Vitamin D and type 2 diabetes: a systematic review

Eur J Clin Nutr. 2011 Sep;65(9):1005-15. doi: 10.1038/ejcn.2011.118. Epub 2011 Jul 6.

Abstract

Background/objectives: Vitamin D may modify the risk of type 2 diabetes mellitus. The aim of this review was to examine the association between vitamin D status and incident type 2 diabetes, and the effect of vitamin D supplementation on glycemic outcomes.

Methods: We performed a systematic review of English-language studies using MEDLINE through February 2011. Longitudinal cohort studies reporting associations between vitamin D status and incident type 2 diabetes, and randomized controlled trials (RCTs) of vitamin D supplementation, were included. Study characteristics and results were extracted, and study quality was assessed.

Results: A total of 8 observational cohort studies and 11 RCTs were included. In meta-analyses of observational studies, vitamin D intake>500 international units (IU)/day decreased the risk of type 2 diabetes by 13% compared with vitamin D intake<200 IU/day. Individuals with the highest vitamin D status (>25 ng/ml) had a 43% lower risk of developing type 2 diabetes (95% confidence interval 24, 57%) compared with those in the lowest group (<14 ng/ml). In post hoc analyses from eight trials among participants with normal glucose tolerance at baseline and in three small underpowered (n=32-62) trials of patients with established type 2 diabetes, there was no effect of vitamin D supplementation on glycemic outcomes. In two trials among patients with baseline glucose intolerance, vitamin D supplementation improved insulin resistance.

Conclusions: Vitamin D may play a role in type 2 diabetes; however, to better define the role of vitamin D in the development and progression of type 2 diabetes, high-quality observational studies and RCTs that measure blood 25-hydroxyvitamin D concentration and clinically relevant glycemic outcomes are needed.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Review
  • Systematic Review

MeSH terms

  • Blood Glucose / analysis
  • Calcium, Dietary / administration & dosage
  • Data Interpretation, Statistical
  • Diabetes Mellitus, Type 2 / drug therapy*
  • Diabetes Mellitus, Type 2 / epidemiology*
  • Dietary Supplements*
  • Glucose Intolerance
  • Humans
  • Insulin Resistance
  • Meta-Analysis as Topic
  • Randomized Controlled Trials as Topic
  • Vitamin D / administration & dosage
  • Vitamin D / blood*
  • Vitamins / administration & dosage
  • Vitamins / blood*

Substances

  • Blood Glucose
  • Calcium, Dietary
  • Vitamins
  • Vitamin D