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San Francisco, July 14, 2025 — New research presented at the Endocrine Society’s annual meeting (ENDO 2025) reveals that individuals with an underactive thyroid, or hypothyroidism, are at a significantly increased risk of developing small intestinal bacterial overgrowth (SIBO). The findings also indicate that this risk may be reduced with appropriate thyroid hormone treatment.
The study, led by Dr. Ruchi Mathur of Cedars-Sinai in Los Angeles, analyzed small bowel fluid samples from adults with and without hypothyroidism. Using DNA sequencing, researchers compared 49 people diagnosed with hypothyroidism to 323 controls. Results showed that 33% of those with hypothyroidism had SIBO, compared to just 15% of those without the condition.
The risk was even greater among those with autoimmune thyroiditis, a common cause of hypothyroidism. Dr. Mathur explained, “We now know that people with hypothyroidism, especially those with autoimmune thyroiditis, are more likely to develop SIBO, but this risk appears to be mitigated in those taking thyroid medications”.
Further analysis of medical records from a large database confirmed these findings, showing that people with hypothyroidism were 2.2 times more likely to develop SIBO than matched controls, and those with autoimmune thyroiditis had a 2.4 times higher risk. Importantly, the increased risk was less pronounced in patients taking levothyroxine, a common thyroid hormone replacement therapy.
The study also found distinct patterns of gut bacteria depending on thyroid status and the presence of SIBO, suggesting a possible microbiological mechanism linking the two conditions. Dr. Mathur noted that this could pave the way for more personalized treatments in the future.
“These findings open the door to new screening and prevention strategies. For example, doctors may begin to monitor thyroid health more closely in patients with SIBO, and vice versa,” Dr. Mathur said. She added that improving gut health could have far-reaching effects, potentially even helping to prevent autoimmune diseases such as Hashimoto’s thyroiditis.
Disclaimer:
This article is based on preliminary research presented at a scientific meeting and has not yet undergone peer review. The findings should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with any questions regarding a medical condition or treatment.
