Bone Abstracts

Objective: Although obesity is a risk factor for vitamin D insufficiency, its impact on vitamin D-binding protein (DBP) concentration, and thereby possibly also on free 25OHD, is less well known. Our aim was to compare total and free serum 25OHD, and DBP concentrations between obese and normal-weight young adults at baseline, and their responses to cholecalciferol supplementation.

Design: A 12 weeks’ randomized, double-blinded clinical trial.

Patients: Obese subjects N=18 (BMI=38, 67% men) with severe childhood-onset obesity and 24 age-matched normal-weight controls (BMI=23, 46% men), mean age 21 years. Both obese and control subjects were randomized into two groups to receive either placebo or cholecalciferol 50 μg daily.

Measurements: At baseline, 6 and 12 weeks blood samples and anthropometric measurements were collected; baseline body composition was assessed by dual-energy x-ray absorptiometry.

Results: At baseline obese subjects had, compared with controls, lower total and free serum 25OHD (49 vs 62 nmol/l, P=0.041; 2.8 vs 4.7 pg/ml, P=0.001), without differences in DBP concentrations (309 vs 346 μg/ml, P=0.212). Cholecalciferol 50 μg per day increased both total and free 25OHD (ANCOVA P<0.001 and P=0.021). The response of total 25OHD to supplementation was inferior in the obese compared with controls (P=0.027). On the contrary, the change in free 25OHD concentration was similar in groups (P=0.487).

Conclusions: Obese young adults exhibit lower total and free 25OHD concentration, which is not directly explained by differences in DBP status. The response of free 25OHD to supplementation did not differ between obese and control subjects.