Long-term risk of inflammatory bowel disease in patients with irritable bowel syndrome: the cross-sectional and longitudinal relationship.

Background: Irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) are distinct gastrointestinal disorders with overlapping symptoms and pathophysiological background. The long-term risk of IBD is unclear in IBS patients.

Methods: Overall, 447,631 participants free of IBD at baseline (2006-2010) and 76,992 individuals who completed Digestive Health Questionnaire (2017-2018) from UK Biobank were enrolled in longitudinal cohort and cross-sectional analysis, respectively. The primary outcome was incident IBD in the cohort design, and Cox proportional hazards model was conducted to estimate the associated hazard ratio (HR). Prevalent IBD was defined as primary outcome in the cross-sectional design, and logistic regression was performed to estimate the associated odds ratio (OR).

Results: In the cohort design, 2,916 incident IBD cases were identified during a median 14.2 years' follow-up, with 2,097 ulcerative colitis (UC) and 1,015 Crohn's disease (CD), respectively. IBS patients had a 68%, 60%, and 104% increased risk of IBD (HR = 1.68, 95% CI:1.47-1.92), UC (HR = 1.60, 1.36-1.89), and CD (HR = 2.04, 1.66-2.51) versus non-IBS participants. Moreover, a greater risk of incident IBD persisted in IBS patients even after 10 years' duration (HR = 1.55, 1.27-1.89). In cross-sectional analysis, IBS patients exhibited significantly elevated odds of IBD (OR = 2.40, 2.14-2.70), UC (OR = 2.18, 1.92-2.48), and CD (OR = 3.15, 2.68-3.70). A greater odds of IBD was observed among all IBS subtypes, with IBS-D showing the highest odds (OR = 3.72, 3.24-4.28).

Conclusions: The risk of incident IBD, either UC or CD, is significantly higher in IBS patients compared with the general population, especially in IBS-D patients.