GC and type 2 diabetes mellitus: Studies have shown that vitamin D deficiency is associated with the development of T2D, T2D nephropathy, T2D microvascular or macrovascular disease, diabetic retinopathy, and diabetic peripheral neuropathy.[44–48] In an 11-year cohort follow-up study, baseline vitamin D levels were negatively correlated with the development of T2D.[49] The genetic polymorphisms of vitamin D binding protein and vitamin D receptor are associated with genetic susceptibility to T2D.