title: Clinical review: Effect of vitamin D3 supplementation on improving glucose homeostasis and preventing diabetes: a systematic review and meta-analysis.
abstract: BACKGROUND
  Observational studies report consistent associations between low vitamin D concentration and increased glycemia and risk of type 2 diabetes, but results of randomized controlled trials (RCTs) are mixed.
  
  
  OBJECTIVE
  The objective of the study was to systematically review RCTs that report on the effects of vitamin D supplementation on glucose homeostasis or diabetes prevention.
  
  
  METHODS
  Sources of data for the study were MEDLINE, EMBASE, SCOPUS, Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects, Health Technology Assessment, and Science Citation Index from inception to June 2013.
  
  
  METHODS
  Study selection was trials that compared vitamin D3 supplementation with placebo or a non-vitamin D supplement in adults with normal glucose tolerance, prediabetes, or type 2 diabetes.
  
  
  METHODS
  Two reviewers collected data and assessed trial quality using the Cochrane Risk of Bias tool. Random-effects models were used to estimate mean differences (MDs) and odds ratios. The main outcomes of interest were homeostasis model assessment of insulin resistance, homeostasis model assessment of β-cell function, hemoglobin A1c levels, fasting blood glucose, incident diabetes, and adverse events.
  
  
  RESULTS
  Thirty-five trials (43 407 patients) with variable risk of bias were included. Vitamin D had no significant effects on insulin resistance [homeostasis model assessment of insulin resistance: MD -0.04; 95% confidence interval (CI) -0.30 to 0.22, I-squared statistic (I(2)) = 45%], insulin secretion (homeostasis model of β-cell function: MD 1.64; 95% CI -25.94 to 29.22, I(2) = 40%), or hemoglobin A1c (MD -0.05%; 95% CI -0.12 to 0.03, I(2) = 55%) compared with controls. Four RCTs reported on the progression to new diabetes and found no effect of vitamin D (odds ratio 1.02; 95% CI 0.94 to 1.10, I(2) = 0%). Adverse events were rare, and there was no evidence of publication bias.
  
  
  CONCLUSIONS
  Evidence from available trials shows no effect of vitamin D3 supplementation on glucose homeostasis or diabetes prevention. Definitive conclusions may be limited in the context of the moderate degree of heterogeneity, variable risk of bias, and short-term follow-up duration of the available evidence to date.
authors: Alliance for Canadian Health Outcomes Research in Diabetes (J.C.S., I.N.C., S.R.M., L.T., J.A.J.) and Division of General Internal Medicine (S.R.M.), Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2E1; Division of Endocrinology, Diabetes & Metabolism, Tufts Medical Center (J.M., A.G.P.), Boston, Massachusetts 02111; Department of Medicine, Charles R. Drew University (M.B.D.), Los Angeles, California 90059; and Division of Endocrinology and Metabolism, University of Calgary (A.L.E., D.A.H.), Calgary, Canada T2N 1N4.
authors: Jennifer C
authors: JC
authors: Seida
authors: Joanna
authors: J
authors: Mitri
authors: Isabelle N
authors: IN
authors: Colmers
authors: Sumit R
authors: SR
authors: Majumdar
authors: Mayer B
authors: MB
authors: Davidson
authors: Alun L
authors: AL
authors: Edwards
authors: David A
authors: DA
authors: Hanley
authors: Anastassios G
authors: AG
authors: Pittas
authors: Lisa
authors: L
authors: Tjosvold
authors: Jeffrey A
authors: JA
authors: Johnson
mesh_terms: D001786:Blood Glucose / Q000378:metabolism*; D002762:Cholecalciferol / Q000008:administration & dosage*; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism / Q000517:prevention & control*; D019587:Dietary Supplements; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D011236:Prediabetic State / Q000378:metabolism / Q000517:prevention & control*; D016032:Randomized Controlled Trials as Topic; D014815:Vitamins / Q000008:administration & dosage
chemical_list: D001786:Blood Glucose; D014815:Vitamins; D002762:Cholecalciferol