ABSTRACT
BACKGROUND: Increasing evidence supports the role of vitamin D (vitD) in modifying the risk to develop type 1 diabetes (T1D) and other autoimmune diseases. VitD3 might stimulate regulatory T cells (Tregs), a central player in the maintenance of self-tolerance. In addition, direct effects of vitD on ß-cell function are postulated. The aim of our study was to evaluate the effect of a high dose vitD supplementation on Tregs frequency (%Tregs) and ß-cell function assessed by a mixed meal tolerance test (MMTT) in healthy humans. METHODS: A double-blind, placebo controlled trial was performed in 59 healthy adult subjects (49% females). Subjects received oral vitD3 (140,000 IU monthly) or placebo for 3 months. %Tregs within 20,000 CD4+ T cells of peripheral blood was determined by multi-parametric FACS-analysis. A liquid MMTT was carried out before and after treatment. RESULTS: %Tregs increased significantly in the vitD group, but remained unchanged in the placebo group. Fasting C-peptide concentrations did not change significantly in either group. Similarly, the mean AUC for C-peptide after 3 months and the change in mean values from baseline to the end of the treatment were comparable in both groups. CONCLUSIONS: A short time high dose vitD3 supplementation significantly increased the frequency of Tregs, but did not further improve ß-cell function in apparently healthy subjects. The immunomodulatory potential of vitD might be an important mechanistic link for the association of vitD and T1D.