Background: Data on the influence of rural/urban and coastal/inland environment on inflammatory bowel disease (IBD) are either conflicting or lacking. Our aim was to analyze whether the environment has any influence on the prevalence, phenotype, and course of IBD.
Materials and methods: We carried out a multicenter retrospective study in 1194 IBD patients from Galicia, Spain. Urban areas were defined as those with over 25,000 inhabitants. Sex, age, family history, smoking, Montreal classification, extraintestinal manifestations, steroid dependence/refractoriness, and treatment were assessed. We used the Student's t-test/Mann-Whitney U tests to compare continuous variables and χ to compare categorical variables. Logistic regression was also used.
Results: Living in urban municipalities was a risk factor for Crohn's disease [relative risk (RR) 1.47; 95% confidence interval (CI) 1.25-1.73; P<0.001]; living in coastal municipalities was a protective factor for ulcerative colitis (RR 0.71; 95% CI 0.60-0.85; P<0.001). Crohn's disease patients living on the coast had more frequent ileocolonic disease and needed immunosuppressives more frequently than inland patients (RR for inland 0.65; 95% CI 0.47-0.90; P=0.008). Urban Crohn's disease patients needed immunosuppressives more frequently than rural patients (RR 1.41; 95% CI 1.04-1.92; P=0.027). Urban ulcerative colitis patients had left-sided colitis less frequently. Coastal ulcerative colitis patients more frequently had extensive colitis.
Conclusion: Crohn's disease was found more frequently in urban and coastal areas and ulcerative colitis in inland municipalities. Place of residence may also influence phenotype and clinical course as patients living on the coast have more frequent ileocolonic Crohn's disease phenotype, extensive ulcerative colitis, and greater need for immunosuppressive therapy.