Thursday, April 11, 2024

T3 And T4 Thyroid Hormones

The More Medication Myth

T4 and T3 Thyroid Hormones Explained

You may have heard that thyroid hormones can be used to lose weight, even in people without thyroid disease. While synthetic thyroid hormones have been used this way in the past, research has shown that most people gain all the weight back once they stop using them. Worse, being on thyroid hormones unnecessarily can result in serious side effects.

For people who are already using levothyroxine, increasing the dose above whats needed can lead to more weight loss, but its usually not significant and those pounds are often gained back once the dose is decreased again.

This is also an unhealthy way to lose weight, as an increased dose is also associated with adverse reactions, including heart issues, insomnia, headaches, menstrual irregularities, and skin rash.

What Is A T4 Test

T4 Tests A Total T4 test measures the bound and free thyroxine hormone in the blood. A Free T4 measures what is not bound and able to freely enter and affect the body tissues.

What does it mean if T4 levels are abnormal? Importantly, Total T4 levels are affected by medications and medical conditions that change thyroid hormone binding proteins. Estrogen, oral contraceptive pills, pregnancy, liver disease, and hepatitis C virus infection are common causes of increased thyroid hormone binding proteins and will result in a high Total T4. Testosterone or androgens and anabolic steroids are common causes of thyroid hormone binding proteins and will result in a low Total T4.

In some circumstances, like pregnancy, a person may have normal thyroid function but Total T4 levels outside of the normal reference range. Tests measuring free T4 either a free T4 or free T4 index may more accurately reflect how the thyroid gland is functioning in these circumstances. An endocrinologist can determine when thyroid disease is present in the context of abnormal thyroid binding proteins.

What Are Typical Symptoms Of Hyper

Typical symptoms for hyperthyroidism is weight loss, fast heart rate, high irritability/nervousness, muscle weakness and tremors, infrequent menstrual periods, sleep problems, eye irritations and heat sensitivity.

Symptoms for hypothyroidism is the contrary of hyperthyroidism such as weight gain, slower heart rate, fatigue, more frequent and stronger menstrual periods, forgetfulness, dry skin and hair, hoarse voice and intolerance to cold. In addition, hypothyroidism is often accompanied by an enlargement of the thyroid gland known as goitre.

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Thyroid And Parathyroid Hormones

The thyroid gland releases triiodothyronine and thyroxine . 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.

Although it gets less attention than thyroid hormones, the parathyroid hormone is still important in the body. Parathyroid hormone is connected to blood calcium levels in the bones, intestines and kidneys. Parathyroid hormone comes from four parathyroid glands in the neck, just behind the thyroid. These glands receive feedback from blood calcium levels to determine when they need to secrete the hormone. The hormone plays a role in regulating blood calcium levels, helping the body maintain adequate calcium stores in the bloodstream to protect bone health.

What can go wrong with calcitonin?

What is T4?

Thyroxine is produced by the thyroid gland under regulation from the hypothalamus and pituitary gland. The feedback loop signals to the hypothalamus in to release thyrotropin-releasing hormone, which then stimulates the pituitary gland to release the thyroid stimulating hormone.

What is T3?

T3 is a second thyroid hormone that is produced by the thyroid gland, but also in other tissues through deiodination of T4. T3 helps maintain muscle control, brain function and development, heart and digestive functions. It also plays a role in the bodys metabolic rate and the maintenance of bone health.

Problems Associated with T3 and T4?

What Is T3 Uptake

Molecules of Thyroid Hormones T3 and T4 Stock Illustration ...

Sometimes, you may hear doctors talking about T3 uptake when discussing thyroid testing. What is T3 uptake? The book Clinical Methods says that T3RU test measures the levels of proteins in the blood that carry thyroid hormone.7 T3 uptake can help your doctor interpret the results of T3 and T4 blood tests. The T3RU test is hardly used these days because the TBG and the free T4 blood tests are now available.

