Association between hypothyroidism and small intestinal bacterial overgrowth

Area of Science:

• Endocrinology
• Gastroenterology
• Microbiology

Background:

• Hypothyroidism can cause intestinal dysmotility, potentially leading to small intestinal bacterial overgrowth (SIBO).
• SIBO may influence gastrointestinal symptoms and levothyroxine absorption in hypothyroid patients.

Purpose of the Study:

• To determine the prevalence of SIBO in patients with a history of overt hypothyroidism.
• To investigate the clinical presentation of SIBO in this population.
• To evaluate the impact of SIBO decontamination on thyroid hormone levels.

Main Methods:

• 50 patients with autoimmune thyroiditis and overt hypothyroidism were enrolled.
• SIBO diagnosis was confirmed via hydrogen glucose breath test.
• Positive patients received a 7-day course of rifaximin, with reassessment of breath tests, symptoms, and thyroid hormones after 1 month.

Main Results:

• 54% of hypothyroid patients had SIBO, significantly higher than controls (5%).
• SIBO-positive patients reported more abdominal discomfort, flatulence, and bloating, which improved post-treatment.
• Successful SIBO decontamination did not significantly alter thyroid hormone plasma levels.

Conclusions:

• Overt hypothyroidism is linked to an increased risk of developing SIBO.
• SIBO significantly contributes to gastrointestinal symptoms in hypothyroid individuals.
• Antibiotic treatment for SIBO effectively alleviates gastrointestinal symptoms without impacting thyroid hormone levels.