Serum 1,25-dihydroxy vitamin D is inversely associated with body mass index

Background Based on in vitro studies, it has been hypothesized that 1,25-dihydroxy vitamin D (1,25-vit D) may promote weight gain in humans, but previous studies have demonstrated conflicting results regarding the association between serum 1,25-vit D and body mass index (BMI). Aim of the study To evaluate the relation between serum 1,25-vit D and BMI. Methods Two thousand one hundred and eighty-seven subjects, recruited from a metabolic and medical lifestyle management clinic, were included in a cross-sectional study. BMI, 25-hydroxy vitamin D (25-OH-vit D) and 1,25-vit D were measured. The cohort was divided according to BMI in five groups (< 25, 25-29.9, 30-34.9, 35-39.9 and > 39.9 kg/m(2)). Statistical analyses were performed with multiple linear regression models. Age and gender were used as explanatory covariates. Results With increasing BMI group, there was a significant decrease in both serum 25-OH-vit D and 1,25-vit D (P < 0.001). Those with BMI > 39.9 kg/m(2) had 24% lower serum 25-OH-vit D levels and 18 % lower 1,25-vit D levels than those with BMI < 25 kg/m(2). Conclusions There is an inverse association between BMI and the serum levels of 25-OH-vit D and 1,25-vit D. This makes it highly unlikely that high levels of circulating 1,25-vit D contribute to the development of obesity.