title: Effects of vitamin D supplementation on endothelial function: a systematic review and meta-analysis of randomised clinical trials.
abstract: BACKGROUND
  In addition to regulating calcium homoeostasis and bone health, vitamin D influences vascular and metabolic processes including endothelial function (EF) and insulin signalling. This systematic review and meta-analysis of randomised clinical trials (RCTs) were conducted to investigate the effect of vitamin D supplementation on EF and to examine whether the effect size was modified by health status, study duration, dose, route of vitamin D administration, vitamin D status (baseline and post-intervention), body mass index (BMI), age and type of vitamin D.
  
  
  METHODS
  We searched the Medline, Embase, Cochrane Library and Scopus databases from inception until March 2015 for studies meeting the following criteria: (1) RCT with adult participants, (2) vitamin D administration alone, (3) studies that quantified EF using commonly applied methods including ultrasound, plethysmography, applanation tonometry and laser Doppler.
  
  
  RESULTS
  Sixteen articles reporting data for 1177 participants were included. Study duration ranged from 4 to 52 weeks. The effect of vitamin D on EF was not significant (SMD: 0.08, 95 % CI -0.06, 0.22, p = 0.28). Subgroup analysis showed a significant improvement of EF in diabetic subjects (SMD: 0.31, 95 % CI 0.05, 0.57, p = 0.02). A non-significant trend was found for diastolic blood pressure (β = 0.02; p = 0.07) and BMI (β = 0.05; p = 0.06).
  
  
  CONCLUSIONS
  Vitamin D supplementation did not improve EF. The significant effect of vitamin D in diabetics and a tendency for an association with BMI may indicate a role of excess adiposity and insulin resistance in modulating the effects of vitamin D on vascular function. This remains to be tested in future studies.
authors: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, NE4 5PL, UK.|Institute of Medical Science Technology, Universiti Kuala Lumpur, Kuala Lumpur, Malaysia.
authors: Azizah Mat
authors: AM
authors: Hussin
authors: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, NE4 5PL, UK.|College of Medicine, University of Al-Mustansiriyah, Baghdad, Iraq.
authors: Ammar W
authors: AW
authors: Ashor
authors: Elsie Widdowson Laboratory, MRC Human Nutrition Research, 120 Fulbourn Road, Cambridge, CB1 9NL, UK.
authors: Inez
authors: I
authors: Schoenmakers
authors: School of Agriculture, Food and Rural Development, Newcastle University, Newcastle upon Tyne, UK.
authors: Tom
authors: T
authors: Hill
authors: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, NE4 5PL, UK.
authors: John C
authors: JC
authors: Mathers
authors: Human Nutrition Research Centre, Institute of Cellular Medicine, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, NE4 5PL, UK. mario.siervo@ncl.ac.uk.|Elsie Widdowson Laboratory, MRC Human Nutrition Research, 120 Fulbourn Road, Cambridge, CB1 9NL, UK. mario.siervo@ncl.ac.uk.
authors: Mario
authors: M
authors: Siervo
mesh_terms: D001794:Blood Pressure / Q000187:drug effects; D016208:Databases, Factual; D019587:Dietary Supplements; D004727:Endothelium / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D016032:Randomized Controlled Trials as Topic; D014807:Vitamin D / Q000008:administration & dosage* / Q000097:blood*
chemical_list: D014807:Vitamin D
keywords: Cardiovascular risk; Flow-mediated dilation; Forearm blood flow; Nitric oxide; Pulse wave velocity; Vitamin D