How Vitamin D prevents Insulin Resistance – Sept 2020

The Molecular Mechanisms by Which Vitamin D Prevents Insulin Resistance and Associated Disorders

Review Int J Mol Sci. 2020 Sep 11;21(18):E6644. doi: 10.3390/ijms21186644.
Izabela Szymczak-Pajor 1, Józef Drzewoski 2, Agnieszka Śliwińska 1

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Table of Contents

Numerous studies have shown that vitamin D deficiency is very common in modern societies and is perceived as an important risk factor in the development of insulin resistance and related diseases such as obesity and type 2 diabetes (T2DM). While it is generally accepted that vitamin D is a regulator of bone homeostasis, its ability to counteract insulin resistance is subject to debate. The goal of this communication is to review the molecular mechanism by which vitamin D reduces insulin resistance and related complications. The university library, PUBMED, and Google Scholar were searched to find relevant studies to be summarized in this review article. Insulin resistance is accompanied by chronic hyperglycaemia and inflammation. Recent studies have shown that vitamin D exhibits indirect antioxidative properties and participates in the maintenance of normal resting ROS level. Appealingly, vitamin D reduces inflammation and regulates Ca2+ level in many cell types. Therefore, the beneficial actions of vitamin D include diminished insulin resistance which is observed as an improvement of glucose and lipid metabolism in insulin-sensitive tissues.

Conclusions
Apart from mineral and bone metabolism regulation, vitamin D is also involved in a great number of cellular processes responsible for the homeostasis of glucose and lipid metabolism via insulin signaling pathway. Accumulating evidence supports that vitamin D deficiency is associated with the pathogenesis of insulin resistance. Disturbances in insulin signaling and inflammation are closely related, and vitamin D was found to reduce both of these disorders. Current evidence suggests that these benefits are the effect of vitamin D on Ca2+ and ROS homeostasis, as well as regulation of the expression of numerous genes. Considering multiple targets of vitamin D, we propose that pleiotropic action of vitamin D is a result of the crosstalk between insulin signaling and other signaling pathways governing metabolism, inflammation, immunomodulation, apoptosis, and adipogenesis. We have only just started to understand how vitamin D reduces insulin resistance and associated disorders. However, we would like to underline that although the awareness of vitamin D-associated health benefits is arising, the elevated consumption of vitamin D supplements may predispose to an increased incidence of vitamin D toxicity. Thus, without medical supervision, we advise caution for people who self-administrate higher than recommended doses of vitamin D.