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

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 mu g vitamin D-3 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 (2-71 years) were allocated to receive either a vitamin D-3 supplement (20 mu g/d) or a placebo for 12 weeks. Circulating levels of vitamin D-3 metabolites such as the 25(OH)D-3 and the 24,25(OH)(2)D-3, and biomarkers of calcium and phosphate metabolism were quantified. Results: The 25(OH)D-3 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 < 0.01). In the vitamin D-3 group, the serum 25(OH)D-3 concentration increased from 38 +/- 14 nmol/L at baseline to 70 +/- 15 nmol/L and 73 +/- 16 nmol/L at weeks 8 and 12 of vitamin D-3 supplementation (p < 0.001), respectively. As a result, 94% of the vitamin D-3-supplemented participants reached 25(OH)D-3 concentrations of >= 50 nmol/L and thereof 46% attained 25(OH)D-3 levels of >= 75 nmol/L until the end of the study. The extent of the 25(OH)D-3 increase upon vitamin D-3 supplementation depended on 25(OH)D-3 baseline levels, age, body weight and circulating levels of triglycerides. In contrast to 25(OH)D-3, the response of 24,25(OH)(2)D-3 to the vitamin D-3 treatment was affected only by baseline levels of 24,25(OH)(2)D-3 and age. Conclusions: The average improvement of 25(OH)D-3 levels in individuals who received 20 mu g vitamin D-3 per day during the winter months was 41 nmol/L compared to individuals without supplementation. As a result almost all participants with the vitamin D-3 supplementation attained 25(OH)D-3 concentrations of 50 nmol/L and higher. The suitability of 24,25(OH)(2)D-3 as a marker of vitamin D status needs further investigation. (C) 2015 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.