Relationship Between Hypothyroidism, Risk of Small Intestinal Bacterial Overgrowth, and Duodenal Microbiome Alterations

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Hypothyroidism is associated with a higher prevalence of small intestinal bacterial overgrowth (SIBO), with rates of 32.65% in hypothyroid subjects compared to 15.17% in controls.
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The 10-year cumulative incidence of SIBO is significantly higher in subjects with hypothyroidism (RR = 2.20) and autoimmune thyroiditis (RR = 2.40) compared to matched controls.
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Levothyroxine treatment appears to mitigate the risk of developing SIBO in hypothyroid patients, reducing relative risks to 0.33 and 0.78 for unspecified and autoimmune thyroiditis cases.
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The duodenal microbiome in hypothyroid subjects shows increased prevalence of specific Gram-negative coliforms, with Neisseria being part of the core microbiome in these individuals.
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Alterations in gut microbial populations may influence the development of both hypothyroidism and SIBO, highlighting the importance of studying the small bowel microbiome directly.

The Journal Of Clinical Endocrinology & Metabolism

by Margaret Wei, Sepideh Mehravar, Gabriela Leite, Parnian Naji, Gillian M Barlow, Ava Hosseini, Mohamad Rashid, Maritza Sanchez, Cristina M Fajardo, Mark Pimentel, Ruchi Mathur
September 5, 2025

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