Vitamin D Deficiency Induces Insulin Resistance and Re-Supplementation Attenuates Hepatic Glucose Output via the PI3K-AKT-FOXO1 Mediated Pathway.

The results demonstrate that vitamin D deficiency induces insulin resistance. Its supplementation has significant beneficial effects on pathophysiological mechanisms in type 2 diabetes but only in lean and not in the obese phenotype. The increased subacute inflammation and insulin resistance in obesity cannot be significantly alleviated by vitamin D supplementation. This needs to be taken into consideration in the design of new clinical trials.