Thyroxine

Thyroxine






Thyroxine is the name of the hormone secreted by thyroid gland which does the work of metabolic activities. It also controls the rate of oxidation level in the cells. Thyroxine hormone contains 65% iodine which is necessary for the production of T3 and T4 (tyrosine) hormones. When there is deficiency of iodine it will automatically reduce the production of T3 and T4 hormones causing Goiter. When there is increase in thyroxine this leads to a condition called hyperthyroidism.

Hence the thyroxine hormone should be at the optimal level for normal health.

Function :

Thyroid hormone is responsible for circulating the protein content in the blood. Most of the hormones will contain certain amount of protein and only some of them are free circulating still biologically active.

Hence thyroxine carries out the job of plasma transport to all the cells in your body. Thyroid hormone cannot get through cell membranes like that of lipophilic substances.

The primary function of thyroxine is to control the metabolic rate in our body. It helps to regulate the bone growth in combination with growth hormone. It further acts to increase the body’s sensitivity towards catecholamine.

Thyroid hormone is absolutely necessary for normal development of cells and they are vital in controlling the metabolism of proteins and fats in your body. In addition, it also controls various physiological activities and help in heat generation in the body.

In animals, thyroxine is responsible for hibernation period and it controls the molting behavior in birds.

Excess of Thyroxine :

In one deciliter of blood, there should be 4.5—11.2 mcg of thyroxine in blood. This is considered as standard level of this hormone and anything lesser than and higher than this normal level is dangerous.

When thyroxine level crosses the limit and circulates in excess, this condition is called hyperthyroidism (Grave’s disease). Similarly, when the level is below 4.5 then this condition is called Hypothyroidism, which arises due to deficiency of thyroxine. People with low level of thyroxine will have dry skin with white patches, slow reflexes, slow pulse rate, enlarged heart and slow speech. Goiter is a condition of low thyroxine level in blood and such people will have rapid weight gain, weakness, joint pain and stiffness in joints. They will also have symptoms of difficulty in concentration, loss of memory and Sleeping Sickness. They are more prone to Heart Attack and Stroke than normal individuals.

In hyperthyroidism, the thyroxine per deciliter crosses the normal range which may cause serious health complications. People with excess of thyroxine will have germ cell tumors, Grave’s disease, and trophoblastic disease. They would sweat a lot on the entire body and their skin will be moist almost all the time. Further their nails will be rising up in the edges signifying Plummer’s nail condition. Their pulse rate will be very high with increased palpitation.

Treatment :

Doctors would administer T3 and T4 hormones to treat deficiency of thyroxine. Levothyroxine is the medicine given for treating hypothyroidism.

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Thyroxine – Function, Levels, Side Effects, Dosage, Weight loss

Thyroxine – Function, Levels, Side Effects, Dosage, Weight Loss

What is Thyroxine?

Thyroxine or Tetraiodothyronine (T4) is one of the three major hormones secreted by the thyroid gland. Thyroxine, in particular, is produced by the follicular cells of the thyroid gland.

Thyroxine Function

The hormone thyroxine is very important in the body’s metabolic function because it has effects in the functions of the different organs of the body.

• In the liver, the hormone functions to increase glucose synthesis to pyruvate, conversion of fats to sugar, and hastens the release of cholesterol.


• In the digestive system, thyroxine functions to increase the secretion of the digestive juices and promotes smooth muscle function and thus facilitate contractions for gastric motility.


• In the skeletal and cardiac muscles, thyroxine also plays a major role in their functions. This hormone helps in the normal development of the human body as well as tone and function.


• In the bones, thyroxine promotes bone maturation as the person age.


• The hormone thyroxine also plays an important role in the normal development of the body systems during younger age and maintains its function throughout adulthood.


• The reproductive system also benefits so much of this hormone. It increases the possibility of childbearing and promotes the secretion of milk by the breasts.


• Thyroxine also plays an important role in the skin as it increases hydration, secretions of exocrine glands, hair growth.

Thyroxine Levels

The levels of the hormone thyroxine can be tested through the thyroxine test. There have been two ways of testing the thyroxine levels in the body: the total T4 test and the free T4 test. The former has been used for so many years in the diagnosis of hyperthyroidism and Hypothyroidism, but it is said that total T4 tests can be affected by the level of proteins. On the other hand, free T4 test, which is a newer test, is not affected by the level of proteins. Free T4 is the active form of thyroxine; therefore, it is regarded by many as the accurate representation of thyroxine function. However, whichever of the two tests is needed, it is always done after or at the same time a TSH test is performed. The purpose of these tests is to determine whether the hormone’s feedback system is intact. Thus, a T4 and TSH tests is one strong combination of tests in establishing diagnosis in cases affecting the thyroxine levels.

Side Effects of Thyroxine

Thyroxine when used is considered to be a hormone replacement therapy. If the level used exceeds the needed amount will result to increased metabolic activity and lead to the following:

• Palpitations


• Chest pain


• Muscle cramps


• Sweating


• Tremors


• Diarrhea


• Restlessness


• Insomnia and Headache

The reassuring thing about this situation, though, is that symptoms will usually respond to reduction in the dosage. There are also effects when thyroxine is used in conjunction with other medications. If the hormone is used in patients with diabetes, it is said that the need for insulin will most likely increase.

Thyroxine and Weight Loss

Thyroxine is considered to be a one of the hormones that synthesizes fats. Thyroxine increases the metabolism so if one is undergoing thyroxine replacement therapy, one feels more energetic, will burn more calories, and eventually, experience weight loss. Here’s another way how thyroxine contributes in losing weight.

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• It increases energy expenditure since the hormone makes the cells use up more energy.


• Exercise is the most practical and easy way to increase the thyroid levels. Doing exercise will stimulate the production of thyroxine by the thyroid glands.


• A healthy liver will have a great effect in the release of thyroxine by the thyroid gland. The liver is the main gland that stimulates the thyroid gland in producing the right amount of thyroxine needed by the body.

Thyroxine Dosage

The half-life of the hormone thyroxine runs for 7–10 days although it has much longer biological effect. The dosage will depend on body weight and age. Therefore, dosage will vary between children and adult. Children require larger doses of thyroxine compared to adults wherein the latter require about 1.6 microgram/kg/day2. Thus, adults will maintain level of 100–200 microgram/day to reach a safe level. In addition, the thyroxine level required in the elderly might also decline.

How to start thyroxine therapy?

The introduction of thyroxine therapy should be based on how long the hypothyroidism had existed and identify the health risks the patient may have such as coronary heart disease or heart failure. However, if a patient is otherwise healthy and has very minimal risks factors, then he or she can immediately undergo the therapy maintaining the level of 100–200 microgram/day.

For elderly patients and with identified heart disease can have a daily dose of 25 microgram for 3–4 weeks and should be reassessed before further increase of dosage to 25 microgram for 3–4 weeks until the predicted dose will be achieved. If the patient’s coronary symptoms are getting worse, manage and control the symptoms first before increasing the dosage and if a cardiac disease is strongly established, thyroxine dosage should be reduced.

For patients classified within these two, then it is safer to let them start a dosage of 50 micrograms/day and can be increased after 3–4 weeks.