title: Serum 25(OH)D response to vitamin D3 supplementation: a meta-regression analysis.
abstract: OBJECTIVE
  The aim of this study was to review factors that influence serum 25(OH)D when patients are given vitamin D supplements.
  
  
  METHODS
  From a comprehensive search of all randomized controlled clinical trials with vitamin D3 supplementation available on PubMed up to November 2011, we selected 33 with 43 treatment arms that included at least 30 adult participants. The achieved pooled mean difference (PMD) and 95% confidence intervals (CIs) were calculated using the random-effects models. Meta-regression and subgroup analyses were performed for prespecified factors, including dose, duration, baseline serum 25(OH)D, and age.
  
  
  RESULTS
  With a mean baseline serum 25(OH)D of 50.4 nmol/L, PMD was 37 nmol/L (95% CI, 33-41) with significant heterogeneity among studies. Dose (slope: 0.006; P < 0.001), trial duration (slope: 0.21; P < 0.001), baseline serum 25(OH)D (slope: -0.19; P < 0.001), and age (slope: 0.42; P < 0.001) independently influenced vitamin D response. Similar results were found in studies with a mean baseline serum 25(OH)D <50 nmol/L. In subgroup analyses, the PMD was higher with doses ≥800 IU/d (39.3 nmol/L) after 6 to 12 mo (41.7 nmol/L), with baseline 25(OH)D <50 nmol/L (39.6 nmol/L), and in adults aged >80 y (40.5 nmol/L).
  
  
  CONCLUSIONS
  This meta regression indicates that a higher increase in serum levels of 25(OH)D in adults is found with a dose of ≥800 IU/d, after at least 6 to 12 mo, and even when baseline 25(OH)D is low and in adults >80 y.
authors.affiliation: Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran. Electronic address: s_shabbidar@tums.ac.ir.
authors.forename: Sakineh
authors.initials: S
authors.lastname: Shab-Bidar
authors.affiliation: Department of Internal Medicine, Subdivision Rheumatology, Maastricht University Medical Centre, Maastricht, The Netherlands.
authors.forename: Sandrine
authors.initials: S
authors.lastname: Bours
authors.affiliation: Department of Internal Medicine, Subdivision Rheumatology, Maastricht University Medical Centre, Maastricht, The Netherlands; Biomedical Research Center, University Hasselt, Hasselt, Belgium; CAPHRI, Maastricht University, Maastricht, The Netherlands.
authors.forename: Piet P M M
authors.initials: PP
authors.lastname: Geusens
authors.affiliation: Department of Epidemiology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Alfons G H
authors.initials: AG
authors.lastname: Kessels
authors.affiliation: Department of Internal Medicine, Subdivision Rheumatology, Maastricht University Medical Centre, Maastricht, The Netherlands; Biomedical Research Center, University Hasselt, Hasselt, Belgium; VieCuri MC Noord Limburg, Venlo, The Netherlands; Nutrim School for Nutrition, Toxicology and Metabolism, Maastricht, The Netherlands.
authors.forename: Joop P W
authors.initials: JP
authors.lastname: van den Bergh
mesh_terms: D002762:Cholecalciferol / Q000008:administration & dosage* / Q000494:pharmacology; D019587:Dietary Supplements; D006801:Humans; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000097:blood / Q000494:pharmacology; D014808:Vitamin D Deficiency / Q000097:blood / Q000188:drug therapy*
chemical_list: D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D
keywords: Meta-regression; Serum 25(OH)D; Supplementation; Vitamin D(3)