What is Reverse T3

So, we just got our blood test results from our doctor including our T3 and T4 levels and they are aligned — within range.  So, what does the “within range” signify and is that all there is to know about them?  Basically, what does T4 and T3 mean?

In biochemistry language, T4, has 4 iodines attached to a double tyrosine backbone while T3, as the number implies, only has 3 iodines.  

These days when we are all under a great deal of stress, there is a need to produce more energy or heat. Our bodies do this by the body’s ability to rev up the thyroid conversion process to produce more T3 from T4. 

The opposite is also true where the body can slow down this conversion and put energy into more important bodily functions in instances where you may be critically ill.

T3, is the “forgotten troublemaker” in the family as discussed by Sanctuary Functional Medicine.  Reverse T3, like its mirror image T3, has 3 iodines attached to a double tyrosine backbone.  Problems arise when T3 and Reverse T3 cross paths. 

To put it another way, the presence of reverse T3 (rT3) will literally block thyroid hormone receptors which makes normal T3 unable to bind. This means if your endocrinologists actually test T3 or free T3, those levels might look good, but the presence of the rT3 will inhibit the T3 from being effective.  It can be like a disconnected gas pedal that when depressed and nothing happens. 

T4 floats around the body and gets turned into the more active T3 when an iodine is removed.  If a different iodine is removed, the T4 turns into Reverse T3, which in turn, deactivates T4’s benefit of turning into T3.

Situations of inflammation, high cortisol (stress), and some toxins, the T4 turned into Reverse T3 increases and thus wastes the T4 produced in the thyroid. In some conditions, the T4 is converted into T3 at a slower rate, and this particularly occurs when there is low zinc or low selenium or low vitamin D.

While conventional medicine forgets that measuring Reverse T3 helps, functional medicine identifies patients deactivating too much of their T3.  When we see an elevated Reverse T3 in the lab, especially if combined with a low T3, then it is suspected one of these conditions mentioned above and search for the cause behind the observed high Reverse T3 effect.

We do this because we know that optimizing the T3 – Reverse T3 balance helps relieve hypothyroid symptoms that go unrecognized by conventional medicine only watching the TSH.  


For more detailed information on this check out Sanctuary Functional Medicine, under the direction of Dr Eric Potter, IFMCP MD

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