How SIBO and Thyroid Disease are Connected

Written by

Two of the most influential systems in the body are the thyroid and the gut. Both have far reaching effects and together impact areas such as immunity, cardiovascular function, neurological activity, energy level, and much more. The gut and thyroid share great interconnectivity meaning that dysfunction of one often leads to disruption of the other.

An excellent example of this is the association between small intestinal bacteria overgrowth (SIBO) and hypothyroidism. Even though these two conditions are seemingly unrelated they mutually affect the occurrence of one another. Because of their developmental relationship, it is important that individuals with SIBO or hypothyroidism have a strong understanding of both.

What is SIBO?

The gut is composed of multiple distinct sections all of which play an important role in digestion, immunity, and overall wellness – to learn even more about the gut, read this. These regions all contain their own ecosystems that include numerous microorganisms including bacteria. When compared to the other intestinal systems, the small intestine maintains a relatively low level of bacteria. However, in the case of SIBO, bacteria prevalence in the small intestine increases dramatically.

SIBO, or small intestinal bacteria overgrowth, is a relatively common but often underdiagnosed condition. This gastrointestinal issue is caused by excess growth or colonization of bacteria in the small intestine. An overabundance of bacteria such as that seen in SIBO can lead to many different gastrointestinal symptoms, nutrient deficiencies, and may even disrupt seemingly unrelated areas such as the brain, immune system, skin, heart, and thyroid.

Common symptoms of SIBO include gastrointestinal irregularities such as: nausea, bloating, diarrhea, constipation, and heartburn. The severity of SIBO symptoms range from mild to severe depending on individual patient factors.

What is Hypothyroidism?

The small butterfly-shaped gland known as the thyroid is a powerful regulator of wellness. Its influence is perhaps most apparent in areas such as immunity, energy level, weight regulation, and digestion. The thyroid exerts its influence through the use of various hormones.

Two of the most important hormones regarding thyroid function and overall health are T4, the storage form of thyroid hormone, and T3, the active form. In order to influence bodily processes, T4 must be converted into T3 and subsequently delivered to the appropriate cells and tissues.

Learn even more about the thyroid gland here.

Hypothyroidism is a common disorder that can cause a cascade of dysfunction throughout the body by inhibiting thyroid activity thereby slowing down numerous bodily processes. The condition may be caused by poor conversion, transport, receptivity, or production of thyroid hormones. A decline in thyroid activity can cause symptoms such as chronic fatigue, weight gain, difficulty thinking clearly, and poor digestion.

The Connection Between SIBO and Hypothyroidism

SIBO and hypothyroidism are frequently seen together. This is because both have a mutual degree of influence on the development and continuation of the other. In fact, experts estimate that nearly half of all thyroid patients suffer from some degree of bacterial overgrowth. Those with SIBO or hypothyroidism individually are at much greater risk of developing the other condition.

How Does SIBO Promote Hypothyroidism?

There are several ways in which SIBO may prompt the development of hypothyroidism. Studies show that SIBO is associated with factors of hypothyroidism including nutrient deficiencies, poor thyroid hormone conversion, and greater risk of autoimmune disease.

Nutrient absorption is one of the most important functions of the digestive tract. Those with SIBO often incur damage to the intestinal lining thereby inhibiting nutrient absorption. This leads to poor acquisition of essential vitamins, minerals, and nutrients such as zinc, tyrosine, selenium, vitamin A, and vitamin D that are necessary for healthy thyroid activity and hormone construction. Without resolving absorption issues and existing deficiencies it is unlikely that the thyroid will be able to maintain healthy hormone production.

The thyroid relies on healthy gut flora and appropriate bacterial balance to function properly. Approximately 20 percent of the inactive thyroid hormone (T4) is converted into the active form (T3) in the gut. If the gut is unable to facilitate this conversion, the likelihood of developing hypothyroid-like symptoms increases dramatically. Therefore, addressing intestinal issues such as SIBO is an important part of any thyroid treatment protocol.

