Vitamin D supplementation induces a preferential increase of naïve CD4+ T cells and a decrease of memory B cells. Peripheral blood mononuclear cells (PBMCs) in the lymphocyte light-scatter gate were analyzed for T cell subsets using CD3, CD4, CD45RA and CD62L staining, and for B cell subsets using CD19, CD27 and IgD staining. (A) Time evolution of CD4+ and CD8+ T cell subsets. The T cell population includes naive (N; CD45RA+CD62L+), central memory (CM; CD45RA-CD62L+), effector memory and effector (EM; CD45RA-CD62L-), and terminally differentiated effector (TE; CD45RA+CD62L-). (B) Time evolution of CD19+ B cell subsets. The B cell population includes naive (N; IgD+CD27-), marginal zone-like (MZ; IgD+CD27+), class-switched memory (CS IgD-CD27+), and IgD-CD27- B cells. Peripheral blood naïve CD4+ T cells increased and IgD-CD27- memory B cells decreased under 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.