VDR(vitamin d receptors) and DBP (vit d Binding protein) are present in bancreas tissues.In glucose tolerance and insulin secretion,certain allelic variations are seen with VDR and DBP.
VIT D not only regulates the ca absorption,also increases the insulin synthesis and secretion-through the direct action with pancreatic beta cell function.
some of the studies in UAE,shows that there was no significant difference between 25 OH Vit D and T2 Diabetes patients.
http://www.hindawi.com/journals/jdr/2014/869307/
according to Harvard medical school study,Boston,(2013),it was a meta analysis,showed an inverse and significant association between circulating vit d level and T2 Diabetes.,with a broad range of vit d level in diverse population.
Ref:
http://www.ncbi.nlm.nih.gov/pubmed/23613602
recently published vit d study (jan 2015) among Saudi population, showed that the supplementation increased the level of vit d effectively and also associated with a significant improvement of beta cell activity.but not a1c and insulin resistance.