VDR and Insulin resistance: It has been hypothesized that vitamin D3 deficiency has a role in type 1 and type 2 diabetes pathogenesis; in particular, different studies highlighted the leading role of vitamin D receptor (VDR) in maintenance normoglycemia, and the alteration of VDR function has been linked to insulin resistance (Zeitz et al., 2003; Oh et al., 2015; Ni et al., 2016).