INS and type 2 diabetes mellitus: Both synthesized in the skin in response to sunlight exposure and/or consumed within the diet and as a supplement, 25(OH)D is the main circulating form of vitamin D. It has been linked to dysglycaemia and T2D through mechanisms that affect both insulin resistance and pancreatic β-cell insulin secretion, as well as inflammation and accumulation of advanced glycation end (AGE) products (Figure 3).