Association between OLD and IBD: a systematic review and meta-analysis.

Objective: This study aimed to systematically evaluate the bidirectional association between obstructive lung diseases (OLD) [including chronic obstructive pulmonary disease (COPD), asthma, and bronchiectasis] and inflammatory bowel disease (IBD) [including Crohn's disease (CD) and ulcerative colitis (UC)]. Methods: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we conducted a systematic search of the PubMed, Embase, and Cochrane Library databases to identify relevant observational studies published up to 30 June 2025. The included studies were cohort studies, case-control studies, and cross-sectional studies that reported relative risk (RR), hazard ratio (HR), or odds ratio (OR) with 95% confidence intervals (CIs). Study quality was assessed using the Newcastle-Ottawa Scale (NOS), and data were analyzed using random effects or fixed effects models. HRs, RRs, and ORs were analyzed separately according to the direction of association and the disease subtype. Results: A total of 30 observational studies were included. In the estimate-stratified analyses, IBD was associated with an increased risk of subsequent COPD, while COPD was generally associated with increased risks of subsequent CD and UC, although the COPD-to-CD and COPD-to-UC analyses showed substantial heterogeneity. For bronchiectasis, available evidence suggested a positive association with IBD; however, the pooled estimate for IBD and subsequent bronchiectasis was imprecise and should be interpreted with caution. For asthma, the association was more consistent: IBD was associated with an increased risk of subsequent asthma in both HR- and OR-based analyses, and asthma was also associated with subsequent IBD in the HR-based analysis. The bidirectional association was generally stronger and more consistent for CD than for UC. Conclusion: This systematic review and meta-analysis supports positive associations between OLD and IBD, particularly for COPD with the IBD subtypes and for asthma with IBD, especially CD. These associations should be interpreted according to the OLD subtype and the age context. Clinicians should be attentive to respiratory comorbidities in patients with IBD, and appropriate respiratory symptom assessment or screening may help early identification and management. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, identifier CRD420251169706.