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  • Writer's pictureDr. Jen

Unraveling Types 1, 2, and 3




Thyroid hormones are essential for maintaining an array of physiological processes, from our metabolism to our body temperature. At the heart of this intricate system are deiodinases, a family of enzymes that play a vital role in regulating thyroid hormones. Today, we'll dive deep into understanding Types 1, 2, and 3 deiodinases and their roles in thyroid health. (Save this blog post and share it!)


What are Deiodinases?

Before we delve into the specifics of each type, it's essential to grasp what deiodinases are. Simply put, deiodinases are enzymes responsible for activating or deactivating thyroid hormones by adding or removing iodine atoms. They ensure the right balance of active and inactive thyroid hormones in various tissues. These can have genetic SNPs or single nucleoside polymorphisms. These are genetic and if present can make these enzymes less effective.


Type 1 Deiodinase (D1)

Role and Location: D1 is primarily involved in converting the prohormone thyroxine (T4) into the active hormone triiodothyronine (T3). This process is termed "outer ring deiodination." D1 is predominantly found in the liver, kidneys, and thyroid. Liver health plays a huge role here and most of T4 --> T3 conversion occurs in the liver!

Significance: As a major source of circulating T3, D1 plays a crucial role in maintaining our body's overall metabolism. By converting T4 into T3, D1 helps keep a check on the levels of active thyroid hormone in our bloodstream.


Type 2 Deiodinase (D2)

Role and Location: D2 is primarily tasked with the intracellular conversion of T4 into T3. Found in tissues like the brain, pituitary, and brown adipose tissue, it ensures that cells in these regions have a steady supply of active thyroid hormone, irrespective of circulating levels.

Significance: D2 plays a fundamental role in feedback mechanisms. For instance, in the pituitary, it helps maintain T3 levels, which in turn influence the secretion of thyroid-stimulating hormone (TSH) – a hormone responsible for signaling the thyroid gland to produce more T4.


Type 3 Deiodinase (D3)

Role and Location: Unlike D1 and D2, D3 is primarily an inactivating enzyme. It converts T4 into reverse T3 (rT3) and T3 into diiodothyronine (T2), both of which are inactive forms. D3 is found in high concentrations during fetal development in the placenta and in the adult central nervous system, among other tissues.

Significance: D3 acts as a protective mechanism. By inactivating thyroid hormones, it ensures tissues aren't exposed to excessive active thyroid hormones, which can be particularly crucial during specific developmental stages like pregnancy.


In Conclusion

The triad of deiodinases plays a crucial role to regulate our thyroid hormone levels. While this may be confusion. If you have a good team for your health you can be assured that all of these factors will be addressed. Want to work with me or someone on my team? Check out work with us for more information!




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