title: Association between 25(OH)D Level, Ultraviolet Exposure, Geographical Location, and Inflammatory Bowel Disease Activity: A Systematic Review and Meta-Analysis.
abstract: BACKGROUND
  There is no consensus on the vitamin D levels and inflammatory bowel disease (IBD).
  
  
  OBJECTIVE
  To conduct a systematic review and meta-analysis to analyze the relationship between IBD and 25(OH)D, sun exposure, and latitude, and to determine whether vitamin D deficiency affects the severity of IBD.
  
  
  METHODS
  We searched the PubMed, EBSCO, and ClinicalTrials.gov databases to identify all studies that assessed the association between 25(OH)D, sun exposure, latitude, and IBD through November 1, 2014, without language restrictions. Studies that compared 25(OH)D levels between IBD patients and controls were selected for inclusion in the meta-analysis. We calculated pooled standardized mean differences (SMDs) and odds ratios (ORs).
  
  
  RESULTS
  Thirteen case-control studies investigating CD and 25(OH)D levels were included, and eight studies part of above studies also investigated the relationship between UC and 25(OH)D. Both CD patients (SMD: 0.26 nmol/L, 95% confidence interval [CI]: 0.09-0.42 nmol/L) and UC patients (SMD: 0.5 nmol/L, 95% CI: 0.15-0.85 nmol/L) had lower levels of 25(OH)D than controls. In addition, CD patients and UC patients were 1.95 times (OR, 1.95; 95% CI, 1.48-2.57) and 2.02 times (OR, 2.02; 95% CI, 1.13-3.60) more likely to be 25(OH)D deficient than controls. We also included 10 studies investigating the relationship between CD activity and vitamin D. Results showed that patients with active CD (CD Activity Index ≥ 150) were more likely to have low vitamin D levels. In addition, whether low sun exposure and high latitude were related to a high morbidity of CD need to be provided more evidence.
  
  
  CONCLUSIONS
  Our study shows that IBD patients have lower vitamin D levels. For active CD patients, vitamin D levels were low. These findings suggest that vitamin D may play an important role in the development of IBD, although a direct association could not be determined in our study.
authors.affiliation: Department of Gastroenterology, the First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, 310003, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Lu
authors.affiliation: Department of Gastroenterology, the First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, 310003, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Gastroenterology, the First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, 310003, China.
authors.forename: Weilai
authors.initials: W
authors.lastname: Yu
authors.affiliation: Department of Gastroenterology, the First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, 310003, China.
authors.forename: Dejian
authors.initials: D
authors.lastname: Li
authors.affiliation: Department of Gastroenterology, the First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, 310003, China.
authors.forename: Zun
authors.initials: Z
authors.lastname: Xiang
authors.affiliation: Department of Gastroenterology, the First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, 310003, China.
authors.forename: Yiming
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Department of Gastroenterology, the First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, 310003, China.
authors.forename: Chaohui
authors.initials: C
authors.lastname: Yu
mesh_terms: D002112:Calcifediol / Q000378:metabolism*; D005843:Geography; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000453:epidemiology* / Q000378:metabolism*; D000069079:Radiation Exposure / Q000032:analysis*; D014466:Ultraviolet Rays
chemical_list: D002112:Calcifediol