Thyroid Therapy Could Enhance Gut Health in Hypothyroid Patients

Recent research reveals a significant link between hypothyroidism and small intestinal bacterial overgrowth (SIBO), a condition characterized by excessive bacteria in the small intestine. The study, presented at ENDO 2025 by the Endocrine Society in San Francisco, highlights that individuals with an underactive thyroid are at a higher risk of developing SIBO, but this risk appears to decrease with effective thyroid hormone treatment.

Dr. Ruchi Mathur, a leading endocrinologist at Cedars-Sinai, explained that patients with autoimmune thyroid disease, especially hypothyroidism, are more susceptible to SIBO. The research indicates that thyroid medication, such as levothyroxine, may help mitigate this risk. The underlying mechanism might involve alterations in the gut microbiome related to thyroid hormone levels.

The study involved analyzing small bowel fluid samples from 49 hypothyroid patients and 323 controls. DNA sequencing revealed that 33% of hypothyroid individuals had SIBO compared to 15% of controls. Researchers further examined bacterial patterns in four groups divided by thyroid health and SIBO status, finding that gut bacteria compositions differ depending on these factors.

Additionally, large-scale analysis using the TriNetX database showed that people with hypothyroidism or autoimmune thyroiditis face 2.2 to 2.4 times higher risk of developing SIBO compared to controls. Importantly, patients on levothyroxine had a reduced risk, emphasizing the potential benefits of thyroid hormone therapy.

These insights suggest that enhancing thyroid health can improve gut microbiota balance, potentially reducing SIBO incidence. The findings advocate for more integrated monitoring of thyroid function and gut health, offering the possibility of personalized treatment approaches that could also impact autoimmune disease prevention, including Hashimoto’s thyroiditis.

As research continues, a better understanding of the microbiological mechanisms involved could lead to targeted therapies, helping at-risk populations maintain both thyroid and gut health.