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Total, Bioavailable, and Free 25(OH)D Relationship with Indices of Bone Health in Elderly: A Randomized Controlled Trial.

J Clin Endocrinol Metab. 2020 Dec 06;: Authors: El Sabeh M, Ghanem P, Al-Shaar L, Rahme M, Baddoura R, Halaby G, Singh RJ, Vanderschueren D, Bouillon R, El-Hajj Fuleihan G

CONTEXT: Questions regarding the superiority of free and bioavailable 25 hydroxy-vitamin D [25(OH)D] in predicting health outcomes remain unresolved. OBJECTIVE: This study investigates the impact of vitamin D variables, total, bioavailable or free 25(OH)D, on indices of bone and mineral metabolism, at baseline, and in response to two vitamin D doses. DESIGN: Our objectives are implemented as exploratory analyses on data collected in a 1-year, double blind, randomized controlled trial completed in July 2014. SETTING: Participants were recruited from 3 major hospitals in an ambulatory setting. PATIENTS OR OTHER PARTICIPANTS: Participants were elderly (>65 years), overweight, and had a baseline serum 25(OH)D between 10 and 30 ng/mL. 221 participants completed the study. INTERVENTION: Subjects were randomized to receive calcium and oral vitamin D3 (600IU/day or 3,750 IU/day) supplementation. RESULTS: Subjects who received the higher vitamin D dose had levels that were 1.3-1.4 folds higher than with the lower dose, for all variables (p-value < 0.001). Serum values of bioavailable and free 25(OH)D were associated with total 25(OH)D, with r values of 0.942 and 0.943, respectively (p-value <0.001). PTH was negatively associated with all vitamin D variables, with correlation coefficients ranging between -0.22 and -0.25; while calcium, and bone turnover markers (carboxy-terminal collagen crosslinks and osteocalcin) did not. Only total 25(OH)D had a positive relationship with % change BMD at the femoral neck at 12 months, while only free and bioavailable 25(OH) had a positive relationship with % change total body BMD at 12 months. CONCLUSION: Calculated free and bioavailable 25(OH)D do not appear to be superior to total 25(OH)D in predicting indices of bone health in an elderly population. PMID: 33280041 [PubMed - as supplied by publisher]

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