Risk of neurodegenerative diseases in patients with inflammatory bowel disease: a nationwide population-based cohort study.

Background and aims Although recent studies have reported that inflammatory bowel disease (IBD) is associated with the development of neurodegenerative diseases via chronic intestinal inflammation and the gut-brain axis, there is insufficient evidence supporting this notion. The aim of this study was to determine the risk of neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease (AD) in patients with IBD. Methods Using the National Health Insurance Service data for the entire Korean population, we identified patients with IBD and controls from 2009 to 2011 and followed them up until 2017. We selected the controls in a 1:4 ratio based on age and sex for comparison with cases. Results Of 24,830 IBD patients and 99,320 non-IBD controls, 98 IBD patients and 256 controls developed PD, while 644 IBD patients and 2,303 controls developed AD. The overall neurodegenerative disease risk was higher in IBD patients [PD: adjusted hazard ratio (HR), 1.56; 95% confidence interval (CI), 1.24-1.97; AD: adjusted HR, 1.14; 95% CI, 1.05-1.25). Younger IBD patients aged 40-65 years had a higher risk of PD compared to controls (adjusted HR, 2.34; 1.63-3.35)]. In contrast, patients aged ≥65 years had an increased risk of AD compared to controls (adjusted HR, 1.14; 1.04-1.25). In a nested case-control study of the IBD cohort, patients aged ≥65 years and the female sex were risk factors for AD, while living in an urban area was protective against AD. Conclusions The risk of neurodegenerative diseases was higher in IBD patients than in the non-IBD population.