Thyroid Hormone Conversion

I always encourage anyone suffering from a chronic condition to develop their understanding of what is driving their disease. Thyroid conditions are complex in nature and there are an array of individual reasons as to why thyroid hormone conversion can be slow. This post covers just some of the problems that should be investigated. 

Respect and pray on nature background


Reactions that catalyse the conversion of thyroid hormones are triggered by enzymes called deiodinases. For this article we will called them type 1 (D1), type 2 (D2) and type 3 (D3). These deiodinases are responsible for the regulation and bioactivity of thyroid hormones, the conversion of T4 to T3 and reverse T3 (rT3), T3 to T2, rT3 to T2 and the degradation of thyroid hormones.

The thyroid gland has an exceptionally high selenium content, with more selenium per gram of tissue than any other organ. The body possesses compensatory mechanisms that conserve selenium in the thyroid with deiodinases ranking high in the hierarchy for selenium supply. This maintains deiodinase function when selenium levels decrease elsewhere in the body. Studies show that selenium has to become severely deficient for thyroid conversion to be affected. This does not mean that we can neglect our intake of selenium as low levels will have negative consequences for our thyroid and immune system. 


There are a number of  mechanisms that will reduce deiodinase function and therefore cause thyroid hormone conversion issues. D2 is downregulated in the presence of high amounts of T4 with a much shorter half-life. If T4 is low D2 is upregulated to convert more T4 to T3. In simple terms, the higher the T4 the less the body will convert to T3. This could explain why patients continue to experience thyroid symptoms or feel worse when a doctor prescribes higher and higher amounts of thyroxine.

The thyroid gland has an exceptionally high selenium content, with more selenium per gram of tissue than any other organ. 

In healthy individuals the regulation of thyroid hormones is under tight control. However, acute and chronic illness can lead to Non-Thyroidal Illness Syndrome (NTIS), disrupting D1 activity and reducing deiodinase conversion activity. The presentation of NTIS is abnormally low TSH, depressed T3 levels, low D1 and increased D3 activity leading to high rT3. Prolonged illness can also cause low T4.

NTIS can present during any critical illness such as sepsis, heart attacks and advanced kidney disease. Patients with ongoing inflammation and high oxidative stress in chronic conditions such as Crohn’s Disease can also experience NTIS. They will very likely experience an increased demand for selenium, lower GPx and potentially altered thyroid metabolism as explained in my previous post. Here is a good example of treating the body as a whole rather than separating gastroenterology from endocrinology. All the symptoms are intimately linked and affect each other. Could T3 medication provide some relief during a Crohn’s flare and increase the ability of the body to metabolise nutrients and therefore speed up the healing process?

Studies have shown that the inflammatory cytokines IL-1, IL-6 and TNF-alpha, which are released during the stress response, affect thyroid hormone conversion, reducing T4 conversion to T3 and also increasing rT3, the inactive thyroid hormone. This leads to reduced T3 and therefore increased incidence of under-active thyroid conditions.

Another factor that can affect thyroid hormone conversion is poor gut health, also known as dysbiosis. Lipopolysaccharides (LPS), found on the outer membrane of gram negative bacteria, can cause intestinal permeability, dysbiosis and autoimmunity. LPS can impact deiodinase activity inhibiting the amount of T3 in circulation. We cannot have good thyroid health without good gut health. 

Lastly, but definitely not least, check you are getting enough zinc in your diet or through supplementing with Food-Grown Zinc, as this mineral is important for thyroid hormone conversion.

If you are thinking about having a Nutritional Therapy appointment please visit my home page to read about what I provide during a consultation. I offer all potential clients an informal free 10 minute conversation over telephone. This is not a consultation, but an opportunity to understand how the process works and ask any questions you may have. It is also a chance to hear my voice and get a sense of my practice style. You are in no way obligated to book afterwards.

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October 17, 2017 2:54 pm Published by