University of Oulu

Saarnio E, Pekkinen M, Itkonen ST, Kemi V, Karp H, Ivaska KK, et al. (2018) Low free 25-hydroxyvitamin D and high vitamin D binding protein and parathyroid hormone in obese Caucasians. A complex association with bone? PLoS ONE 13(2): e0192596.

Low free 25-hydroxyvitamin D and high vitamin D binding protein and parathyroid hormone in obese Caucasians : a complex association with bone?

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Author: Saarnio, Elisa1; Pekkinen, Minna2,3; Itkonen, Suvi T.1;
Organizations: 1Calcium Research Unit, Department of Food and Nutrition, University of Helsinki, Helsinki, Finland
2Folkhälsan Institute of Genetics, Folkhälsan Research Center, Helsinki, Finland
3Children’s Hospital, Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland
4Department of Cell Biology and Anatomy, Institute of Biomedicine, University of Turku, Turku, Finland
5Department of Clinical Chemistry, University of Oulu, Oulu, Finland
6Northern Finland Laboratory Centre Nordlab, Oulu, Finland
7Medical Research Center, Oulu, Finland
8Tykslab, the Hospital District of Southwest Finland, Turku, Finland
9Department of Clinical Chemistry, University Hospital Turku, Turku, Finland
10The UKK Institute for Health Promotion Research, Tampere, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.3 MB)
Persistent link:
Language: English
Published: Public Library of Science, 2018
Publish Date: 2018-04-16


Background: Studies have shown altered vitamin D metabolism in obesity. We assessed differences between obese and normal-weight subjects in total, free, and bioavailable 25-hydroxyvitamin D (25(OH)D, 25(OH)DFree, and 25(OH)DBio, respectively), vitamin D binding protein (DBP), parathyroid hormone (PTH) and bone traits.

Methods: 595 37–47-year-old healthy Finnish men and women stratified by BMI were examined in this cross-sectional study. Background characteristic and intakes of vitamin D and calcium were collected. The concentrations of 25(OH)D, PTH, DBP, albumin and bone turnover markers were determined from blood. 25(OH)DFree and 25(OH)DBio were calculated. pQCT was performed at radius and tibia.

Results: Mean±SE (ANCOVA) 25(OH)DFree (10.8±0.6 vs 12.9±0.4 nmol/L; P = 0.008) and 25(OH)DBio (4.1±0.3 vs 5.1±0.1 nmol/L; P = 0.003) were lower in obese than in normal-weight women. In men, 25(OH)D (48.0±2.4 vs 56.4±2.0 nmol/L, P = 0.003), 25(OH)DFree (10.3±0.7 vs 12.5±0.6 pmol/L; P = 0.044) and 25(OH)DBio (4.2±0.3 vs 5.1±0.2 nmol/L; P = 0.032) were lower in obese. Similarly in all subjects, 25(OH)D, 25(OH)DFree and 25(OH)DBio were lower in obese (P<0.001). DBP (399±12 vs 356±7mg/L, P = 0.008) and PTH (62.2±3.0 vs 53.3±1.9 ng/L; P = 0.045) were higher in obese than in normal-weight women. In all subjects, PTH and DBP were higher in obese (P = 0.047and P = 0.004, respectively). In obese women, 25(OH)D was negatively associated with distal radius trabecular density (R²2 = 0.089, P = 0.009) and tibial shaft cortical strength index (CSI) (R² = 0.146, P = 0.004). 25(OH)DFree was negatively associated with distal radius CSI (R² = 0.070, P = 0.049), radial shaft cortical density (CorD) (R² = 0.050, P = 0.045), and tibial shaft CSI (R² = 0.113, P = 0.012). 25(OH)DBio was negatively associated with distal radius CSI (R² = 0.072, P = 0.045), radial shaft CorD (R² = 0.059, P = 0.032), and tibial shaft CSI (R² = 0.093, P = 0.024).

Conclusions: The associations between BMI and 25(OH)D, 25(OH)DFree, and 25(OH)DBio, DBP, and PTH suggest that obese subjects may differ from normal-weight subjects in vitamin D metabolism. BMI associated positively with trabecular bone traits and CSI in our study, and slightly negatively with cortical bone traits. Surprisingly, there was a negative association of free and bioavailable 25(OH)D and some of the bone traits in obese women.

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Series: PLoS one
ISSN: 1932-6203
ISSN-E: 1932-6203
ISSN-L: 1932-6203
Volume: 13
Issue: 2
Article number: e0192596
DOI: 10.1371/journal.pone.0192596
Type of Publication: A1 Journal article – refereed
Field of Science: 3111 Biomedicine
Funding: This work was supported by the Academy of Finland (127536),; Doctoral school for Applied Biosciences, University of Helsinki Future Fund,; Finnish Cultural Foundation,; Medicinska Understödsförening Liv och Hälsa, and Alfred Kordelin Foundation,
Dataset Reference: All relevant data are within the paper and its Supporting Information files.
Copyright information: © 2018 Saarnio et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.