Molecular evaluation of vitamin D responsiveness of healthy young adults.

Abstract Vitamin D 3 has via its metabolites 25-hydroxyvitamin D 3 (25(OH)D 3 ) and 1α,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ) direct effects on the transcriptome and the epigenome of most human cells. In the VitDbol study we exposed 35 healthy young adults to an oral vitamin D 3 dose (2000 μg) or placebo and took blood samples directly before the supplementation as well as at days 1, 2 and 30. Within 24 h the vitamin D 3 intake raised the average serum levels of both 25(OH)D 3 and 1,25(OH) 2 D 3 by approximately 20%. However, we observed large inter-individual differences in these serum levels, reflected by the average ratios between 25(OH)D 3 and 1,25(OH) 2 D 3 concentrations ranging from 277 to 1365. Interestingly, average serum parathyroid hormone (PTH) levels increased at day 1 by some 10% but then decreased within the following four weeks to levels 5% below baseline. In peripheral blood mononuclear cells (PBMCs) that were isolated at the same time points we determined vitamin D-modulated chromatin accessibility by FAIRE-qPCR at selected genomic loci. This method is well suited to evaluate both short-term and long-term in vivo effects of vitamin D on the epigenome of human subjects. The differential vitamin D responsiveness of the VitDbol study participants was determined via individual changes in their PTH levels or chromatin accessibility in relation to alterations in 25(OH)D 3 concentrations. This led to the segregation of the subjects into 14 high, 11 mid and 10 low responders. In summary, the vitamin D responsiveness classification provides additional information compared to a vitamin D status assessment based on single 25(OH)D 3 serum measurements. The study was registered at Clinicaltrials.gov (NCT02063334).