INS and type 2 diabetes mellitus: In fact, in addition to the recognized calciotropic effects, vitamin D is essential for the modulation/regulation of the immune system, pancreas, liver, skeletal muscle and adipocytes (Table 1), and several clinical studies demonstrated that vitamin D supplementation in subjects with T2DM and metabolic syndrome improves lipid profile, glycated hemoglobin (HbA1c) and insulin sensitivity (HOMA-IR) [1].