Vitamin D in Diabetes: Uncovering the Sunshine Hormone's Role in Glucose Metabolism and Beyond

Over the last decades, epidemiology and functional studies have started to reveal a pivotal role of vitamin D in both type 1 and type 2 diabetes pathogenesis. Acting through the vitamin D receptor (VDR), vitamin D regulates insulin secretion in pancreatic islets and insulin sensitivity in multiple peripheral metabolic organs. In vitro studies and both T1D and T2D animal models showed that vitamin D can improve glucose homeostasis by enhancing insulin secretion, reducing inflammation, reducing autoimmunity, preserving beta cell mass, and sensitizing insulin action. Conversely, vitamin D deficiency has been shown relevant in increasing T1D and T2D incidence. While clinical trials testing the hypothesis that vitamin D improves glycemia in T2D have shown conflicting results, subgroup and meta-analyses support the idea that raising serum vitamin D levels may reduce the progression from prediabetes to T2D. In this review, we summarize current knowledge on the molecular mechanisms of vitamin D in insulin secretion, insulin sensitivity, and immunity, as well as the observational and interventional human studies investigating the use of vitamin D as a treatment for diabetes.

Automated summary

In recent decades, research has shown that vitamin D plays a significant role in the development of both type 1 and type 2 diabetes. Through the vitamin D receptor, it regulates insulin secretion and insulin sensitivity in various organs, improving glucose balance. Vitamin D deficiency, on the other hand, has been linked to increased incidence of both types of diabetes. Clinical trials have had conflicting results on whether vitamin D improves glycemia in type 2 diabetes, but meta-analyses suggest that raising serum vitamin D levels may reduce the progression from prediabetes to type 2 diabetes. This review summarizes current knowledge on the molecular mechanisms of vitamin D in insulin secretion, insulin sensitivity, and immunity, as well as the use of vitamin D as a treatment for diabetes in human studies.