How the three deiodinases regulate T3

Dear thyroid patients: If you’ve never heard about the deiodinases, your life and future health may depend on you learning about them.

The deiodinases can either work with your thyroid meds or against them.

It’s a lifelong condition, being on thyroid therapy, so there’s time for thyroid knowledge to sink in. I don’t have a bioscience degree and I eventually got this.  I’ll try to make it as simple as possible. Try not to be intimidated if it’s new to you. There are only some new words and concepts to learn, and learning them will help you defend your T3 hormone and your health.

Let’s get started.

First of all, what is a “Deiodinase”?

A deiodinase is an enzyme that converts thyroid hormones from one form to another.

Thyroid Hormone Metabolism

“Iodine” is at the root of the word “Deiodinase.”

This is because It performs its action by removing one iodine atom from the hormone molecule.

Therefore, a deiodinase “De – IODINE – ates” the hormone molecules, enabling them to change their structure and function as thyroid hormone.

The thyroid hormone begins its life as T4 or T3.  Yes, you read that correctly.  Most doctors don’t know this yet. A recent article has proven a revolutionary fact: Some T3 is created “de novo” (it’s born as T3) within the thyroid gland (Citterio et al, 2017).  This discovery is important for people whose gland is either completely removed, or mostly dead after autoimmune attack. It means you can’t create as much of your own T3 anymore. An important T3 factory that other people have is under-producing or entirely missing.

T4 is converted into a form of T3, then T3 becomes T2, and finally, T1. (There are also other minor metabolites created along the way, but I won’t get into those right now. As this process occurs in thyroid hormone metabolism [activation, transformation] and catabolism [breakdown], we call the byproducts “thyroid hormone metabolites.”)

The deiodinases’ activity upon thyroid hormones are an important part of the body’s method of circulating iodine, and just the right amount of iodine (not too much, not too little) is essential for the thyroid gland to produce thyroid hormone.

The most important hormone in this cycle is T3, since it is the only hormone known to trigger a huge series of “genomic” activities within the thyroid hormone receptor located in every cell throughout our body.

That means it turns on and off genes that are just waiting to be activated by T3.

When the receptor does not have T3, it’s off. When the receptor has T3, it’s on, like a light switch.

Sorry, but T4 can’t do this.

Without T3, our body cannot make energy.

Without the perfect amount of T3, not too much and not too little, our cells, organs and tissues, yes–even our brain–cannot function properly.

Unfortunately what doctors don’t seem to understand is that TOO LITTLE T3 is just as dangerous as too much, and when we lack it, and we can’t make enough of it out of T4 (and many on T4 meds cannot), we truly need it from T3-based medication.

Deiodinase type 1 (D1)

  • The DIO1 gene is responsible for creating the Deiodinase type 1 enzyme.
  • Deiodinase type 1 converts T4 to T3 in the bloodstream for the cardiovascular system. The availability of T3 in blood plasma and serum is vital for organs that depend on T3 from this source.
  • The bloodstream is the “entry point” for thyroid hormones to flow into the rest of the body. If you are a bit low in T3 in blood, you may have a further deficit depending on your Deiodinase type 2.

Deiodinase type 2 (D2)

  • The DIO2 gene is responsible for producing the Deiodinase type 1 enzyme.
  • Deiodinase type 2 converts T4 to T3 in cells and tissues for organs that are “peripheral” to the bloodstream, such as bone, brain, muscle, skin. TSH plays a role in upregulating Deiodinase type 2 to convert T4 to T3 in just the right amounts needed within each cell and tissue

Deiodinase type 3 (D3)

  • Deiodinase type 3 is a lot more complex.
  • It reverses the process of hormone conversion by slowing down D2 and D1.
  • It converts T4 to Reverse T3 and converts T3 into T2, and it does this in both the bloodstream and peripheral tissues at the same time.
  • Learn about its function, activity, and measurement in a separate blog post:

4 thoughts on “How the three deiodinases regulate T3

  1. Pingback: Deiodinase type 3 and Reverse T3 – Canadian Thyroid Patients Campaign

  2. Pingback: Dosing by the TSH can cause Low T3 – Canadian Thyroid Patients Campaign

  3. Pingback: REVIEW: Dr. Antonio Bianco’s 2016 interview on hypothyroidsm – Canadian Thyroid Patients Campaign

  4. Pingback: Infographic: The dangers of Low T3 Syndrome – Canadian Thyroid Patients Campaign

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