SUN-396 Small Intestinal Bacterial Overgrowth Associated With Higher Risk of Hashimoto’s Thyroiditis

Abstract Disclosure: S. Mehravar: None. M. Wei: None. G. Leite: None. G.M. Barlow: None. A. Rezaie: None. P. Naji: None. M. Pimentel: None. R. Mathur: None. Introduction: Small Intestinal Bacterial Overgrowth (SIBO) is characterized by an excessive proliferation of bacteria in the small intestine, leading to symptoms such as bloating, diarrhea, constipation, and nutrient malabsorption. This imbalance in gut microbiota can interfere with digestion, impair gut motility, and contribute to systemic inflammation. The causes of SIBO are multifactorial. Hashimoto’s thyroiditis (HT) is a chronic autoimmune disorder in which the immune system attacks the thyroid gland, resulting in inflammation and gradual thyroid destruction. This leads to hypothyroidism, characterized by insufficient thyroid hormone production. In this study, we aim to investigate the relationship between SIBO and HT, assessing whether SIBO increases the risk of developing HT or if there is a potential bidirectional interaction between gut dysbiosis and thyroid function. Methodology: This retrospective cohort study analyzed patient data from the TriNetX database, which includes de-identified medical records from over 130 million patients across 94 healthcare organizations in the United States. The study compared patients diagnosed with SIBO (ICD-10: K63.821) to those without SIBO on breath test, excluding individuals with pre-existing thyroid conditions such as thyroiditis, thyrotoxicosis, thyroidectomy, and hypothyroidism, as well as those with thyroid-stimulating hormone (TSH) levels more than 5 IU/L before the index event. Patients were monitored over a six-year period for the potential development of HT, as indicated by thyroid peroxidase (TPO) antibody levels exceeding 30 IU/L or diagnosis of thyroiditis. The study was conducted from January 1, 2019, to January 23, 2025. To ensure comparability, both cohorts were matched based on 49 characteristics, including demographics (age, sex, ethnicity, race), comorbidities, laboratory results, and medication history. Results: Before propensity score matching, the study included 6,951 patients with SIBO and 34,159 without SIBO. After matching, each group comprised 6,948 patients, with a mean age of 47.5 ± 18 years. Of the total participants, 69% were female. Racial distribution was as follows: 75% White, 6.7% Black or African American, and 3% Asian. Analysis revealed that the risk of developing HT was higher in the SIBO group (38 out of 6,929; 0.548%) compared to the non-SIBO group (15 out of 6,920; 0.217%). The calculated risk ratio (RR) was 2.53, with a 95% confidence interval (CI) of 1.39-4.96, suggesting a significant association between SIBO and the increased risk of autoimmune thyroid disease. Conclusion: This study highlights a potential link between SIBO and the development of Hashimoto’s thyroiditis, suggesting that patients with SIBO may be at a higher risk of thyroid autoimmunity. Further research is needed to explore the underlying mechanisms connecting gut dysbiosis and thyroid autoimmunity. Presentation: Sunday, July 13, 2025