Increased vitamin D-binding protein and decreased free 25(OH)D in obese women of reproductive age

Abstract

Obese subjects have lower circulating 25-hydroxyvitamin D (25(OH)D) than normal-weight subjects. Knowledge is scarce regarding differences in vitamin D-binding protein (DBP), free 25(OH)D, and intake of vitamin D between normal-weight and obese subjects. The purpose of this study was to examine intake and vitamin D status in obese compared with normal-weight women. Between September 2009 and October 2011, 43 obese and 43 normal-weight women, 22-45 years of age, mean BMI of 39.1 ± 4.6 and 21.6 ± 1.8 kg/m(2), respectively, were recruited in the western Sweden region (latitude 57°N). Blood samples, data regarding diet, and sun exposure were collected. DBP concentrations were 320 ± 121 and 266 ± 104 μg/mL (P = 0.02) in obese and normal-weight women, respectively. Calculated free 25(OH)D was 13.3 ± 5.5 (obese) and 23.7 ± 10.7 (normal-weight) (P < 0.001). The obese women had a 20.1 nmol/L lower mean 25(HO)D concentration compared to normal-weight women (P < 0.001). 56 % of obese women and 12 % of normal-weight women had 25(OH)D concentrations ≤50 nmol/L. There was no statistically significant difference in total vitamin D intake between the groups. 39 % of the women had a total vitamin D intake <7.5 μg/day, the current national recommendation for vitamin D in Sweden. Obese women had higher DBP concentrations compared with normal-weight women and lower free 25(OH)D. The obese women were more likely to have 25(OH)D concentrations that could be considered suboptimal. Vitamin D intake was generally low in normal-weight and obese women of childbearing age.