Inflammatory Bowel Diseases Are Not Associated with an Increased Risk of Autoimmune Thyroiditis

Background/Objectives: The incidence of inflammatory bowel disease (IBD) is rising worldwide, particularly in Asia, while the highest prevalence remains in North America and Europe. Evidence on the relationship between IBD and the development of autoimmune thyroiditis is limited. This study investigated the association between IBD and a subsequent autoimmune thyroiditis in a large German primary care cohort over a 10-year period. Methods: Patients with IBD were propensity score matched to non-IBD individuals in a 1:5 ratio based on age, sex, index year, and average annual number of physician visits during follow-up. A total of 20,084 IBD patients-including 8791 with Crohn's disease and 11,293 with ulcerative colitis-and 100,420 matched controls were included. The primary outcome was the cumulative incidence of autoimmune thyroiditis, including Hashimoto's thyroiditis and Graves' disease. The association between IBD and autoimmune thyroiditis was evaluated using univariable conditional Cox regression analysis. Results: In the overall cohort, no significant association was found between IBD (Crohn's disease or ulcerative colitis) and autoimmune thyroiditis (Hashimoto's or Graves' disease). However, among patients aged ≥ 65 years, IBD was associated with a significantly increased risk of Graves' disease (HR 2.83; 95% CI 1.56-5.15), an effect observed in both Crohn's disease (HR 3.23; 95% CI 1.20-8.69) and ulcerative colitis (HR 2.64; 95% CI 1.25-5.60). Conclusions: While IBD was not associated with autoimmune thyroiditis overall, a significant positive association with Graves' disease was observed among patients aged ≥ 65 years, highlighting the importance of age-specific risk assessment.