Vitamin D & Insulin Sensitivity

 Effects of 6-month vitamin D supplementation on insulin sensitivity and secretion: a randomized, placebo-controlled trial.  In individuals at high risk of diabetes or with newly diagnosed type 2 diabetes, vitamin D supplementation for 6 months significantly increased peripheral insulin sensitivity and β-cell function, suggesting that it may slow metabolic deterioration in this population. 

Lemieux, P. et al.  2018.  European Journal of Endocrinology. 181(3):287-299.