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. 2011 Jul;26(7):1609-16.
doi: 10.1002/jbmr.387.

Vitamin D-binding protein modifies the vitamin D-bone mineral density relationship

Camille E Powe  1 , Catherine Ricciardi, Anders H Berg, Delger Erdenesanaa, Gina Collerone, Elizabeth Ankers, Julia Wenger, S Ananth Karumanchi, Ravi Thadhani, Ishir Bhan
Affiliations
Free PMC article

Vitamin D-binding protein modifies the vitamin D-bone mineral density relationship

Camille E Powe et al. J Bone Miner Res. 2011 Jul.
Free PMC article

Erratum in

  • J Bone Miner Res. 2012 Jun;27(6):1438

Abstract

Studies examining the relationship between total circulating 25-hydroxyvitamin D [25(OH)D] levels and bone mineral density (BMD) have yielded mixed results. Vitamin D-binding protein (DBP), the major carrier protein for 25(OH)D, may alter the biologic activity of circulating vitamin D. We hypothesized that free and bioavailable 25(OH)D, calculated from total 25(OH)D, DBP, and serum albumin levels, would be more strongly associated with BMD than levels of total 25(OH)D. We measured total 25(OH)D, DBP, and serum albumin levels in 49 healthy young adults enrolled in the Metabolic Abnormalities in College-Aged Students (MACS) study. Lumbar spine BMD was measured in all subjects using dual-energy X-ray absorptiometry. Clinical, diet, and laboratory information also was gathered at this time. We determined free and bioavailable (free + albumin-bound) 25(OH)D using previously validated formulas and examined their associations with BMD. BMD was not associated with total 25(OH)D levels (r = 0.172, p = .236). In contrast, free and bioavailable 25(OH)D levels were positively correlated with BMD (r = 0.413, p = .003 for free, r = 0.441, p = .002 for bioavailable). Bioavailable 25(OH)D levels remained independently associated with BMD in multivariate regression models adjusting for age, sex, body mass index, and race (p = .03). It is concluded that free and bioavailable 25(OH)D are more strongly correlated with BMD than total 25(OH)D. These findings have important implications for vitamin D supplementation in vitamin D-deficient states. Future studies should continue to explore the relationship between free and bioavailable 25(OH)D and health outcomes.

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Figures

Fig. 1
Fig. 1
Relationship between total and free 25(OH)D and lumbar spine BMD. DBP-bound, free, and bioavailable 25(OH)D levels were calculated from measured total 25(OH)D and DBP levels using equations adapted from Vermeulen. Total 25(OH)D and DBP-bound 25(OH)D were not associated with lumbar spine BMD. Free 25(OH)D and bioavailable 25(OH) D were positively correlated with lumbar spine BMD.
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