Vitamin D deficiency appears to have a very plausible relationship to type II diabetes. It is needed to maintain adequate blood levels of insulin.
Vitamin D receptors have been found in the pancreas where insulin is made, and preliminary evidence suggests that supplementation may increase insulin secretion for some people with adult-onset (type 2) diabetes.
Research found that 1,25-dihydroxyvitamin D3 deficiency inhibits the pancreatic secretion of insulin and that this effect is only partially dependent upon serum calcium levels. Diabetes is a chromic metabolism disorder characterized by hyperglycemia.
In type one diabetes, injection of insulin is mandatory because the beta cells of the pancreas produce no insulin, a hormone that moves sugar from blood to the cells. This an autoimmune disease, where immune system make antibodies to destroy islets cells that manufacture insulin.
In the case of type II diabetes, insulin may or may not be needed. It is characterized by impairment in insulin release as well as insulin resistance in muscles, fat cells and the liver.
The research shows that vitamin D needed for pancreas to release insulin. Diabetes Type II Vitamin D Deficiency