 1,25-dihydroxyvitamin D [1,25-(OH)2D] 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 microgram) four times daily for the last 2 weeks. After 2 and 4 weeks, each subject had measurements of fractional 45Ca absorption index and blood and urine tests. At 2 weeks, the black women had similar calcium absorption indexes [18.7 +/- 1.9% (+/- SEM)/L vs. 20.0 +/- 1.8%/L; age adjusted], borderline higher 1,25-(OH)2D levels [95.7 +/- 6.4 (+/- SEM) 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)2D levels in the two groups, but a smaller increment in calcium absorption in the black women (18.4 +/- 8.6% 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.
Dawson-Hughes
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Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111, USA.
Harris
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Finneran
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Rasmussen
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HM
D000328:Adult; D001741:Black or African American; D044383:Black People; D002112:Calcifediol / Q000097:blood; D002117:Calcitriol / Q000097:blood / Q000494:pharmacology*; D002118:Calcium / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D002136:Calcium, Dietary; D005260:Female; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects*; D015675:Osteocalcin / Q000097:blood; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood; D017697:Premenopause; D014481:United States; D044465:White People
D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D010710:Phosphates; D015675:Osteocalcin; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium