Risk of dementia in patients with inflammatory bowel disease: a Danish population‐based study

Background: Inflammatory bowel disease (IBD) may be associated with increased dementia risk, but the literature is conflicting. Aim: To investigate dementia risk in patients with IBD. Methods: We conducted a nationwide population-based cohort study in Denmark (1977–2018) including all patients with incident IBD matched with up to 10 general population comparators without IBD by sex, year of birth and region of residence. We calculated cumulative incidence proportions (CIPs) of dementia treating death as a competing risk, and adjusted hazard ratios (HRs) comparing IBD patients with matched comparisons. In a nested case–control analysis, we investigated the impact of IBD severity, steroid use, colorectal and small bowel surgery, and healthcare system contacts on dementia risk. Results: Of 88,985 patients with IBD (69.6% with ulcerative colitis [UC], 30.4% with Crohn's disease [CD]) and 884,108 comparisons, 2076 patients (78.1% with UC) and 23,011 comparisons (76.6% UC comparisons) developed dementia. The 40-year CIP of all-cause dementia was 7.2% for UC patients and 5.8% for CD patients. UC patients had a slightly increased HR of all-cause dementia (HR = 1.07 [95% confidence interval (CI): 1.01;1.12]) and Alzheimer's disease (HR = 1.10 [95% CI: 1.01–1.19]). CD patients had an increased HR of all-cause dementia (HR = 1.15 [95% CI: 1.05–1.27]) and frontotemporal dementia (HR = 2.70 [95% CI: 1.44–5.05]). Dementia in IBD patients was associated with frequent healthcare system contacts. Conclusions: UC and CD are associated with slightly increased all-cause dementia risk, particularly frontotemporal dementia in CD patients. Frequent healthcare system contacts by patients with IBD and detection bias may play a role in the association.