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Thyroid Health – Understanding Reverse T3

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Thyroid Hormones - Reverse T3

The thyroid is a critical element in one’s overall health. This is because the hormones secreted by the small butterfly-shaped gland interact with every cell in the body and influence their function. A malfunctioning thyroid can lead one to experience significant health issues or develop thyroid-related disease such as hypothyroidism and hyperthyroidism. Being better informed on what Reverse T3 is, what it does, and the great value that comes from including it in thyroid blood testing can help one support optimal thyroid function.

Intro to Thyroid Hormones

The two most prominent hormones produced by the thyroid are thyroxine (T4) and triiodothyronine (T3). But there are others involved in maintaining a healthy thyroid and ultimately a healthy body. One such hormone that is wrongly invalidated by many endocrinologists is reverse triiodothyronine (Reverse T3). Because of inadequate appreciation or understanding of the impact Reverse T3 has on the body, many have been left to unduly suffer from a thyroid imbalance.

There are several hormones secreted by the thyroid. The three most important hormones regarding thyroid disease and cellular function are:

  • T4, known as the storage or inactive form of thyroid hormone, is the hormone most produced by the thyroid.
  • T3, called the active form of thyroid hormone, is five times more active than T4.
  • Reverse T3, the inactive mirrored form of T3, inhibits T3 function.

Before the body can fully utilize thyroid hormone, it must be converted from T4 into the active form T3. T4 is capable of being converted into either T3 or Reverse T3 depending on the removal of specific iodine atoms. By removing a certain iodine atom, T4 is converted into T3. Alternatively, if a different iodine atom is removed, the result is Reverse T3. This process of T4 conversion is known as monodeiodination.

In a properly functioning thyroid, roughly 40% of T4 is changed to T3 and about 20% is translated into Reverse T3 daily. However, if one’s thyroid is malfunctioning, or if the body needs to conserve energy and is under significant stress, the conversion ratio may change to 50% of T4 becoming Reverse T3. A significant change such as this greatly impacts thyroid function and hormone availability.

A Closer Look at Reverse T3

Reverse T3 is the mirrored inactive form of T3 and is instrumental in keeping thyroid hormone levels in balance. Without the presence of Reverse T3 in one’s system there is great risk that their T3 levels reach dangerously high levels resulting in a severe case of hyperthyroidism (an overactive thyroid frequently caused by excess T3). Alternatively, too much Reverse T3 overly inhibits T3’s ability to provide energy and oxygen to one’s cells resulting in reduced metabolic function on a cellular level. Reverse T3 and T3 compete for the same receptors throughout the body. If there is a greater prevalence of Reverse T3 in one’s system, it will effectively block active thyroid hormone from reaching cells. Maintaining the appropriate ratio of T3 to Reverse T3 helps keep the body running smoothly.

As an effective T3 inhibitor, Reverse T3 helps the body maintain a proper balance of active thyroid. Not only does it block receptor sites but it influences conversion of T4 into other hormones. Studies have found that Reverse T3 can be 100 times more effective at reducing the conversion of T4 into T3 than Propylthiouracil (PTU), a treatment option for those with hyperthyroidism. Although this regulatory action is useful for maintaining proper thyroid hormone levels, if Reverse T3 is overproduced it can cause severe hypothyroidism. Those who have hypothyroidism generally see an increase in symptom severity when there is an overabundance of Reverse T3 in their bloodstream.

Contributors of Hormone Imbalance

Thyroidal dysfunction is not the only possible cause of increased Reverse T3. Stress-related hormones can further compound a Reverse T3 imbalance. When there is an excess of Reverse T3 in one’s system their metabolism slows leaving them feeling sluggish and tired. To counteract this, the body releases cortisol, also known as the stress hormone, to increase alertness and energy. Although this temporary mental boost has many uses, especially when one is in physical danger, if it is relied on as a primary source of energy various problems develop. Regular release of cortisol, due to chronic stress, T3 deficit, or excess Reverse T3, can exhaust the adrenals, causing one to experience long-lasting fatigue. Furthermore, cortisol inhibits T4 to T3 conversion, resulting in increased prevalence of Reverse T3 in one’s system.

