The relationship between urban environment and the inflammatory bowel diseases: a systematic review and meta-analysis (BMC Gastroenterology)

Background: The objective of this study was to conduct a systematic review with meta-analysis of studiesassessing the association between living in an urban environment and the development of theCrohn`s disease (CD) or ulcerative colitis (UC). Methods: A systematic literature search of MEDLINE (1950-Oct. 2009) and EMBASE (1980-Oct.2009) was conducted to identify studies investigating the relationship between urbanenvironment and IBD. Cohort and case-control studies were analyzed using incidence rateratio (IRR) or odds ratio (OR) with 95 % confidence intervals (CIs), respectively. Stratifiedand sensitivity analyses were performed to explore heterogeneity between studies and assesseffects of study quality. Results: The search strategy retrieved 6940 unique citations and 40 studies were selected forinclusion. Of these, 25 investigated the relationship between urban environment and UC and30 investigated this relationship with CD. Included in our analysis were 7 case-control UCstudies, 9 case-control CD studies, 18 cohort UC studies and 21 cohort CD studies. Based ona random effects model, the pooled IRRs for urban compared to rural environment for UCand CD studies were 1.17 (1.03, 1.32) and 1.42 (1.26, 1.60), respectively. These associationspersisted across multiple stratified and sensitivity analyses exploring clinical and studyquality factors. Heterogeneity was observed in the cohort studies for both UC and CD,whereas statistically significant heterogeneity was not observed for the case-control studies. Conclusions: A positive association between urban environment and both CD and UC was found.Heterogeneity may be explained by differences in study design and quality factors.