Available high- quality RCTs did not support a beneficial effect of cholecalciferol on systemic IL-6 and CRP .
A systematic review protocol examining the effect of vitamin D supplementation on endothelial function
Introduction Vitamin D has potential benefits for extraskeletal health . These could include an anti-inflammatory effect as well as a reduction in endothelial dysfunction . We aim to provide quality evidence for the hypothesis that supplementation with vitamin D will improve endothelial function ( EF ) , possibly through the abrogation of systemic inflammation . Methods and analysis We will conduct a systematic review of all r and omised controlled trials on  vitamin D supplementation and EF lasting 12 weeks or more . The search will cover the period 2000–2015 and include studies that describe direct measures of EF  , markers of endothelial cell ( EC ) activation  and if concurrently reported , indicators of systemic inflammation  . Study selection will follow the Preferred Reporting Items for Systematic Review s and Meta-Analyses ( PRISMA ) guidelines and study quality will be assessed by the Jadad score in addition to an evaluation of allocation concealment and data analysis . If sufficient data are available , a meta- analysis will be conducted . The effect sizes will be generated using Hedges ’ g score , for both fixed and r and om effect models . I2 statistics and Galbraith plots will be used to assess heterogeneity and identify their potential sources . Potential publication and small sample size bias will be assessed by visual inspections of funnel plots and also Egger 's test . Meta-regression analysis ( if feasible ) will be conducted with restricted maximum likelihood ( REML ) estimation method , controlling for potential confounders ( demographics , study methods , location , etc ) . A backward elimination process will be applied in the regression modelling procedure . Subgroup analysis , conditional on number of studies retrieved and their sample size , will be stratified on participant disease category , total dose administered , degree of 25(OH)D change and type of supplement used . Ethics and dissemination Formal ethical approval is not required as primary data will not be collected . The results will be disseminated through a peer- review ed publication , conference presentation and the popular press . Trial registration number International Prospect i ve Register for Systematic Review s ( PROSPERO ) number CRD42014013523
Available high- quality RCTs did not support a beneficial effect of cholecalciferol on systemic IL-6 and CRP .