Vitamin D3 supplementation: Response and predictors of vitamin D3 metabolites – A randomized controlled trial

Summary Background & aims Large parts of the population are insufficiently supplied with vitamin D, in particular when endogenous synthesis is absent. Therefore many health care providers recommend the use of vitamin D supplements. The current study aimed to investigate the efficacy of an once-daily oral dose of 20 μg vitamin D3 to improve the vitamin D status and to evaluate predictors of response. Methods The study was conducted as a double-blind, randomized, placebo-controlled parallel trial from January till April 2013. In total, 105 subjects (20–71 years) were allocated to receive either a vitamin D3 supplement (20 μg/d) or a placebo for 12 weeks. Circulating levels of vitamin D3 metabolites such as the 25(OH)D3 and the 24,25(OH)2 D3 , and biomarkers of calcium and phosphate metabolism were quantified. Results The 25(OH)D3 serum concentrations in the placebo group decreased from 38 ± 15 nmol/L at baseline to 32 ± 14 nmol/L and 32 ± 13 nmol/L at weeks 8 and 12 of the study, respectively ( p