Bidirectional associations between depression and inflammatory bowel disease in a nationwide Korean cohort.

Inflammatory bowel disease (IBD) and depression frequently co-occur, and previous studies have suggested temporal associations in both directions. We conducted two complementary matched cohort studies using the Korean National Health Insurance Service database to further characterize these associations in a nationwide Korean population. In Study I, 11,725 patients with ulcerative colitis (UC) and 2918 patients with Crohn's disease (CD) were matched with 58,572 controls without IBD to assess incident depression. In Study II, 622,131 individuals with depression were matched 1:1 with 622,131 controls without depression to assess incident UC and CD. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using stratified Cox proportional hazards models adjusted for demographic, lifestyle, metabolic, and clinical covariates. UC was associated with an increased risk of subsequent depression (adjusted HR, 1.24; 95% CI, 1.14-1.36), whereas CD was not significantly associated with depression (adjusted HR, 1.14; 95% CI, 0.93-1.39). Conversely, depression was associated with increased risks of subsequent UC (adjusted HR, 1.31; 95% CI, 1.14-1.52) and CD (adjusted HR, 1.62; 95% CI, 1.20-2.18). These findings provide complementary evidence of associations in both temporal directions between depression and IBD, although the pattern was not symmetric across IBD subtypes.