Vitamin D and type 2 diabetes

J Steroid Biochem Mol Biol. 2017 Oct;173:280-285. doi: 10.1016/j.jsbmb.2016.11.021. Epub 2016 Dec 5.

Abstract

Vitamin D deficiency is associated with a decreased insulin release, insulin resistance and type 2 diabetes in experimental and epidemiological studies. Animal studies show that 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) stimulates the pancreatic β-cell to secrete insulin. The relationship between vitamin D deficiency and insulin resistance could develop through inflammation, as vitamin D deficiency is associated with increased inflammatory markers. In addition, genetic polymorphisms of vitamin D -related genes may predispose to impaired glycemic control and type 2 diabetes. Epidemiologic studies showed an association between low serum 25-hydroxyvitamin D3 (25(OH)D3) concentration and an increased risk for the metabolic syndrome and type 2 diabetes. This may be partly explained by an increased fat mass. A possible causal relationship between vitamin D deficiency and type 2 diabetes should be proven by randomized clinical trials showing that either type 2 diabetes can be prevented or insulin release and insulin sensitivity can be improved by vitamin D supplements. The results of randomized clinical trials on the effect of vitamin D versus placebo, sometimes combined with calcium, in patients with impaired glucose tolerance ("prediabetes") or type 2 diabetes are inconsistent. Some studies showed a slight decrease of fasting plasma glucose or improvement of insulin resistance, but often only in posthoc analyses. These effects are mainly visible in patients with vitamin D deficiency and impaired glucose tolerance at baseline. Meta-analyses of randomized clinical trials in general did not show significant effects of vitamin D supplementation on glycemic control. Currently, several large scale randomized clinical trials with vitamin D supplementation in doses of 1600-4000IU/d are ongoing with glycemic control or incidence of diabetes mellitus as outcome. Vitamin D deficiency needs to be prevented or cured, but until the results of these trials are published, high-dose vitamin D supplementation cannot be recommended for prevention or amelioration of type 2 diabetes.

Keywords: Impaired fasting glucose; Impaired glucose tolerance; Insulin resistance; Type 2 diabetes; Vitamin D deficiency; Vitamin D supplementation; β-cell function.

Publication types

  • Meta-Analysis
  • Review

MeSH terms

  • Animals
  • Blood Glucose / analysis
  • Blood Glucose / metabolism
  • Diabetes Mellitus, Type 2 / blood
  • Diabetes Mellitus, Type 2 / drug therapy
  • Diabetes Mellitus, Type 2 / etiology
  • Diabetes Mellitus, Type 2 / metabolism*
  • Humans
  • Insulin / metabolism
  • Randomized Controlled Trials as Topic
  • Vitamin D / metabolism*
  • Vitamin D / therapeutic use
  • Vitamin D Deficiency / blood
  • Vitamin D Deficiency / complications
  • Vitamin D Deficiency / drug therapy
  • Vitamin D Deficiency / metabolism*
  • Vitamins / metabolism
  • Vitamins / therapeutic use

Substances

  • Blood Glucose
  • Insulin
  • Vitamins
  • Vitamin D