The relationship between obesity and the increase in serum 25(OH)D levels in response to vitamin D supplementation

Abstract

This study examines the relationship between obesity and the increase in serum 25(OH)D levels in response to vitamin D supplementation among adults with baseline serum 25(OH)D levels<50 nmol/L. This study revealed that the increase in serum 25(OH)D in response to vitamin D supplementation was higher in lean subjects as compared to obese subjects. Serum 25(OH)D is lower among obese than non-obese. This study examines the relationship between obesity and the increase in serum 25(OH)D in response to vitamin D supplementation in a large sample of adults with baseline serum 25(OH)D<50 nmol/L, relatively long average treatment duration and large average daily cholecalciferol. The computerized database of the Clalit Health Services, which the largest nonprofit health maintenance organization in Israel, was retrospectively searched for all subjects aged≥20 years who performed serum 25(OH)D test in 2011. Subjects with more than one test at different occasions in 2011 were identified and were included if the result of the first test was <50 nmol/L, and were treated with cholecalciferol between the first and the last test in 2011 (n=16,540 subjects). The mean increase in serum 25(OH)D level after treatment was 28.7 (95% confidence interval (CI), 28.0-29.4) nmol/L, 23.6 (23.0-24.2) nmol/L, and 20.1 (19.6-20.6) nmol/L in subject with BMI of <25, 25-29.9, and ≥30 kg/m2, respectively (P<0.001). The results were similar after adjustment for the potential confounders. Similarly, the proportion of subjects who achieved serum 25(OH)D≥50 nmol/L after treatment was inversely associated with BMI; 65.1, 58.3, and 49.1% for BMI of <25, 25-29.9, and ≥30 kg/m2, respectively. Compared to BMI of ≥30 kg/m2, the adjusted odds ratio for achieving levels of ≥50 nmol/L were 2.12 (95 % CI, 1.94-2.31) and 1.42 (1.31-1.54) for BMI of <25 kg/m2, and BMI of 25-29.9 kg/m2, respectively. BMI is inversely associated with the increase in serum 25(OH)D levels in response to vitamin D supplementation.