More than 12% of Americans will experience a thyroid disorder at some point in their lives according to the American Thyroid Association. The two most common thyroid disorders are hypothyroidism (an under-functioning thyroid gland) and hyperthyroidism (an over-functioning thyroid gland). Because the body functions as one inter-connected whole system, thyroid disease often affects gastrointestinal function and gut disorders often affect the thyroid. This is why it is important that physicians always evaluate and treat patients comprehensively in order to achieve the best treatment results.

How do thyroid hormones affect gut health?

Thyroid hormones affect the GI tract in many different ways. Thyroid hormones are essentially responsible for your metabolism, meaning an excess of hormones can speed up intestinal movement and a deficiency slows things down. It is very common for hyperthyroidism to cause diarrhea and malabsorption of essential vitamins and minerals. In contrast, a deficiency of thyroid hormones often causes constipation. Hypothyroidism can also delay stomach emptying, which can lead to difficulty swallowing or reflux symptoms. In patients with constipation-dominant SIBO (small intestinal bacterial overgrowth), comprehensive thyroid hormone blood testing is imperative. In my practice, I find that about 25% of the time I uncover a clinical or subclinical hypothyroid state that is contributing to SIBO symptoms.

How does the gut affect thyroid health?

The connection between the GI tract and thyroid gland is both complex and extensive. Our intestinal bacteria and also the integrity of the mucosal lining of the small intestine play a large role in our absorption of many vitamins and nutrients. Thyroid hormone production is dependent on certain nutrient cofactors including iodine, tyrosine, zinc, selenium, iron, and B12. 

Inflammation in the gut is also directly linked to autoimmune thyroid disease. The gut microflora is a large regulator of the immune system, and a healthy immune system is necessary to keep autoantibodies from causing disease in those that are genetically predisposed. The most common autoimmune thyroid disease is Hashimoto’s thyroiditis. This condition happens when certain autoantibodies attack thyroid cells and over time damage the thyroid to the point where it begins to under-function. Conventional doctors tend to ignore thyroid antibodies and simply treat Hashimoto’s by prescribing thyroid hormone to restore patients to normal hormone levels. While thyroid supplementation is necessary, it is not actually treating the autoimmune reaction at all.

Many patients with Hashimoto’s disease have underlying intestinal inflammation that is feeding their autoimmune response. Treatment with a combination of food intolerance removal and anti-inflammatory supplements can lower inflammation for many patients and over time reduce their thyroid antibodies as well. Direct supplementation with zinc, selenium, and B12 can also help lower antibodies for many patients.

What is a full thyroid panel?

Although much has been learned about the importance of running a full thyroid panel when screening for thyroid disorders, many physicians still only look at TSH (thyroid stimulating hormone) values. While this test will pick up more severe thyroid disease, it is not so good at identifying moderate and mild cases. And I can tell you from clinical experience, mild to moderate disease can still cause significant symptoms! A full thyroid panel typically consists of these tests: TSH, free T3, free T4, reverse T3 (in some cases), and TPO/thyroglobulin antibodies.

Dr. Katie Nuckolls is a naturopathic physician and owner of Thrive GI: Natural Digestive Medicine in Vancouver, Washington. She currently sees patients that live in Washington, Oregon, and Arizona using telemedicine. For more information, visit our contact page or schedule a free 15-minute consultation online.  

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