Free 25-hydroxyvitamin D is low in obesity, but there are no adverse associations with bone health

Walsh, Jennifer S, Evans, Amy L, Bowles, Simon, Naylor, Kim E, Jones, Kerry S, Schoenmakers, Inez, Jacques, Richard M and Eastell, Richard (2016) Free 25-hydroxyvitamin D is low in obesity, but there are no adverse associations with bone health. American Journal of Clinical Nutrition, 103 (6). pp. 1465-1471. ISSN 0002-9165

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Abstract

Background: The mechanism and clinical significance of low circulating 25-hydroxyvitamin D [25(OH)D] in obese people are unknown. Low total 25(OH)D may be due to low vitamin D–binding proteins (DBPs) or faster metabolic clearance. However, obese people have a higher bone mineral density (BMD), which suggests that low 25(OH)D may not be associated with adverse consequences for bone. Objective: We sought to determine whether 1) vitamin D metabolism and 2) its association with bone health differ by body weight. Design: We conducted a cross-sectional observational study of 223 normal-weight, overweight, and obese men and women aged 25–75 y in South Yorkshire, United Kingdom, in the fall and spring. A subgroup of 106 subjects was also assessed in the winter. We used novel techniques, including an immunoassay for free 25(OH)D, a stable isotope for the 25(OH)D3 half-life, and high-resolution quantitative tomography, to make a detailed assessment of vitamin D physiology and bone health. Results: Serum total 25(OH)D was lower in obese and overweight subjects than in normal-weight subjects in the fall and spring (geometric means: 45.0 and 40.8 compared with 58.6 nmol/L, respectively; P < 0.001) but not in the winter. Serum 25(OH)D was inversely correlated with body mass index (BMI) in the fall and spring and in the winter. Free 25(OH)D and 1,25-dihydroxyvitamin D [1,25(OH)2D] were lower in obese subjects. DBP, the DBP genotype, and the 25(OH)D3 half-life did not differ between BMI groups. Bone turnover was lower, and bone density was higher, in obese people. Conclusions: Total and free 25(OH)D and 1,25(OH)2D are lower at higher BMI, which cannot be explained by lower DBP or the shorter half-life of 25(OH)D3. We speculate that low 25(OH)D in obesity is due to a greater pool of distribution. Lower 25(OH)D may not reflect at-risk skeletal health in obese people, and BMI should be considered when interpreting serum 25(OH)D as a marker of vitamin D status.

Item Type: Article
Additional Information: © 2016 American Society for Nutrition.
Uncontrolled Keywords: bone density,bone turnover,half-life,obesity,vitamin d,vitamin d–binding protein
Faculty \ School: Faculty of Medicine and Health Sciences > Norwich Medical School
Depositing User: Pure Connector
Date Deposited: 29 Sep 2016 12:00
Last Modified: 24 Jul 2019 22:45
URI: https://ueaeprints.uea.ac.uk/id/eprint/60628
DOI: 10.3945/ajcn.115.120139

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