Vitamin D supplementation induces a significant decrease in Th1 and Th17 cells. Peripheral blood mononuclear cells (PBMCs) were stimulated for 4 hours with Phorbol myristate acetate (PMA) and ionomycin. After gating on CD3+ T cells, frequencies of IFN-γ-producing CD4+ (Th1) and CD8+ T cells, IL-17A-producing CD4+ T cells (Th17) and IL-4-producing CD4+ T cells (Th2) were analyzed with vitamin D supplementation. Th1, IFN-γ-producing CD8+ T cells and Th17 cells decreased after 2 months of vitamin D supplementation. Mean ± standard error of the mean (SEM) is shown. *P < 0.05, **P < 0.01, ***P < 0.001 versus Day 0; Wilcoxon test.