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

Quick Summary

This study examined whether people with hypothyroidism (underactive thyroid) have higher rates of SIBO and different bacteria in their small intestine. Researchers found that hypothyroid patients were 2.2 times more likely to develop SIBO over 10 years, but taking levothyroxine (thyroid replacement medication) appeared to reduce this risk. The bacterial makeup in the small intestine differed between hypothyroid and non-hypothyroid patients, particularly in which types of Gram-negative bacteria were present.

What Was Studied

Researchers investigated whether hypothyroidism increases the risk of developing SIBO and whether it changes the types of bacteria in the small intestine. The study analyzed duodenal (upper small intestine) samples from 49 people with hypothyroidism and 323 controls, and separately analyzed 10-year SIBO development rates in large patient databases.

How the Study Was Conducted

This study combined two approaches: analyzing small intestine fluid samples from the REIMAGINE study using DNA sequencing to identify bacteria, and using the TriNetX database to track SIBO diagnosis rates over 10 years in hypothyroid patients compared to matched control groups. Researchers compared bacterial populations between four groups: hypothyroid with SIBO, hypothyroid without SIBO, non-hypothyroid with SIBO, and non-hypothyroid without SIBO. Full methodology not publicly available — summary based on abstract only.

Key Findings

• SIBO was more than twice as common in hypothyroid patients (32.65%) compared to controls (15.17%), with hypothyroid patients showing 2.20 times higher risk and autoimmune thyroiditis patients showing 2.40 times higher risk of developing SIBO over 10 years
• Taking levothyroxine (thyroid replacement medication) appeared to reduce SIBO risk, lowering it to 0.33 times normal in general hypothyroid patients and 0.78 times normal in autoimmune thyroiditis patients
• The types of bacteria differed between groups: Neisseria bacteria were core members only in hypothyroid patients, while Escherichia/Shigella dominated in non-hypothyroid SIBO patients and Klebsiella species were more common in hypothyroid SIBO patients
• Both SIBO groups showed increased Gram-negative coliforms (a family of bacteria including E. coli), but the specific types differed based on thyroid status