What are T4, T3 and reverse T3?
The human thyroid gland is a butterfly-shaped gland in the front of the neck. This gland produces and secretes two thyroid hormones called T4 and T3. It is T3 that acts on the cells to increase metabolism, pulse rate, and body temperature.
T4 is a storage hormone, which in itself is inactive but is converted to the active thyroid hormone T3. This convention takes place mainly in the liver and partly in the tissues. Under normal circumstances, small amounts of T4 are also converted into what is called reverse T3 or rT3.
What is the danger of Reverse T3?
Reverse T3 is an inactive form of T3. Reverse T3 is produced from T4 instead of the active thyroid hormone T3. Overproduction of reverse T3 is dangerous because it binds to T3 receptors on cells, but it doesn’t increase the metabolic rate as T3 does, which is why it is considered inactive. In effect, it blocks T3 at a cellular level. Put in another way it lowers the metabolic rate by binding to the T3 receptor instead of T3.
The amount of reverse T3 produced is as mentioned usually very small. However, reverse T3 production can increase with illness, stress or inflammation, starvation, low blood sugar, and so forth!.
Reverse T3 is an evolutionary adaptation. During times of stress, famine or starvation, reverse T3 increases, to slow the metabolic rate and conserve energy.
Another situation where the body overproduces reverse T3 is when the body senses too large an amount of T4, such as will be the case if a hypothyroid person with a conversion defect uses a T4 only medication. The overproduction of reverse T3 happens as a reaction to the accumulated T4, resulting in a strong anti-thyroid effect.
Will High T4 produce reverse T3?
One would think that a thyroid medication for treating low thyroid function would always contain the same ratio of hormones as the natural gland produces, but that is not the case.
Most people with low thyroid function are treated with T4 only medications, some common brand names are Synthroid, Levoxyl, L Thyroxine, Levo T, Levothroid, Levothyroxine.
The effect of synthetic T4 medication was tested on healthy young male students, and in those individuals, T4 works perfectly as healthy young males have strong livers and thus have no problem converting T4 to T3.
However, women and or sick or stressed people who have weaker liver function often have issues with the conversion of the inactive T4 to the active T3.
People on pure T4 medication often feel they need to increase their thyroid medication as their symptoms of low thyroid function persist. But increasing the use of T4 can create problems if it is not converted to T3. The accumulated T4 increases the production of reverse T3, which lowers thyroid function by competing with T3 on the cellular level.
How do you treat high reverse t3?
Usually using a combination treatment with both T4 and T3 is helpful in avoiding the issues with accumulated T4 and increased reverse T3. The combination treatment could be in the form of a natural desiccated thyroid supplement or it could be a combination of synthetic T4 and T3.
Our Hypothyroid Treatment Program Module 16 goes into detail about the best medications for hypothyroidism. You can also learn more about medication in our thyroid medication blog post and get guidance on the best types of natural thyroid supplements in our thyroid supplement guide.
Do I need Pure T3?
In some cases using a pure T3 medication is the best way to treat a high reverse T3 level. The higher amounts of T3 have the ability to clean the receptors for reverse T3 and reset our thyroid function.
People that have been very sick or stressed for a long time sometimes need treatment with a pure T3 for a while before a more natural combination of T4 and T3 can be introduced with success.
BiochemNordic does not prescribe medication but we often work with people that are on prescription thyroid medication from their doctor. If you need help with your thyroid function or handling your thyroid medication we offer online thyroid consultations. Since taking a thyroid supplement or medication is not always easy you might need help as your body changes and reacts to the medication. It is important to have an experienced thyroid specialist to help you handle the adjustments to your metabolism and hormonal balance in general.