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T4 Converts To T3 In The Tissues

T3 is the active thyroid hormone, responsible for all of the biological actions of the thyroid hormone. Daily total production of T3 is about 32 micrograms , about 75-80% of which comes from T4 to T3 conversion in the peripheral tissues. However, about 20-25% of the total daily production of T3 comes directly from the thyroid gland.

T4 to T3 conversion takes place under the guidance of an enzyme called 5-deiodinase . There are two types of 5-DI: Type 1-DI and Type 2-DI.

Type 1-DI is most abundant in the peripheral tissues, especially in the thyroid, liver, kidneys, and muscles. Type 2-DI is mostly found in the brain and pituitary gland.

What Are T3 And T: The Complete Guide To Your Thyroid Hormones

Jenny Hills, Nutritionist and Medical Writer Health

T3 and T4 are hormones that are secreted by your thyroid gland and have a major impact on your health. T4 is the thyroid hormone thyroxine and T3 is the hormone triiodothyronine, and they affect almost every organ in your body. T4 and T3 levels in your body are regulated by the thyroid-stimulating hormone, or TSH for short. Thyroid tests to check thyroid function usually check for abnormal levels of TSH and T4 hormones.

Symptoms of hypothyroidism are usually associated with low levels of T4 and T3. This can cause you to feel fatigued, have difficulty losing weight, feel tired, and have hair loss. An underactive thyroid is also associated with high TSH levels and low T4 levels.

An overactive thyroid or hyperthyroidism is caused by high T4 and T3 levels in your bloodstream. When your thyroid secretes too much thyroid hormones you can feel restless, suffer from sleep problems, have frequent digestive upset, and increased sweating. If you suffer from hyperthyroidism, your thyroid test results will usually show low levels of TSH hormone.

This article contains a complete guide to your thyroid hormones and thyroid function. You will learn what T4 and T3 hormones do in your body and what the target range of T3 and T4 is. I will also explore why testing for free T4 levels is sometimes better than a TSH blood test.

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What Are T3 And T4

T3 is the thyroid hormone triiodothyronine and T4 is the thyroid hormone thyroxine.

The British Thyroid Foundation says that T3 and T4 are the two main hormones that your thyroid gland secretes. Together they affect and influence almost every cell in your body. Your thyroid usually produces more T4 hormone than T3, but T4 is converted to T3 when it reaches cells and tissues in your body. Therefore, T4 is the more important hormone to measure when testing for thyroid dysfunction.4

Lets look in more detail at what T3 does and why T4 is the more potent hormone.

Difference Between T3 And T4 Thyroid Hormones

Thyroid Gland and Hormones

As thyroid hormones, T3 and T4 play crucial roles in metabolism and digestive functions. However, they have several differences warranting independent monitoring when it comes to secretion quantity to detect hypothyroidism or hyperthyroidism.

For one, 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.

Did You Know? Aside from T3 and T4, its important to assess your thyroid-stimulating hormone or thyrotropin. TSH stimulates the secretion of thyroid hormones. Therefore, abnormal T3 and T4 can be traced back to TSH production problems in the brains pituitary gland.

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How Tsh Is Connected With T3 And T4 Levels

Dr. Oliver Starr on explains that all your thyroid hormones and TSH need to work in balance. This forms what doctors call a feedback loop where the levels of thyroid hormone in your blood signal to your brain to produce more or less TSH.17

For example, if an overactive thyroid produces too much T4 or T3, the feedback loop to your brain signals to produce less TSH. The same is true if your thyroid isnt working properly and produces too little hormone.

Doctors from the National Health Service explain the basic relationship between TSH and thyroid hormone levels:18

  • Hypothyroidism: TSH high, T4 low, and T3 low or normal
  • Hyperthyroidism: TSH low, T4 high or normal, and T3 high or normal
  • Subclinical thyroid disease: Levels of T4 and T3 are normal but TSH is either too high or too low
  • Non-thyroidal illness: TSH low, T4 low or normal, and T3 low or normal

Medically Approved By Dr Edward Salko Md

Dr. Edward Salko is the board-certified physician who reviews lab tests provided by PERSONALABS. He earned his Bachelor of Science in chemistry and pre-med from the University of Florida in Gainesville and his Doctor of Osteopathy Medicine in 1980 from Kansas City University School of Medicine.

