Serum 25-hydroxyvitamin D [25(OH)D3] is a well-established marker for vitamin D status of the human body. In addition to the general importance of vitamin D for bone health, low serum 25(OH)D3 concentrations have been associated with increased risk of several health outcomes, such as autoimmune diseases, type 2 diabetes and cardiovascular complications. However, there is significant inter-individual variation in the average serum 25(OH)D3 concentrations and also in the response to supplementation with vitamin D. Genetic and epigenetic factors have been suggested to be responsible for a large part of the variation, but currently there is little information about the health effects of the variation.~In our previous study (VitDmet, Clinicaltrials.gov NCT01479933) we showed that only half of the participants responded to the 5-month vitamin D3 supplementation of 40 µg/day or 80 µg/day as expected and that certain vitamin D receptor (VDR) target genes were suitable biomarkers for displaying the transcriptomic response of human tissues to vitamin D3 supplementation.~The purpose of the current study is to investigate whether a high-dose vitamin D3 oral bolus produces marked VDR target gene expression response and whether there is large inter-individual variation, as what was suggested with the 5-month lower-dose supplementation.~In the Trial 1, the subjects are randomized to receive either 2,000 micrograms (80 000 IU) of vitamin D3 (n=20) or placebo (n=10) in one day. Blood samples are collected for peripheral blood mononuclear cell isolation and serum 25(OH)D3 measurements at baseline and 24 h and 48 h and 30 days after the first dose. Blood samples are also collected for immunomarker analyses. In the Trial 2, the procedures of the Trial 1 are repeated in two subjects with known low and high serum 25(OH)D3 concentrations in order to investigate more specifically the impact of different starting levels of serum 25(OH)D3.~In February 2015, new subjects were recruited to enter the Trial 1 in order to increase the size of the study. All the new subjects received the 2,000 microgram bolus of vitamin D3, there were no new subjects in the placebo arm.~June 30, 2016. Change to protocol: There will be no Trial 2, but instead the blood samples obtained in the Trial 1 from up to six subjects will be used for the additional analyses. The subjects are selected based on the response to vitamin D supplementation in the Trial 1.
The purpose of the study is to investigate whether a high-dose vitamin D3 oral bolus (2000 micrograms) produces marked vitamin D receptor target gene expression response and whether there is large inter-individual variation.