Hypothyroidism and Risk of Inflammatory Bowel Disease: Influence of Age and Race in a Global Cohort.

BACKGROUND: Thyroid and gastrointestinal autoimmune conditions may share overlapping immunological, genetic, and microbial pathways, but the relationship between hypothyroidism and inflammatory bowel disease (IBD) remains unclear. METHODS: We conducted a retrospective cohort study using electronic health record data from 125 healthcare organizations within a global research network to examine the association between hypothyroidism and IBD in a large, racially diverse, multinational population, stratified by age and race. Adults aged 18 to 100 years with or without hypothyroidism were included. Those with IBD risk factors or prior diagnoses were excluded. The primary outcome was a new diagnosis of Crohn's disease or ulcerative colitis within five years after the hypothyroidism or control index date. Propensity score matching was performed 1:1 based on age and sex. Odds ratios were calculated to assess the association, stratified by race and age. RESULTS: Among nearly 30 million individuals, patients with hypothyroidism had a significantly increased risk of developing IBD in African American and Asian populations, with odds ratios of 1.329 and 1.662, respectively. In Caucasians, risk increased only in individuals over age 50, while those under 50 showed a slight reduction. The strength and direction of association varied by age and race. CONCLUSIONS: Hypothyroidism is associated with increased IBD risk primarily among older adults in African American, Asian, and Caucasian populations, while younger Caucasians showed a modest reduction in risk. These findings suggest a complex autoimmune relationship influenced by both age and race.