Dr. Salkos career has specialized in family and emergency medicine. His passion is to provide clients with the tools they need in the most convenient way possible to allow them to take charge of their own healthcare. He has held a variety of positions in Kansas, Florida and Washington. Currently, in addition to his duties as Medical Director for Personalabs, he is a practicing emergency physician in Kennewick, Washington.

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What Is Thyroid Hormone

Thyroid hormone is the hormone thats mainly responsible for controlling the speed of your bodys metabolism. In infants, thyroid hormone is critical for brain development. Your thyroid, a small, butterfly-shaped gland located at the front of your neck under your skin, makes and releases thyroid hormone. Its a part of your endocrine system.

Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, muscles and other tissues. These signals tell your body what to do and when to do it.

Metabolism is the complex process of how your body transforms the food you consume into energy. All of the cells in your body need energy to function.

Thyroid hormone actually represents the combination of the two main hormones that your thyroid gland releases: thyroxine and triiodothyronine . Theyre often collectively referred to as thyroid hormone because T4 is largely inactive, meaning it doesnt impact your cells, whereas T3 is active. Once your thyroid releases T4, certain organs in your body transform it into T3 so that it can impact your cells and your metabolism.

Your thyroid also releases a hormone called calcitonin to help regulate calcium levels in your blood by decreasing it. Calcitonin isnt grouped into the thyroid hormone name, and it doesnt impact your bodys metabolism like T3 and T4 do.

What Is Free T4

Molecules of Thyroid Hormones T3 and T4 Stock Illustration ...

Similar to free T3, free thyroxine levels are the unbound levels of T4 hormone . You have more free T4 in your blood than FT3. High T4 levels or low T4 levels can help to accurately diagnose hyperthyroidism or hypothyroidism. The book Clinical Methods says that blood tests for both TSH and T4 help to accurately assess thyroid health.7

The amount of free T4 helps doctors see how much thyroid gland hormone is available in your blood to meet your energy requirements.

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The Role Of Thyroid Hormones

Thyroid hormones heavily influence your metabolism, your body temperature, and your appetite regulation. Your thyroid works closely with your hypothalamus, a small area of your brain, to maintain both your weight and your energy balancewhats left after you eat and your body uses the calories it needs.

How this happens isnt exactly clear, but one thing is certain: It isnt thyroid hormones alone that play a role in how much energy your body uses. Thyroid hormones work along with a number of other hormones, proteins, nuclear receptors, and chemicals, which is why its such a complicated process.

Weight Loss With Treatment

There arent many scientific studies regarding how much weight is gained or lost once hypothyroid people are treated with the synthetic thyroid hormone levothyroxine, but the limited evidence that is available indicates that not everyone loses weight with treatment and in the ones who do, its limited.

Once your hormone levels are within the normal range, you may lose a small amount of weight that mainly consists of the extra water and salt your body has built up. However, weight gain has multiple factors, and yours is more than likely not all due to your thyroids slowdown. One way to tell is if treatment has helped all of your other thyroid symptoms, but not your weight. This indicates that your thyroid very likely isnt the only factor behind your gain.

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What Is A T3 Test

T3 Tests T3 tests measure triiodothyronine levels in the blood. A Total T3 test measures the bound and free fractions of triiodothyronine. Hyperthyroid patients typically have an elevated Total T3 level. T3 tests can be used to support a diagnosis of hyperthyroidism and can determine the severity hyperthyroidism.

In some thyroid diseases, the proportions of T3 and T4 in the blood change and can provide diagnostic information. A pattern of increased T3 vs T4 is characteristic of Graves disease. On the other hand, medications like steroids and amiodarone, and severe illness can decrease the amount of thyroid hormone the body converts from T4 to T3 resulting in a lower proportion of T3.

T3 levels fall late in the course of hypothyroidism and therefore are not routinely used to evaluate patients with underactive or surgically absent thyroid glands.

