Psoriasis as a Potential Risk Factor for Inflammatory Bowel Disease: Findings from a Nationally Representative Korean Population.

Background/Objectives: Psoriasis is a chronic immune-mediated disorder that may share pathogenic pathways with inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD). Although Western studies suggest a possible link between psoriasis and increased IBD risk, large-scale evidence from Asian populations remains limited and inconsistent. Using nationwide Korean cohort data, we aimed to investigate this association. Methods: In this retrospective, nested case-control study using the Korean National Health Insurance Service-National Sample Cohort (2002-2019), incident IBD cases were matched 1:4 to controls by age, sex, income, region, and index date. Psoriasis history prior to the IBD index date was identified using diagnostic codes. Overlap propensity score weighting balanced covariates, and weighted multivariable logistic regression estimated adjusted odds ratios (aORs) with 95% confidence intervals (CIs). Results: Among 10,966 IBD patients and 43,864 controls, psoriasis was associated with higher IBD risk (aOR 1.63; 95% CI, 1.38-1.93). The association was stronger for UC (aOR 1.77; 95% CI, 1.44-2.18) than for CD (aOR 1.37; 95% CI, 1.01-1.84). UC risk was elevated across most subgroups, whereas CD risk reached significance only in individuals < 45 years. Conclusions: In this large, nationally representative Korean cohort, psoriasis was linked to an increased risk of subsequent IBD, particularly UC. Although causality cannot be inferred, these findings may underscore the importance of considering possible gastrointestinal comorbidity in patients with psoriasis.