A healthy thyroid produces T4, T3, and in smaller amounts T2, T1 and calcitonin. As discussed, T4, the storage hormone is meant to convert to T3 the active hormone.
However there is another substance produced by the thyroid called Reverse T3, it also comes from the conversion of the storage hormone T4 and it is quite normal to have some RT3.
Your liver can constantly be converting T4 to RT3 as a way to get rid of any unneeded T4 and maintain homeostasis (balance of all critical bodily functions). In any situation where your body needs to conserve energy and focus on something else, for example during illness, injury, high levels of stress or a dramatic lowering of environmental temperature, the conversion rate of T4 to T3 or RT3 will change.
Additionally, certain physiological conditions cause T4 to be converted to RT3, including adrenal dysfunction (low cortisol, high cortisol), low or high iron levels, low B12 and chronic inflammation.
Given that RT3 is a ‘mirror molecule’ of normal T3, is intrinsically inactive and prevents proper activation of receptor sites, which in simple terms stops the active T3 from entering the cells where it is needed for all metabolic functions, it is critical that the level of RT3 remains in correct balance with T4 and T3. Therefore testing for RT3 levels at the same time as FT4 and FT3 is vital.
When testing for RT3 you are not necessarily looking for a blood level high in the range, but a problem in the ratio between RT3 and Free T3. By dividing the Free T3 by the Reverse T3 (Free T3 ÷ RT3), all in the same measurement unit, the ratio should be 20 or greater. If using the total T3, the ratio should be greater than 10.
Remember, it is vital that you be tested for RT3, do not take no from your doctor who doesn’t believe in such witchcraft!
Here is a fun fact to reiterate the importance of rebalancing the conversion of T4 to T3 instead of RT3. When bears prepare for hibernation, in order to survive the long cold winter of their environment, their bodies produce RT3. By doing so their systems shut down to a point of barely functioning – very low heart rate, low body temperature, impaired digestive function, increased sleep requirements, and the list goes on. This is akin to our bodies preparing for famine, every function reduces to the most basic level in order to conserve energy and survive the dire period ahead.
Now we, as humans do not need to hibernate and generally, in the western world at least, do not face periods of famine so we definitely do not want our metabolic systems to slow down, we want to live life to the fullest!