The Effect of Vitamin D Supplementation on Glucose Metabolism in Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis of Intervention Studies

J Diabetes Complications. 2017 Jul;31(7):1115-1126. doi: 10.1016/j.jdiacomp.2017.04.019. Epub 2017 Apr 21.


Aims: We aimed to assess whether vitamin D supplementation improves glucose metabolism in adults with type 2 diabetes.

Methods: PubMed and Cochrane database were searched up to July 1st 2016 for randomized controlled trials that assessed the relationship between vitamin D supplementation and glucose metabolism (change in hemoglobin A1C (HbA1C) and fasting blood glucose (FBG)) among adults with type 2 diabetes.

Results: Twenty nine trials (3324 participants) were included in the systematic review. Among 22 studies included in the meta-analysis, 19 reported HbA1C, 16 reported FBG outcomes and 15 were deemed poor quality. There was a modest reduction in HbA1C (-0.32% [-0.53 to -0.10], I2=91.9%) compared to placebo after vitamin D supplementation but no effect on FBG (-2.33mg/dl [-6.62 to 1.95], I2=59.2%). In studies achieving repletion of vitamin D deficiency (n=7), there were greater mean reductions in HbA1C (-0.45%, [-1.09 to 0.20]) and FBG (-7.64mg/dl [-16.25 to 0.97]) although not significant.

Conclusions: We found a modest reduction of HbA1C after vitamin D treatment in adults with type 2 diabetes albeit with substantial heterogeneity between studies and no difference in FBG. Larger studies are needed to further evaluate the glycemic effects of vitamin D treatment especially in patients with vitamin D deficiency.

Keywords: Glucose metabolism; Randomized controlled trials; Systematic review; Type 2 diabetes; Vitamin D.

Publication types

  • Meta-Analysis
  • Review
  • Systematic Review

MeSH terms

  • Blood Glucose / analysis
  • Combined Modality Therapy
  • Diabetes Mellitus, Type 2 / complications
  • Diabetes Mellitus, Type 2 / diet therapy*
  • Diabetes Mellitus, Type 2 / drug therapy
  • Diabetes Mellitus, Type 2 / metabolism
  • Dietary Supplements*
  • Evidence-Based Medicine*
  • Glycated Hemoglobin A / analysis
  • Humans
  • Hyperglycemia / prevention & control*
  • Hypoglycemia / prevention & control*
  • Hypoglycemic Agents / therapeutic use
  • Randomized Controlled Trials as Topic
  • Reproducibility of Results
  • Vitamin D / analogs & derivatives
  • Vitamin D / blood
  • Vitamin D / therapeutic use*
  • Vitamin D Deficiency / blood
  • Vitamin D Deficiency / complications
  • Vitamin D Deficiency / diet therapy


  • Blood Glucose
  • Glycated Hemoglobin A
  • Hypoglycemic Agents
  • hemoglobin A1c protein, human
  • Vitamin D
  • 25-hydroxyvitamin D