Inflammatory Bowel Disease and Risk of Rheumatoid Arthritis: A UK Biobank Cohort Study

Inflammatory bowel disease (IBD) and rheumatoid arthritis (RA) are both prevalent inflammatory conditions within the population. Our objective was to explore the relationship between IBD and RA, while examining the role of inflammatory mediators in the observed association.

We used data from the UK Biobank, a population-based prospective cohort study that recruited adults aged 37-73 years from 22 centers in England, Scotland, and Wales between 2006 and 2010. We included patients diagnosed with IBD at baseline and excluded those with RA at baseline or missing follow-up information. Cox regression proportional hazard models were employed to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) between patients with IBD (Ulcerative colitis and Crohn's disease) at baseline and the risk of RA. Additionally, we conducted mediation analysis to examine the roles of C-reactive protein (CRP) and several composite inflammatory indices as potential mediators.

After excluding participants with RA at baseline (N = 6769), those lacking IBD subtype information (N = 475), and those with missing covariate data (N = 121 195), a total of 373 693 individuals were included in the analysis. Compared with individuals without IBD, those with IBD had a significantly higher risk of developing RA (hazard ratio 2.06, 95% confidence interval 1.69-2.51). This association remained robust after adjustment for multiple confounders and across all major subgroups. Notably, the risk of RA associated with IBD was even higher among individuals with a low polygenic risk score for RA. Mediation analysis showed that systemic inflammatory markers, such as CRP, explained only a modest proportion of the association between IBD and RA, with the highest mediation proportion observed being 9.56%.

In the UK Biobank cohort study, individuals with IBD demonstrated an increased risk of developing RA. Future research should aim to gain insight into these underlying mechanisms and explore ways to improve long-term health outcomes in these patients.