rT3 - the silent saboteur of your metabolism

Today will be about the "secret hormone", which I am sometimes asked about by patients, and also sometimes by colleagues interested in the topic of weight loss who have other specialties.

rT3 is part of our hormonal endocrine puzzle, and knowing that the hormone exists can help explain many situations related to our health, especially if we are experiencing weight loss problems, fatigue, sluggishness, impaired concentration, and even full-blown symptoms of brain fog. A person with an elevated rT3 concentration may even have an ideal TSH, and may complain of fatigue, and this does not at all mean that such a person is lying.... It is then worth ordering a determination of reverse triiodothyronine (rT3, reverse T3), which is the inactive form of the hormone triiodothyronine (T3), one of the main hormones produced by the thyroid gland. Triiodothyronine (T3) and thyroxine (T4) are key hormones responsible for regulating metabolism in the body. rT3 is formed from thyroxine (T4) by enzymatic conversion, which occurs mainly in the liver, kidneys and other peripheral tissues.

So what is the function of rT3 in our body?

It's worth realizing that rT3 is a metabolically inactive metabolite, meaning that it doesn't affect metabolism the way the active form of T3 does. Rather, it acts as a regulator, blocking receptors that would normally be activated by T3. In this way, it reduces metabolic activity, which is particularly useful in situations where the body needs to conserve energy, such as during stress, starvation or illness.

When does the formation of rT3 occur in our body?

Well, this is a kind of adaptive mechanism. In states of stress, starvation, severe illness or injury, the body often converts more T4 into rT3 to reduce metabolic activity and conserve energy for basic vital functions. As we know, thyroxine (T4) can be converted in basically two ways: into active triiodothyronine (T3) or into inactive reverse triiodothyronine (rT3). This process depends on enzymes called deiodinases, which cut iodine atoms from T4. Depending on the body's physiological conditions, more T4 may be converted to rT3 in situations that require a reduction in metabolism, such as stress, chronic illness or inflammation.

So what is the clinical role of rT3?

Well, rT3 levels are rarely routinely tested, but can be useful in evaluating conditions in which thyroid hormone metabolism is impaired, such as in low triiodothyronine syndrome or other chronic diseases. It is also useful for assessing the conversion of T4 to T3 in our body.

In summary, rT3 is an indicator of metabolic changes in the body that affect energy conservation and can lead to hypothyroidism-related disorders if its levels are too high.

If you have been diagnosed or have diagnosed yourself with elevated levels of reverse triiodothyronine (rT3), this may suggest a disorder in thyroid hormone metabolism. rT3 is the inactive form of triiodothyronine (T3) and is mainly formed by the conversion of thyroxine (T4) in the body.

Elevated rT3, as I have already mentioned, can occur in situations where our body is subjected to physiological stress, in situations such as chronic diseases: kidney failure, liver failure, heart failure or cancer. It can also accompany a state of starvation or cachexia. Caloric deficiency, especially in a low-carbohydrate diet or in a state of starvation, can lead to an increase in rT3 concentrations, as our body then reduces metabolic activity to conserve energy.

Chronic physical or psychological stress, as well as trauma, surgery or infections, can affect the increase in rT3 levels. The cause of excessively high rT3 may be improper conversion of thyroid hormones: Problems with the conversion of T4 to active T3 (e.g., due to selenium or zinc deficiency) can lead to an increase in rT3 at the expense of T3. When this happens, symptoms of hypothyroidism are also observed, even though TSH levels may be normal, which sometimes greatly surprises patients, as well as some of our non-endocrinologist physician colleagues.

Low triiodothyronine syndrome is a condition seen in severe diseases when the body deliberately reduces thyroid hormone activity by increasing rT3 to slow down metabolism.

High rT3 by itself does not always require treatment, but it may suggest the need for a more thorough diagnosis, especially for metabolic, stress or chronic disease causes.

Unfortunately, elevated levels of reverse triiodothyronine (rT3) can lead to a number of disorders related to thyroid function and overall body metabolism.

The main consequences and potential effects of long-term elevated rT3 levels include: symptoms of hypothyroidism. Despite normal or sometimes even slightly elevated levels of T4 (thyroxine) and normal TSH, high levels of rT3 can cause symptoms of hypothyroidism. This is due to the blocking of the active form of triiodothyronine (T3) by inactive rT3.

Symptoms can include fatigue, sluggishness, cold intolerance, weight gain, dry skin, problems with concentration and memory (known as "brain fog"), constipation and depression.

Elevated rT3 also leads to a slower metabolic rate, which can result in problems with weight loss or even weight gain, despite diet and exercise.

In the long term, this can lead to metabolic syndrome, insulin resistance and an increased risk of developing type 2 diabetes.

In addition, high rT3 is often observed in patients with chronic fatigue syndrome (CFS) or fibromyalgia, suggesting that endocrine disruption may contribute to the body's impaired ability to recover and maintain energy.

Since thyroid hormones affect immune system function, impaired hormone metabolism can lead to a weakened immune system, which in turn increases the risk of infections and problems fighting them.

Low levels of active T3 (resulting from high rT3 levels) can lower heart rate and stroke volume, which also leads to weakened heart function, reduced exercise tolerance and blood pressure problems. High levels of rT3, resulting in symptoms of hypothyroidism, can contribute to depressive states, anxiety, and problems with memory and concentration.

In athletes or physically active individuals, elevated rT3 can lead to reduced physical performance and slower recovery processes, making it more difficult to perform and improve fitness.

For this reason, it is important to identify the cause of elevated rT3 and implement appropriate treatment, which may include lifestyle changes or appropriate supplementation, chronic disease management or other medical interventions.

If you find that you have excessively high rT3 levels, it is best to direct your steps to an endocrinologist who can help you solve the problem.