Measurement of Free T3 is possible, but is often not reliable and therefore may not be helpful.

What Is A Tsh Test

Thyroid Hormone T4 T3 Synthesis| USMLE STEP NCLEX COMLEX

Thyroid tests Blood tests to measure thyroid hormones are readily available and widely used. Not all thyroid tests are useful in all situations.

TSH Test The best way to initially test thyroid function is to measure the TSH level in a blood sample. Changes in TSH can serve as an “early warning system” often occurring before the actual level of thyroid hormones in the body becomes too high or too low.

A high TSH level indicates that the thyroid gland is not making enough thyroid hormone . On the other hand, a low TSH level usually indicates that the thyroid is producing too much thyroid hormone . Occasionally, a low TSH may result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid . In most healthy individuals, a normal TSH value means that the thyroid is functioning properly.

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Thyroxine Iodine And Apoptosis

Thyroxine and iodine stimulate the spectacular apoptosis of the cells of the larval gills, tail and fins in amphibian metamorphosis, and stimulate the evolution of their nervous system transforming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog. In fact, amphibian frog Xenopus laevis serves as an ideal model system for the study of the mechanisms of apoptosis.

When Should I See My Doctor About My Thyroid Hormone Levels

Abnormal thyroid hormone levels usually cause noticeable symptoms. Since thyroid hormone is responsible for controlling the speed of your metabolism, too much thyroid hormone can make it faster than normal and too little thyroid hormone can slow it down. These imbalances cause certain symptoms, including:

  • Unexplained weight gain or weight loss.
  • Slow or fast heart rate.
  • Intolerance to cold or heat.
  • Dry or moist skin.

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What Causes Thyroid Disease

There are various different factors causing hyper- and hypothyroidism.

The following conditions cause hypothyroidism:

Thyroiditis is an inflammation of the thyroid gland. This can lower the number of hormones produced.

A special form of thyroiditis is Hashimoto’s thyroiditis. This is a genetic disorder caused by diseases of the immune system and can be passed from one generation to the other. In addition, thyroiditis can occur in women after giving birth also referred to as postpartum thyroiditis. It is usually a temporary condition and occurs only in 5-9% of woman giving birth.

Nutrition also impacts your thyroid functions. Iodine deficiency can cause hypothyroidism. This is a worldwide problem affecting approximately 100 million people. As mentioned earlier, iodine is used by the thyroid gland to produce hormones.

The following conditions cause hyperthyroidism:

Graves’ disease is a condition where the entire thyroid gland might be overactive and produce too much hormone. Your thyroid gland might be enlarged. This problem is also called diffuse toxic goitre.

Thyroiditis can also cause the opposite and trigger the release of hormones that were stored in the thyroid gland. This uncontrolled release of thyroid hormones causes hyperthyroidism for a few weeks or months. It may occur in women after childbirth.

How Does The Thyroid Gland Function

What Is The Difference Between T3 And T4 In Thyroid Function?

The major thyroid hormone secreted by the thyroid gland is thyroxine, also called T4 because it contains four iodine atoms. To exert its effects, T4 is converted to triiodothyronine by the removal of an iodine atom. This occurs mainly in the liver and in certain tissues where T3 acts, such as in the brain. The amount of T4 produced by the thyroid gland is controlled by another hormone, which is made in the pituitary gland located at the base of the brain, called thyroid stimulating hormone . The amount of TSH that the pituitary sends into the bloodstream depends on the amount of T4 that the pituitary sees. If the pituitary sees very little T4, then it produces more TSH to tell the thyroid gland to produce more T4. Once the T4 in the bloodstream goes above a certain level, the pituitarys production of TSH is shut off. In fact, the thyroid and pituitary act in many ways like a heater and a thermostat. When the heater is off and it becomes cold, the thermostat reads the temperature and turns on the heater. When the heat rises to an appropriate level, the thermostat senses this and turns off the heater. Thus, the thyroid and the pituitary, like a heater and thermostat, turn on and off. This is illustrated in the figure below.

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