title: Vitamin D and type 2 diabetes.
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.
authors.affiliation: Department of Internal Medicine, Endocrine Section, VU University Medical Center, 1007 MB Amsterdam, The Netherlands. Electronic address: p.lips@vumc.nl.
authors.forename: Paul
authors.initials: P
authors.lastname: Lips
authors.affiliation: Department of Internal Medicine, Endocrine Section, VU University Medical Center, 1007 MB Amsterdam, The Netherlands.
authors.forename: Marelise
authors.initials: M
authors.lastname: Eekhoff
authors.affiliation: Department of Epidemiology and Biostatistics, VU University Medical Center, 1007 MB Amsterdam, The Netherlands.
authors.forename: Natasja
authors.initials: N
authors.lastname: van Schoor
authors.affiliation: Department of Internal Medicine, Endocrine Section, VU University Medical Center, 1007 MB Amsterdam, The Netherlands; Department of Internal Medicine, Catharina Hospital, 5623 EJ Eindhoven, The Netherlands.
authors.forename: Mirjam
authors.initials: M
authors.lastname: Oosterwerff
authors.affiliation: Department of Internal Medicine, Endocrine Section, VU University Medical Center, 1007 MB Amsterdam, The Netherlands.
authors.forename: Renate
authors.initials: R
authors.lastname: de Jongh
authors.affiliation: Department of Internal Medicine, Medical Center Alkmaar, 1800 AM Alkmaar, The Netherlands.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Krul-Poel
authors.affiliation: Department of Internal Medicine, Endocrine Section, VU University Medical Center, 1007 MB Amsterdam, The Netherlands; Department of Internal Medicine, Medical Center Alkmaar, 1800 AM Alkmaar, The Netherlands.
authors.forename: Suat
authors.initials: S
authors.lastname: Simsek
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000032:analysis / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000188:drug therapy / Q000209:etiology / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D016032:Randomized Controlled Trials as Topic; D014807:Vitamin D / Q000378:metabolism* / Q000627:therapeutic use; D014808:Vitamin D Deficiency / Q000097:blood / Q000150:complications / Q000188:drug therapy / Q000378:metabolism*; D014815:Vitamins / Q000378:metabolism / Q000627:therapeutic use
chemical_list: D001786:Blood Glucose; D007328:Insulin; D014815:Vitamins; D014807:Vitamin D
keywords: Impaired fasting glucose; Impaired glucose tolerance; Insulin resistance; Type 2 diabetes; Vitamin D deficiency; Vitamin D supplementation; β-cell function