Early life exposures and risk of inflammatory bowel disease: A nested case-control study in Quebec, Canada.

Background: Early life factors for inflammatory bowel disease are likely to impact the gut microbiota.

Aim: We investigated the associations between early exposures and inflammatory bowel disease.

Methods: This case-control study was nested within the CO·MMUNITY cohort. Cases of Crohn's disease (CD) and ulcerative colitis (UC) were identified using validated algorithms. All cases and randomly selected controls were invited to complete a questionnaire including early life exposures. Analyses were conducted by logistic regression and causal mediation (direct/indirect effects for passive/active smoking).

Results: Early introduction of solid foods at 3-6 months tended to increase CD risk compared to later introduction (>6 months): OR = 1.23; 95 % CI: 0.96-1.56, but not of UC. Exclusive breastfeeding tended to decrease the risk of CD (OR = 0.77; 95 % CI: 0.55-1.08), less so for UC. Antibiotics tended to decrease CD (OR = 0.89; 95 % CI: 0.74-1.07) and UC (OR = 0.88; 95 % CI: 0.71-1.09). No association was found between pets and CD or UC. Passive smoking increased CD risk (OR = 1.23; 95 % CI: 1.00-1.51), 20 % of which was mediated by active smoking, but not UC.

Conclusion: Differences were noticed in early risk factors for CD and UC. The impact of passive smoking was largely independent of active smoking, highlighting its importance for prevention.