Introduction An interrelation between chronic lower respiratory diseases (CLD) and inflammatory bowel disease (IBD) has previous been reported. The topic has mostly been addressed from the perspective of airway disease occurring as an extraintestinal manifestation after IBD-onset.

Aim The aim of the present study was to investigate risk of CLD before the development of IBD.

Methods The study period was from 1999 to 2018. The IBD-cohort was defined based on registrations in the Danish National Patient Registry (International Classification of Diseases, 10th revision (ICD-10) CD; K50, UC; K51) between 2003 and 2013. IBD cases were matched 1:10 with non-IBD individuals (controls). Patients with CLD were identified in a four-year period prior to the IBD diagnosis/index date using the ICD-10 diagnostic codes in the Danish National Patient registry (J40-J44, J45 and J47) as well as ATC codes from the Danish National Prescription Registry (RO3X). Both incident and prevalent cases of CLD were included. Logistic regression was used to estimate the odds ratio.

Results 24,238 IBD cases and 242,380 controls were identified. According to our case definitions, 2,785 (11.5%) IBD cases and 18,318 (7.6%) in the control group had CLD. Estimated odds ratio (OR) 1.60 (95% CI: 1.53-1.67). The estimated ORs (95% CI) for the IBD subtypes ulcerative colitis and Crohn?s disease were 1.53 (1.45-1.61) and 1.77 (1.65-1.981), respectively.

Conclusion We observed increased odds of CLD among persons who later developed IBD compared to those who did not.