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The SIBO-Thyroid Connection
Reduced motility is one of the risk factors for development of a small intestinal bacterial overgrowth (SIBO). Hypothyroidism is associated with altered GI motility. (1)
Hypothyroidism is a common endocrine condition with inadequate production of thyroid hormone or suboptimal action of thyroid hormone on the target tissues. Hypothyroidism can either be primary or result of secondary causes.
Constipation is typical gastrointestinal (GI) symptoms of hypothyroidism.
Hypothyroidism also affects other systems. Systemic involvement affects the cardiovascular system, skin, neurological manifestations, menstrual disturbances in female etc., GI signs and symptoms may be seen due to disturbances in motility. Motor dysfunction results in altered motility and transit time. (1)
How Does Thyroid Effect The Gut?
Hypothyroidism prominently decreases the gastroesophageal motility and hence it is recommended to evaluate thyroid functions in admitted patients complaining dyspepsia. In order to evaluate whether there is any change in gastroesophageal motility due to hypothyroidism, some researchers studied 30 female patients with primary hypothyroidism with 10 healthy females as the control group. Motility disturbances in the form of significantly higher mean esophageal transit time and gastric emptying time were seen in patients with hypothyroidism compared with the control group (1).
The results proved that hypothyroidism reduces esophageal and gastric motor activity. Motility disturbances in hypothyroidism can lead to GI dysfunction. (1)
SIBO And Hypothyroidism
It has been reported that SIBO may be present in more than half of patients with hypothyroidism (1).
In one study of 90 subjects the researchers found that significantly higher numbers of patients (54%) with hypothyroidism have SIBO compared with the control group. (1)
Constipation is common in hypothyroid patients, but diarrhea is rarely reported. In one case study published, a young woman, who had been diagnosed with hypothyroidism, was struggling with chronic diarrhoea – in fact this was her main complaint.
There are two factors that strongly predict the presence of SIBO in people like this; positive hydrogen breath test and positive response to antibiotic.
In this example, both fasting hydrogen breath test was positive and antibiotic treatment was found to be successful. Bacterial overgrowth because of hypomotility may be the possible cause of diarrhoea in such patients. (1)
Slow GI motility in hypothyroidism may promote bacterial overgrowth leading to chronic GI symptoms.
SIBO is a common cause of chronic diarrhoea. In the literature, not many studies are found on the prevalence of SIBO in hypothyroidism, but the association of hypothyroidism and small bacterial overgrowth does exist. (1)
Hence, patients with chronic GI problems in hypothyroidism should be evaluated for SIBO.
Conclusions: The SIBO-Thyroid Connection
It is clear there is a very strong SIBO-thyroid connection. Gut motility is disturbed in hypothyroidism, which can lead to SIBO. SIBO may be responsible for chronic gut symptoms in these patients. It is important to evaluate the possibility of SIBO in patients with chronic gut symptoms with hypothyroidism.
- Link between hypothyroidism and small intestinal bacterial overgrowth (click here)
- Levothyroxine therapy and impaired clearance are the strongest contributors to small intestinal bacterial overgrowth: Results of a retrospective cohort study (click here)
- Levothyroxine Sodium Oral Solution Normalizes Thyroid Function in a Patient with Hashimoto’s Disease, Gastritis, Diabetic Gastroparesis, and Small Intestinal Bacterial Overgrowth (SIBO) (click here)
- Thyroid dysfunction in patients with small intestinal bacterial overgrowth (click here)
- Relation of Gut Microbes and L-Thyroxine Through Altered Thyroxine Metabolism in Subclinical Hypothyroidism Subjects (click here)