Environmental factors in inflammatory bowel disease: A case-control study based on a Danish inception cohort

Background: The role of environmental factors in development of inflammatory bowel disease (IBD) remains uncertain. The aim of the present study was to assess a number of formerly suggested environmental factors in a case-control study of an unselected and recently diagnosed group of patients with IBD and a control group of orthopaedic patients. Methods: A total of 123 patients diagnosed with Crohn's disease (CD) and 144 with ulcerative colitis (UC) in Copenhagen (2003–2004) were matched 1:1 on age and gender to 267 orthopaedic controls. Participants received a questionnaire with 87 questions concerning environmental factors prior to IBD/orthopaedic admission. Odds ratios (OR) were calculated by logistic regression. Results: Being breastfed > 6 months (OR, 0.50; 95% CI, 0.23–1.11) and undergoing tonsillectomy (OR, 0.49; 95% CI, 0.31–0.78) decreased the odds for IBD, whereas appendectomy decreased the odds for UC only (OR, 0.29; 95% CI, 0.12–0.71). Vaccination against pertussis (OR, 2.08; 95% CI, 1.07–4.03) and polio (OR, 2.38; 95% CI, 1.04–5.43) increased the odds for IBD, whereas measles infection increased the odds for UC (OR, 3.50; 95% CI, 1.15–10.6). Low consumption of fibres and high consumption of sugar were significantly associated with development of CD and UC. Smoking increased the risk for CD and protected against UC. Conclusion: Among Danish patients with CD and UC belonging to an unselected cohort, disease occurrence was found to be associated both with well-known factors such as smoking and appendectomy, and with more debated factors including breastfeeding, tonsillectomy, childhood vaccinations, childhood infections, and dietary intake of fibres and sugar. Highlights: ► The aetiology of inflammatory bowel diseases remains uncertain. ► Smoking was positively associated with CD and negatively associated with UC. ► Low consumption of dietary fibres and high consumption of sugar increased the risk for IBD. ► Appendectomy decreased the risk for UC. Tonsillectomy decreased the risk for both UC and CD. ► Childhood infections and vaccinations may also play an aetiological role in IBD.