Immune-mediated diseases and risk of Crohn's disease or ulcerative colitis: a prospective cohort study

Background Although immune-mediated diseases (IMDs) including inflammatory bowel diseases (IBDs) are known to cluster, to what extent this is due to common environmental influences is unknown. Aim To examine the incidence of IBD in individuals with another IMD. Methods We used data from the prospective Nurses' Health Study II cohort (1995-2017) to examine the effect of diagnoses of several common IMDs on subsequent risk of Crohn's disease (CD) or ulcerative colitis (UC) using Cox proportional hazards models, adjusting for detailed diet and lifestyle confounders. Results We documented 132 cases of CD and 186 cases of UC over 2 016 163 person-years of follow-up (median age at IBD diagnosis 50 years). Compared to participants with no history of IMD, the HRs of CD for those with 1 and >= 2 IMDs were 2.57 (95% CI 1.77-3.74) and 2.74 (95% CI 1.36 to 5.49), respectively (P-trend < 0.0001). This association was only modestly attenuated by adjustment for environmental risk factors (HR 2.35 and 2.46, respectively). The risk of UC was not increased, with multivariable-adjusted HRs of 1.22 (95% CI 0.85-1.76) and 1.33 (95% CI 0.67-2.65) for those with 1 and >= 2 IMDs, respectively, compared to those with none (P-trend 0.16) (P-heterogeneity comparing CD and UC 0.037). Asthma, atopic dermatitis, psoriasis and rosacea were individually associated with higher risk of CD (HR ranging from 2.15 to 3.39) but not UC. Conclusions Individuals with one or more IMDs are at an increased risk for CD but not UC.