Importance of Dosing Regimen for the Effect of Vitamin D Supplementation

Vitamin D is a hormone with effects not only on the skeleton, but on most tissues in the body. Lack of vitamin D is associated with cardio-vascular disease (CVD), type 2 diabetes, cancer, infectious and immunological diseases, as well as risk factors for these diseases. However, intervention studies with vitamin D have been inconclusive regarding diseases and risk factors. This could be due to inclusion of subjects already vitamin D sufficient, and short and underpowered studies. In addition, there are indications that the dosing regimens may be important, so that daily doses with vitamin D are more efficient than intermittent doses, which so far have been generally used. This could be related to the concentration of circulating and thereby intracellular vitamin D concentrations, which probably is dependent on daily vitamin D doses. This will be tested in the present study where 60 subjects will be randomized to vitamin D 160 000 once, vitamin D 4000 IU/day, or placebo for four weeks. The primary endpoints will be effects on serum hepcidin and plasma cathelicidin after 4 weeks, with effects on serum PTH, RNA expression and microRNA in peripheral blood, telomerase activity in peripheral blood mononuclear cells and the ration between serum 1,25(OH)2D and 24,25(OH)2D as secondary endpoints.