Background: The aetiology of inflammatory bowel disease (IBD) is not known but is likely to involve a combination of genetic predisposition and environmental risk factors. Smoking has been associated consistently with a higher risk of Crohn's disease (CD), while appendectomy and smoking appear to diminish the risk of ulcerative colitis (UC). The roles of other environmental factors are unclear. The aim of the present study was to evaluate the association of CD and UC with several environmental risk factors.
Methods: This case-control study included 338 patients (190 CD, 148 UC) and 355 controls. All subjects completed a detailed questionnaire regarding breastfeeding duration, history of helminthic infections, allergic diseases, appendectomy, household size, housing type, contact with specific domestic animals, physical activity, and smoking. Associations between risk factors and CD and UC were investigated by univariate and multivariate analysis.
Results: On multivariate analysis, CD associated with smoking at diagnosis (odds ratio, OR, 3.7, 95% CI 2.2-6.2; p < 0.001), being breastfed for <6 months (OR 2.7, 95% CI 1.7-4.4; p < 0.001), and less than two childhood sporting activities weekly (OR 2.7, 95% CI 1.5-5.0; p < 0.001) and inversely associated with frequent contact with cats in childhood (OR 0.6, 95% CI 0.4-0.9; p < 0.03). UC associated with less than two sporting weekly activities in childhood (OR 2.0, 95% CI 1.1-3.5, p = 0.02), fewer household members in childhood (OR 0.8, 95% CI 0.7-0.98, p = 0.03), and being breastfed for <6 months (OR 1.7, 95% CI 1.02-2.8, p = 0.04). A composite environmental risk index for CD revealed that 47 and 14% of the controls and patients with CD had no risk factors, respectively, and that 14 and 38% of the controls and patients with CD had at least two risk factors, respectively.
Conclusion: CD and UC associated with infrequent childhood sports activities and short breastfeeding. Furthermore, CD associated with smoking and infrequent contact with animals in childhood. UC associated with a smaller family size in childhood.
Keywords: Crohn’s disease; breastfeeding; case-control study; contact with animals; enviromental risk factors; etiology; inflammatory bowel disease; physical activity; smoking; ulcerative colitis.