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Conversion of t4 to t3 thyroid hormone

Traditional health practitioners screen thyroid function by looking at one main lab value called thyroid stimulating hormone (TSH). The pituitary gland in your brain releases TSH which then tells your thyroid gland to make thyroid hormone (abbreviated T4).

However, your body must convert T4 into T3 (the active form) in order to use it. If the conversion of T4 to T3 is poor, then you may experience some of the common hypothyroid symptoms like fatigue, depression, sensitivity to cold temperatures, difficulty concentrating, and more. Keep in mind, that this poor conversion can occur even if your TSH levels appear to be normal. So, it’s important to assess the conversion of T4 to the active…

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The Challenges and Complexities of Thyroid Hormone Replacement

Historically, patients with hypothyroidism were treated with crude thyroid extracts, containing T4, T3, and other compounds. With the discovery of T4, therapy shifted to use of this purified compound. Subsequent synthesis of T3 lead to the introduction of a combination T4 and T3 therapy, which for several decades was considered the acceptable standard. However, it was observed that combination therapy often led to hyperthyroidism due to an excess T3, and as a result, current guidelines from the American Association of Clinical Endocrinologists recommend that clinical hypothyroidism be treated with synthetic T4 (levothyroxine) alone.

Triiodothyronine T3

The thyroid only creates a small amount of T3. However, it produces T4 in higher quantities. T4 is inactive, but enzymes in the body can turn it into activated T3 or reverse T3 (rT3.) The conversion into active T3 happens in the kidneys, liver, muscles, and thyroid gland, while enzymes in the brain and placenta can turn T4 into rT3.

Understanding Thyroid Hormones: What Is the Difference Between T3 and T4?

T4 contains four iodine atoms, and T3 contains three. Hence, the numbers in their respective acronyms. T4 is also the inactive form, while T3 is the active counterpart which means tissues need to convert T4 into T3 by removing an iodide through selenium-containing enzymes. This process is called deiodination. Moreover, T4 is only produced by the thyroid gland and cannot be formed elsewhere. On the other hand, T3 is created in the thyroid gland and some other organs

What Is Reverse T3?

Why is this a potential problem? Reverse T3 can bind to a cell in the same way T3 does, except when reverse T3 binds to it, nothing happens. When this happens, Dr. Rose explains, “reverse T3 and T3 will then compete for receptors' at the cellular level. Your body can start showing symptoms of hypothyroidism when not enough T3 is binding to your cells.”

What Is T3 (Triiodothyronine)?

About 20% of your body’s T3 is delivered into your bloodstream by your thyroid gland. The other 80% is made by your liver or kidneys in a process called deiodination. In this process, your body converts T4 into T3, as T3 is the biologically active form of the thyroid hormone T4. This is why patients with underactive thyroids take synthetic T4 as medication.

Resources

Cytomel

Liothyronine is synthetic T3.

PsychDB

Triiodothyronine (T3) (also known as liothyronine) is the active form of the thyroid hormone, thyroxine. Approximately 20% of T3 is secreted into the bloodstream directly by the thyroid gland. The remaining 80% is produced from conversion of thyroxine by organs such as the liver and kidneys. In psychiatry, liothyronine is sometimes used as an augmentation medication for depression in combination with antidepressants.

You and Your Hormones

Triiodothyronine is the active form of the thyroid hormone, thyroxine. Approximately 20% of triiodothyronine is secreted into the bloodstream directly by the thyroid gland. The remaining 80% is produced from conversion of thyroxine by organs such as the liver and kidneys. Thyroid hormones play vital roles in regulating the body’s metabolic rate, heart and digestive functions, muscle control, brain development and function, and the maintenance of bones.