Other conditions that contribute to increased Reverse T3 levels include:

  • Chronic fatigue
  • Acute illness and injury
  • Chronic disease
  • Increased cortisol (stress)
  • Low cortisol (adrenal fatigue)
  • Low iron
  • Lyme disease
  • Chronic inflammation

Poor Testing Practices

Unfortunately, a large portion of the medical community still believes that Reverse T3 is an unimportant factor in one’s thyroid function. This has caused most practitioners to rely on thyroid stimulating hormone (TSH) and T4 testing alone to analyze one’s thyroid function. These tests do not account for conversion issues or recognize if there is an overabundance of Reverse T3 in one’s system. Even if T4 and TSH levels fall within the “normal” range, one may still experience health issues if there is excess Reverse T3.

According to a study in The Journal of Clinical Endocrinology & Metabolism, TSH and T4 levels are poor indicators of one’s thyroid function. It was further stated that the use of these tests alone do not reflect an appropriate image of thyroid health for a significant percentage of patients. Relying solely on tests that neglect Reverse T3 can leave patients suffering from undiagnosed thyroid dysfunction for years. Thankfully a growing number of holistic and integrative medical practitioners, particularly those who specialize in hormone balance, are vocalizing the importance of Reverse T3 testing for diagnosis and treatment.

Using All the Pieces

Because Reverse T3 is such a critical element for thyroid function, it is important to have appropriate testing. If you are experiencing hypothyroid symptoms while your thyroid blood panel tests present normal TSH and T4 levels, it is important that you get your Reverse T3 levels tested as well. Without having a clear picture of the numerous elements impacting thyroid function it is near impossible to properly diagnose and treat one’s unique condition. If you have thyroidal concerns, make sure Reverse T3 is included in your thyroid blood test panel.

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9 Comments on "Thyroid Health – Understanding Reverse T3"

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Mary Vale
I have both type 1 diabetes and hypothyroidism. I am being treated with levothyroxine and insulin. However the thyroid tests are coming back with the T3 levels at .006 … they are cutting my levothyroxine, but I have all of the symptoms of hypothyroidism… I weigh over 200 lbs now, with my normal weight being 150 lbs. …. and am cold especially my feet and legs… I am tired, my tongue is swollen and I cannot function like I used to due to brain fog. My skin is dry and itchy but it could be the diabetes too. I have… Read more »
Naomi Parker

Hello Mary,
Levothyroxine is a T4-only medication. If you are on it and are still experiencing extremely low T3 levels, you and your doctor should consider either a combination (T4/T3) or straight T3 medication. You are probably experiencing what’s going on in this article: your T4 is likely converting mainly to RT3 which is the exact opposite of T3.

I hope this information helps!

– Naomi

Debbie Stevens

What is normal reverse T3 levels? Thanks.

Naomi Parker

Hello Debbie,
Here is a good calculator to determine if your RT3 is in a good range. The RT3 always needs to be looked at in conjunction with your T3 levels.

I hope the information helps!

– Naomi

I was wanting to get someone else’s opinion and was wondering if you could help? My doctor said my reverse T3 is a little high in comparison to my free t3 level. Technically it still in the lab results reference range. She initially said all my thyroid levels was all normal but then I called back bc I’m in my first trimester of pregnancy and I know tsh should be under 2.5 and mine is 4.3. She said to talk to my endo about my rt3/freet3. So when I called back I told her I don’t have an endo so… Read more »
Naomi Parker

Your doctor did the right thing! High RT3 does NOT mean you’re getting too much T3, especially when you have lab results to back this up. What is likely happening is you’re converting more of your T4 to RT3 rather than T3. Additionally, 5mcg is an extremely small dose and will not likely have a great impact.

I hope this information helps!

– Naomi

Holly Hanson

My reverse t3 is 30 the standard is 10 -24ng is mine considered high what should be done. My primary Dr. Thinks is normal

Naomi Parker

Hello Holly,
You’re right to think that the RT3 is not “normal”. Here is a ratio calculator to determine your RT3 range: It is highly likely that your T4 is converting more to RT3 than T3. Without getting into your treatment protocol, if you’re currently undergoing a T4-only treatment, it may be a good idea to discuss a combo (T4/T3) or T3-only treatment.

I hope this information helps!

– Naomi

Hi there, Just want to say THANK YOU so much for this informative article. I am almost 4 months post Thyroidectomy and very uninformed between my family doctor, Endo and ENT Surgeon. I’ve even had my family doctor tell me theres no such thing as Reverse T3. I start seeing a new Specialist next month and hope he will treat me based on what I ask, to which I plan to as for more thorough testing. I unfortunately think I am a prime candidate for my body to convert my T4 to RT3 due to high stress. Would a Thyroidectomy… Read more »

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