Endocrine Society

Hypothyroidism ups the risk for small intestinal bacterial overgrowth

July 22, 2025

Small intestinal bacterial overgrowth (SIBO) was 2.2 times more likely in hypothyroid patients in this study, yet the risk appears to be mitigated in patients taking levothyroxine, according to research presented at the Endocrine Society's 2025 annual meeting.

Study details. Cedars-Sinai researchers analyzed small bowel fluid samples from adults, including 49 with hypothyroidism and 323 without, enrolled in the REIMAGINE study. All participants had undergone upper endoscopy without colon prep. DNA sequencing was used to identify microbial species in the gut.

Results. SIBO was significantly more prevalent in people with hypothyroidism (33%) vs. those without (15%). A separate review of medical records from the TriNetX database showed that people with hypothyroidism had a 2.2-fold increased risk of developing SIBO than matched controls, and those with autoimmune thyroiditis had a 2.4-fold increased risk. These risks were reduced in patients taking levothyroxine.

Source:

(2025, July 12). Endocrine Society. Thyroid treatment may improve gut health in people with hypothyroidism [Press release]. https://www.endocrine.org/news-and-advocacy/news-room/endo-annual-meeting/endo-2025-press-releases/mathur-press-release