SIBO also increases the risk of autoimmune disorders that can lead to major thyroid issues. Increased bacteria in the small intestine can contribute to a condition called leaky gut syndrome wherein particulates, toxins, and partially digested foods can escape into the bloodstream. This triggers an immune response that if left unresolved may develop into a more serious autoimmune disorder such as Hashimoto’s thyroiditis. Furthermore, studies suggest that SIBO patients tend to have higher levels of anti-thyroid peroxidase, which is an antibody highly associated with the development of Hashimoto’s and subsequent hypothyroidism.

How Does Hypothyroidism Contribute to SIBO?

As thyroid function slows and hormone levels decline, so too does activity throughout the body. One area frequently impacted by hypothyroidism is the digestive tract.

Reduced thyroid activity can cause the digestive tract to slow to a crawl, which allows bacteria to overtake areas such as the small intestine. Constipation, a common symptom of hypothyroidism, also contributes to increased bacteria growth in the intestine. Furthermore, poor thyroid function may impede the body’s migrating motility complex (MMC) responsible for moving contents of the digestive tract. Disruption of intestinal motility can contribute greatly to the development of SIBO.

Stomach acid is an important part of the digestive process and also helps protect against bacterial overgrowth. As such, low levels of stomach acid are associated with greater occurrence of gastrointestinal issues such as constipation and SIBO. Hypothyroidism is frequently accompanied by a notable decrease in stomach acid levels. Therefore, reduced thyroid function may increase the risk of SIBO by triggering a decline of stomach acid and inhibiting digestion.

Protect Your Health by Supporting the Gut and Thyroid

SIBO and hypothyroidism are both complicated conditions and their frequent pairing with one another does not make diagnosis and treatment any simpler. Individuals with one condition often have the other. Ideally, patients who experience the signs and symptoms or have already been diagnosed with one of the conditions should pursue testing for the other.

At Holtorf Medical Group, our physicians are trained to utilize cutting-edge testing and innovative treatments to uncover and address both SIBO and thyroid disease. If you are experiencing symptoms of either SIBO or thyroid disease, or if you’ve been diagnosed with either condition, but aren’t getting the treatment you need, call us at 877-508-1177 to see how we can help you!


1. Dukowicz, A. Lacy, B. Levine, G. “Small Intestinal Bacterial Overgrowth: A Comprehensive Review.” Gastroenterol Hepatol (NY). 2007 Feb; 3(2): 112-122.
2. Ebert, E. “The thyroid and the gut.” J Clin Gastroenterol. 2010 Jul;44(6):402-6.
3. Patil, A.D. “Link between hypothyroidism and small intestinal bacterial overgrowth.” Indian J Endocrinol Metab. 2014 May-Jun; 18(3): 307–309.
4. Yayiali, O. Kirac, S. Yilmaz, M. Akin, F. Yuksei, D., et. al. “Does Hypothyroidism Affect Gastrointestinal Motility?” Gastroenterol Res Pract. 2009; 2009: 529802.
5. NAH Staff. “Are Your Digestive Issues Related To Your Thyroid? — SIBO and Hypothyroidism.” National Academy of Hypothyroidism.
6. Chris Kresser. “The Hypothyroidism-SIBO connection.” Kresser Institute.
7. Amy Myers, MD. “The SIBO and Hypothyroidism Connection.” Amy Myers, MD.

About Holtorf Medical Group

The Holtorf Medical Group specializes in optimizing quality of life and being medical detectives to uncover the underlying cause of symptoms, rather than just prescribing medications to cover-up the symptoms. We are experts in natural, prescription bioidentical hormone replacement and optimization, complex endocrine dysfunction, fibromyalgia, chronic fatigue syndrome and Lyme disease.

We’ve dedicated our practice to providing you the best in evidenced-based, integrative medicine that’s not only safe and effective, but provides measurable results.