INS and type 1 diabetes mellitus: Although the two types of diabetes, type 1 diabetes (T1D) (autoimmune disease preventing the pancreas from making insulin) and type 2 diabetes (T2D) (a chronic condition characterized by the body’s inability to use insulin properly) have completely different etiologies, vitamin D is believed to have a crucial role in the pathophysiology of both the aforementioned types of the disease [118,119].