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A Functional Medicine Approach to Thyroid Hormone Labs

Once the thyroid gets the TSH production memo, it produces a blend of active and inactive thyroid hormone. Of the thyroid hormone that is made and released at the level of the thyroid, 90% is inactive hormone, T4, and 10% is the active hormone T3. The T4 hormone makes its way around the body, where it is then converted to either the bioactive T3 or the less active Reverse T3 (rT3) in the cells of the liver, kidney, brain and skeletal muscle.

T3 is the power horse of the thyroid hormones and is responsible for entering the nucleus of the cells and executing the thyroid hormone’s downstream effects. T3 thyroid hormone has profound physiological effects in the body and affects everything…

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 The Thyroid Hormone System

The Principal Function of the Thyroid Hormones- "spark" for the oxidative reactions and regulation of metabolic rates in the body. T3 is ten times more active than T4. T3 also acts two to three times faster than T4. T3 is the tissue active form of the thyroid hormone.

Articles of Interest

Background on Thyroid Hormones: T0, T1, T2, T3, T4

T4 is inert too, but conversion to T3 (in the liver, kidneys, brain, and other organs) activates it, in a highly regulated way. Taking T3 (or using Armour thyroid) bypasses that natural regulation, which is generally an unhelpful thing to do. Consequently, pure T4 is normally the best, most stable, and most reliable form of thyroid hormone replacement.

Chemistry of Thyroid Hormones

A large majority of the thyroid hormone secreted from the thyroid gland is T4, but T3 is the considerably more active hormone. Although some T3 is also secreted, the bulk of the T3 is derived by deiodination of T4 in peripheral tissues, especially liver and kidney. Deiodination of T4 also yields reverse T3, a molecule with no known metabolic activity.

Discovery illuminates how thyroid hormone 'dims' metabolism

It has been known for some time that the thyroid gland is a strong regulator of the body's metabolism, making it key to many health conditions. But the molecular details of how thyroid hormone acts on cells in the body have never been fully understood.

For Thyroid Hormones, How Low Is Too Low?

But just what is "normal" is "an incredibly controversial question," said Dr. David Cooper, director of the endocrinology division at Sinai Hospital in Baltimore and a professor at Johns Hopkins School of Medicine.

How reliable are free thyroid and total T3 hormone assays?

The two major thyroid hormones produced by the thyroid gland are 3,5,3′-triiodothyronine (T3) and thyroxine (T4). The thyroid gland exclusively synthesizes T4, and produces approximately 20% of T3. The majority of T3 is generated by 5′-deiodination catalyzed by type I and type II T4–5′-deiodinases in peripheral tissue.

How Thyroid Hormones Interact

T3 and T4 are the hormones that are necessary to sustain life. If either of them is out of balance it can wreak havoc on health.

Mechanisms of thyroid hormone action

Our understanding of thyroid hormone action has been substantially altered by recent clinical observations of thyroid signaling defects in syndromes of hormone resistance and in a broad range of conditions, including profound mental retardation, obesity, metabolic disorders, and a number of cancers.

Restoring Thyroid Hormone Balance

The thyroid gland plays a major role in the regulation of many body processes, especially those related to metabolic function. Maintaining optimal function of the thyroid and balanced levels of its main hormones, triiodothyronine (T3) and thyroxine (T4), is vital for overall health. Dysfunction of thyroid hormone performance is quite common and may result from conditions such as thyroiditis and hypothyroidism.

Reverse T3 or perverse T3? Still puzzling after 40 years

Four decades after reverse T3 (3,3′5′-triiodothyronine) was discovered, its physiologic and clinical relevance remains unclear and is still being studied. But scientific uncertainty has not stopped writers in the consumer press and on the Internet from making unsubstantiated claims about this hormone. Many patients believe their hypothyroid symptoms are due to high levels of reverse T3 and want to be tested for it, and some even bring in test results from independent laboratories.

The Use of L-T4 + L-T3 in the Treatment of Hypothyroidism

Every experienced clinician knows that there are some patients with L-T4-treated hypothyroidism who do not recover completely [9]. Dissatisfaction with outcome of L-T4 monotherapy is often expressed on websites of thyroid patient associations. There are, however, just a few controlled studies which have evaluated dissatisfaction and remaining complaints in a quantitative manner.

Thyroid Hormone - Everything You Need To Know

It’s the little butterfly-shaped thyroid gland located in your neck, which could be causing you trouble. The thyroid hormones produced by the thyroid gland support nearly every cell in your body.

Thyroid Hormone Regulation of Metabolism

An improved understanding of the mechanism underlying the actions of TH on lipid metabolism and thermogenesis has led to several useful compounds targeting TR for treatment of metabolic disorders.

Thyroid hormones, T3 and T4, in the brain

Of the two major THs, T4 (3,5,3′,5′-tetraiodo-l-thyronine) is classically viewed as an pro-hormone that must be converted to T3 (3,5,3′-tri-iodo-l-thyronine) via tissue-level deiodinases for biological activity. THs primarily mediate their effects by binding to thyroid hormone receptor (TR) isoforms, predominantly TRα1 and TRβ1, which are expressed in different tissues and exhibit distinctive roles in endocrinology.

Thyroid test and its significance (t3 & t4)

Thyroid hormones are primarily found in a bound form, and a tiny portion, 0.03% of T4 and 0.3% of T3 travel freely (FT3 & FT4) in the blood and have hormonal activity. Moreover, T3 is produced by conversion from T4 in the body.

Thyrotropin-Releasing Hormone and the Thyroid Hormone Feedback Mechanism

Thyroid hormone (TH) plays a critical role in development, growth, and cellular metabolism. TH production is controlled by a complex mechanism of positive and negative regulation. Hypothalamic TSH-releasing hormone (TRH) stimulates TSH secretion from the anterior pituitary. TSH then initiates TH synthesis and release from the thyroid gland.

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 are T3, T4, and TSH?

Thyroxine (T4) is responsible for your metabolism, mood, and body temperature, among other things. T3, too, is made in the thyroid gland, and it can also be made in other tissues within the body by converting T4 (in a process called deiodination) into T3. This hormone is at the center of your digestive and metabolic function, and it also oversees bone health.

What is T4 and T3? A Simple Guide For The Non-Scientist

Interestingly, thyroid hormones are the only compounds in the body that contain iodine. This is why dietary intake of iodine is important for thyroid health. T4 is produced by the thyroid gland in much greater amounts than T3, around 90% more. This is because when T4 reaches organs and body tissue, it’s converted into T3.

Resources

Endocrine Society

The thyroid gland releases triiodothyronine (T3) and thyroxine (T4). These hormones play an important role in regulation of your weight, energy levels, internal temperature, skin, hair, nail growth, metabolism and is an important part of the endocrine system.

StatPearls

The thyroid hormone is well known for controlling metabolism, growth, and many other bodily functions. The thyroid gland, anterior pituitary gland, and hypothalamus comprise a self-regulatory circuit called the hypothalamic-pituitary-thyroid axis. The main hormones produced by the thyroid gland are thyroxine or tetraiodothyronine (T4) and triiodothyronine (T3).