Small Intestinal Bacterial Overgrowth (SIBO) Can be Caused by an Underactive Thyroid

Although we think of Small Intestinal Bacterial Overgrowth (SIBO) as being predominantly an infection, this fascinating study shows that over 50% of those with a low thyroid have SIBO as well (vs. 5% of those with normal thyroid function).

In the November 2007 issue of the Journal of Clinical Endocrinology and Metabolism, Dr. Antonio Gasbarrini of the Catholic University of the Scared Heart, Rome and colleagues note that thyroid hormones may influence gut motility, and hence the likelihood of SIBO. To investigate further, the researchers studied 50 patients with a history of overt hypothyroidism due to Hashimoto's (autoimmune) thyroiditis, and 40 controls.

A hydrogen glucose breath (HBT) test indicated SIBO in 27 of the patients (54%) versus 2 (5%) of the controls who had a normal thyroid. Symptoms such as abdominal discomfort, flatulence and bloating were significantly more prevalent in the SIBO group. After prescribing these patients 400 mg of Rifaximin 3x a day for a week, there was a significant improvement in the symptoms.

On a reassuring note, antibiotic therapy did not significantly change thyroid hormone plasma levels, indicating, say the investigators, that “carbohydrate fermenting bacteria do not interfere with thyroid hormone levels.”

J Clin Endocrinol Metab 2007;92:4180-4184.

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Also see "Small Intestinal Bacterial Overgrowth (SIBO)—An Easily Addressable Cause of Spastic Colon and Bowel Symptoms in CFS and Fibromyalgia.”