Effects of Race on Diurnal Patterns of Renal Conservation of Calcium and Bone Resorption in Premenopausal Women |
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Authors: | N H Bell B T Williamson B W Hollis B L Riggs |
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Institution: | (1) Department of Medicine, US;(2) Department of Pharmacology, US;(3) Department of Pediatrics, Medical University of South Carolina, Charleston;, US;(4) Endocrine Research Unit, Mayo Clinic and Mayo Foundation, Rochester, USA, US |
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Abstract: | Previous studies showed differences in bone and mineral metabolism in African-Americans and Caucasians: reductions in serum
25-hydroxyvitamin D 25(OH)D], urinary calcium and skeletal remodeling and moderate secondary hyperparathyroidism. Diurnal
studies were carried out in 7 African-American and 7 white normal premenopausal women matched for age, weight and height to
further characterize these racial differences in calcium homeostasis. Serum 25(OH)D was significantly lower and serum intact
parathyroid hormone (PTH) was significantly higher in the African-American compared with the white women, whereas serum total
calcium, Ca2+, phosphorus and 1,25-dihydroxyvitamin D 1,25(OH)2D] were not different in the two groups. Serum intact PTH increased significantly at night in the white women and did not
change in the African-American women. Urinary calcium was 47% lower in the African-American than in the white women during
the day but was not different at night. Urinary calcium declined at night by 53% in the white women and by 40% in the African-American
women. Stepwise multivariate analysis showed that determinants of urinary calcium were mean 24 h serum intact PTH and serum
Ca2+ in the two groups together, mean 24 h serum intact PTH, body mass index (BMI) and serum 25(OH)D in the white women, and BMI
in the African-American women. Urinary N-telopeptide of type I collagen, a marker of bone resorption, increased by over 60%
at night in both groups and was 25% lower in African-American compared with white women, but the difference was not statistically
different. Urinary free deoxypyridinoline also increased at night in both groups and was not racially different. Thus, African-American
women show higher serum intact PTH and greater conservation of calcium than white women throughout the day. In both groups,
maintenance of serum calcium at night is achieved by increased bone resorption and renal conservation of calcium.
Received: 15 April 1999 / Accepted: 6 July 1999 |
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Keywords: | :African American – Bone resorption – Calcium – Caucasian – Parathyroid hormone – Phosphorus |
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