Vitamin D deficiency in the aetiology of obesity‐related insulin resistance

Summary The obese insulin‐resistant state is often associated with low circulating concentration of vitamin D 25‐hydroxyvitamin D 3 [25(OH)D 3 ]. Fat sequestration of vitamin D in the expanded obese adipose tissue mass has been pointed out as a plausible explanation for this circulating vitamin D deficiency. However, the putative mechanisms behind this hypovitaminosis D remain to be elucidated. The presence of vitamin D receptor and vitamin D–metabolizing enzymes in insulin‐sensitive organs suggests that vitamin D may be involved in glucose and lipid metabolism and may be related to insulin sensitivity. Indeed, mainly in vitro studies support a role of vitamin D in regulating glucose and lipid metabolism in several insulin‐sensitive tissues including adipose tissue, skeletal muscle, liver, as well as pancreatic insulin secretion. A potential role of vitamin D in gut barrier function and metabolism has also been suggested. This review summarizes recent knowledge on vitamin D deficiency in the aetiology of obesity‐related insulin resistance and discusses potential underlying mechanisms. Finally, the role of vitamin D supplementation on insulin sensitivity and glycaemic control is discussed.