Cedars-Sinai Study Links Hypothyroidism to GI Disorder
Findings Highlight Growing Understanding of How Gut Bacteria May Influence Disease Beyond the Digestive Tract
Patients with hypothyroidism—an underactive thyroid gland—may face significant risk of developing small intestinal bacterial overgrowth (SIBO), according to research led by Cedars-Sinai Health Sciences University investigators. SIBO can cause bloating, abdominal discomfort and changes in bowel habits.
The study, published in the Journal of Clinical Endocrinology & Metabolism, found that patients with hypothyroidism had more than double the risk of developing SIBO compared to those with normal thyroid function. The risk was even higher in patients with autoimmune thyroid disease, where the body’s immune system attacks the thyroid gland, but appeared lower in those receiving hormone treatment for the condition.
The findings offer insight into how specific changes in gut bacteria could contribute to disease beyond the gastrointestinal system.
“Studies like this remind us how interconnected the body’s systems are and the important role the microbiome plays in overall health,” said endocrinologist Ruchi Mathur, MD, director of Clinical Research and Clinical Operations for the Medically Associated Science and Technology (MAST) program and the study’s corresponding author.
Mathur sat down with the Cedars-Sinai Newsroom to share key takeaways from the investigation.
What did the study reveal about gut bacteria activity in patients with thyroid disease?
We found that patients with hypothyroidism had different patterns of bacteria in the small intestine compared with those without thyroid disease. In patients with both hypothyroidism and SIBO, we found Klebsiella bacteria dominated rather than the bacterial groups we more commonly see in SIBO. This suggests hypothyroidism may not only increase the risk of SIBO but may also influence the types of bacteria involved.
Could this mean a more severe form of SIBO?
Possibly, more research is needed to confirm this. Previous Cedars-Sinai research has shown that Klebsiella can disrupt the balance and interaction of bacteria in the small intestine more than some other bacterial groups.
How does thyroid hormone treatment affect SIBO risk?
One of the more interesting findings of our study was that patients receiving levothyroxine to treat their thyroid condition appeared to have a lower risk of developing SIBO compared with untreated patients. It is possible that thyroid hormone replacement affects gut motility, which may help reduce bacterial overgrowth in the small intestine. More research is needed, but the finding suggests thyroid treatment may influence digestive health in ways we are only beginning to understand.
Why is it important to study the small intestine directly?
Many microbiome studies rely on stool samples, but the bacteria found in stool can differ significantly from those living in the small intestine. The small intestine plays a central role in digestion, metabolism and hormone function, so studying it directly gives us a much more accurate picture of what may be happening in diseases such as hypothyroidism and SIBO. It also may help researchers identify future therapeutic targets.
What can physicians and patients learn from these new insights?
It is important to recognize the relationship between hypothyroidism and SIBO and address symptoms accordingly. If a patient with hypothyroidism is complaining of gastrointestinal symptoms such as bloating or altered bowel habits, their care team should consider evaluating them for SIBO. Likewise, if a patient presents with bloating, constipation or unexplained gastrointestinal symptoms, thyroid testing may also be appropriate.
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