title: Vitamin D status in relation to Crohn's disease: Meta-analysis of observational studies.
abstract: OBJECTIVE
  Inconsistent findings have been published regarding vitamin D status among patients with Crohn's disease (CD) and the association with disease severity. We aimed to perform a meta-analysis evaluating serum 25-hydroxy vitamin D and 1,25 dehydroxyvitamin D among CD patients compared with healthy and non-healthy controls, the prevalence of vitamin D deficiency, and the association with disease.
  
  
  METHODS
  We searched MEDLINE, SCOPUS, EMBASE, and Google Scholar up to March 2015 for observational studies assessing serum vitamin D levels in CD patients. A total of 63 studies were included in the following four meta-analyses: 1) a meta-analysis on the mean difference of 25(OH)D levels in CD patients compared with healthy (number of studies = 27) and non-healthy (n = 25) controls; 2) a meta-analysis on the mean difference of 1,25(OH)2 D3 levels in CD patients compared with healthy (n = 7) and non-healthy (n = 8) controls; 3) a meta-analysis on the prevalence of vitamin D deficiency (n = 34); 4) a meta-analysis on the correlation coefficients between vitamin D status severity of CD (n = 6). Subgroup analysis and meta-regression were used to discover possible sources of between-study heterogeneity.
  
  
  RESULTS
  It was found that CD patients had lower levels of 25(OH)D compared with healthy (-3.99 ng/mL; 95% confidence interval [CI]: -5.91 to -2.08) but not non-healthy controls (-1.07 ng/mL; 95% CI: -2.84 to 0.70). There was also no significant mean difference for 1,25(OH)2 D3 for both healthy and non-healthy controls. Meta-analysis on the prevalence of vitamin D deficiency showed an overall prevalence of 57.7% (95% CI: 0.502-0.649). An inverse association was observed between serum vitamin D and severity of CD (-0.36; 95% CI: -0.48 to -0.24). Meta-regression showed that mean levels of 25(OH)D were decreased 0.09 for each unit change of latitude among CD patients compared with healthy controls (B = -0.09, P = 0.004, I(2) residual = 86.08%).
  
  
  CONCLUSIONS
  We found that patients with Crohn's disease had lower serum 25(OH)D concentrations compared with their healthy counterparts, and more than half of them have hypovitaminosis D. Moreover, there was an inverse correlation between circulating 25(OH)D concentrations and severity of Crohn's disease.
authors.affiliation: Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran; Students' Research Committee, Isfahan University of Medical Sciences, Isfahan, Iran; Department of Community Nutrition, School of Nutrition and Food Science, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Sadeghian
authors.affiliation: Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran; Students' Research Committee, Isfahan University of Medical Sciences, Isfahan, Iran; Department of Community Nutrition, School of Nutrition and Food Science, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Parvane
authors.initials: P
authors.lastname: Saneei
authors.affiliation: Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Fereydoun
authors.initials: F
authors.lastname: Siassi
authors.affiliation: Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran; Department of Community Nutrition, School of Nutrition and Food Science, Isfahan University of Medical Sciences, Isfahan, Iran; Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran. Electronic address: esmaillzadeh@hlth.mui.ac.ir.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Esmaillzadeh
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000097:blood; D000328:Adult; D002648:Child; D003424:Crohn Disease / Q000097:blood / Q000503:physiopathology*; D019317:Evidence-Based Medicine; D014943:Global Health; D006801:Humans; D009752:Nutritional Status; D064887:Observational Studies as Topic; D015995:Prevalence; D012720:Severity of Illness Index; D013472:Sunlight; D014808:Vitamin D Deficiency / Q000453:epidemiology / Q000209:etiology*
chemical_list: D015652:25-Hydroxyvitamin D 2
keywords: Crohn's disease; Deficiency; Disease activity; Meta-analysis; Vitamin D status