What are Thyroid hormones?

Triiodothyronine (T3) and Thyroxine (T4) are tyrosine-based hormones produced by the thyroid gland which are secreted into the blood and then supplied to every tissue in the body.

What are the functions of Thyroid hormones? (General)
  • Regulation of metabolism
  • Aid the body to use energy and stay warm
  • Maintain the brain, heart, muscles and other organs.
Brief functions of Triiodothyronine (T3)
  • Regulation of growth and development
  • Helps to control metabolism and body temperature
  • Acts to inhibit the secretion of thyrotropin (A hormone that regulates the production of thyroid hormones) by the pituitary gland (a negative-feedback system)
  • Acts as the most active thyroid hormone and affects all body processes, including gene expressions.
Brief functions of Thyroxine (T4)

Plays at least some role in controlling basal metabolic rate (BMR), energy production, the cardiovascular system, bone health, the central nervous system, the reproductive system, growth and development, and the digestive system.

What is BMR?

  • BMR (basal metabolic rate) is the rate at which energy is used by an organism at complete rest or simply the amount of energy required by the body in a day.
  • It is measured in humans by the heat given off per unit time, and expressed as the calories released per kilogram of body weight OR per square meter of body surface per hour.

How does Thyroxine aids in controlling the BMR rate?

  • Thyroxine controls the speed of metabolism and the amount of energy released. Inside each cell are tiny energy-producing organelles called mitochondria. Thyroxine controls BMR by increasing the concentration of mitochondria in a cell and by increasing the energy produced by mitochondria

How does Thyroxine produce energy?

  • It controls lipid, carbohydrate, and protein metabolism.
  • It accelerates the conversion of fat cells into fatty acids and glycerol which can be used as energy in the body.

Metabolism of carbohydrates results in a supply of powerful, quick-acting energy for the body.


A TSH (Thyroid Stimulating Hormone) Test is performed to assess the activity of the thyroid gland. It involves measuring the concentration of thyroid-stimulating hormone (TSH) in the blood serum.

A change in the level of TSH in the blood may signify a malfunctioning of the thyroid gland. When T3 and T4 are too high, TSH secretion decreases, when T3 and T4 are low, TSH secretion increases.

TSH T3 T4 Interpretation
High Normal Normal Mild Hypothyroidism
High Low/Normal Low Hypothyroidism
Low Normal Normal Mild Hypothyroidism
Low High / Normal high / Normal Hypothyroidism
Low Low / Normal Low / Normal Non-thyroidal illness or rare pituitary hypothyroidism

High TSH levels indicate that the thyroid is underactive, and a low TSH means the thyroid is overactive. Abnormal TSH levels alert medical professionals to diseases of the thyroid gland.

The American Thyroid Association (ATA) recommends adults begin screening for thyroid dysfunction at age 35.

What are the two main functional disorders of the thyroid gland?
    Hypothyroidism (due to a poorly functioning thyroid gland) Hyperthyroidism (caused by an overactive thyroid gland).
    Other non-functional disorders (where the thyroid hormone levels are normal) are
    • Goiters : Refers to the enlargement of the thyroid gland and is not cancerous. A person with goiter can have normal levels of thyroid hormone (euthyroidism), excessive levels (hyperthyroidism) or levels that are too low (hypothyroidism).
    • Nodules : Refers to any abnormal growth that forms a lump in the thyroid gland.(either benign or cancerous)
    What is Hypothyroidism?

    Hypothyroidism due to an under-active or poorly functioning thyroid gland is a very common thyroid disorder.

    What happens during hypothyroidism?

    This under-production of the hormones (T3 and T4) slows down the body's metabolism, often leaving patients feeling cold, tired, and depressed.

    What are the symptoms of hypothyroidism?

    Symptoms of hypothyroidism vary from person to person but are non-specific and common to many other conditions, meaning the correct diagnosis can easily be missed.

    • Weight gain despite a sensible diet and exercise.
    • High cholesterol levels.
    • Fatigue, cold and heat intolerance.
    • Hypotension (abnormal low blood pressure)
    • Fluid retention (failure to eliminate fluids from the body)
    • Dry, flaky, pale skin.
    • Thin and brittle hair
    • Increased hair loss or brittle
    • Cracked fingernails
    • Puffy face, hands and feet.
    • Constipation
    • Headaches/drowsiness
    • Irregular menstrual periods in females
    • Pre-menstrual syndrome (PMS) (a condition characterized by affective, behavioral and somatic symptoms during the luteal phase of the menstrual cycle, resolved with onset of menstruation. PMS affects 10-30% of menstruating women)
    • Low sexual desires
    • Infertility
    • Aching muscles and joints
    • Depression, anxiety
    • Slowed metabolism
    • Decreased heart rate
    • Memory impairment
    • Enlarged tongue
    • Deep voice
    • Swollen neck

    Yet, more than half of all people with thyroid disease are unaware of their condition.

    What are the potential causes of hypothyroidism?
    • Iodine deficiency : Iodine is essential for the production of thyroid hormones, and iodine deficiency is a superior cause of congenital hypothyroidism worldwide. Iodine deficiency also results in an enlargement of the thyroid gland (goiter).
    • Congenital Hypothyroidism : Infants can be born with a thyroid gland which is not well formed or even without one.
    • Autoimmune thyroiditis : A chronic inflammatory disorder of the thyroid gland that is caused by abnormal blood antibodies and white blood cells that mistakenly attack and damage healthy thyroid cells.
    • Surgical removal of the thyroid gland.

      The surgery is performed if you have any of the following:

      1. A small thyroid growth (nodule or cyst)

      2. A thyroid gland that is so overactive and dangerous (thyrotoxicosis)

      3. Cancer of the thyroid

      4. Noncancerous (benign) tumors of the thyroid that are causing symptoms

      5. Thyroid swelling (nontoxic goiter) that makes it hard for you to breathe or swallow

      6. Refuse to undergo radioactive iodine treatment when you have an overactive thyroid gland.

      7. Couldn't be treated with antithyroid medicines.

    • Drugs : Certain medicines include amiodarone, used to treat an abnormal heart rhythm, and lithium, used in psychiatric patients may cause hypothyroidism.
    Who are the ones at greater risk of hypothyroidism?
    • Females : Those who are pregnant, during the immediate post-delivery period, and after the menopause.
    • People with a family history of autoimmune thyroiditis or suffering from any other autoimmune diseases such as type 1 diabetes.
    • Those aged over 50 years.
    • Patients who have undergone thyroid surgery.
    • Those with Down's or Turner's syndrome.
    • Patients treated with radioiodine (radioactive iodine). This is usually for hyperthyroidism (overactive thyroid gland).
    • People with exposure of the neck to x-ray or radiation treatment (usually for cancer).
    • Caucasians and Asians are at greater risk due to genetic factors.
    • Patients with pre-eclampsia (severe hypertension during pregnancy).(proven after 2009)

    The physical symptoms of hypothyroidism are displeasing and can affect the victim's self-confidence, career, and family life. However, hypothyroidism does not only fade away a patient's quality of life, if untreated, it can cause serious and difficult situations to handle.

    Hypothyroidism can lead to
    • Body functions to slow down so much that patients may slip into a coma (myxoedema coma)
    • High blood pressure and elevated cholesterol levels leading to heart attacks and strokes
    • Heart failure
    • Infertility
    • Alzheimer's disease (increased risk in females)

    Treatment for hypothyroidism is by replacing the thyroid hormones, which the thyroid gland normally makes. As there is no cure for hypothyroidism, patients will need to take their medication for the rest of their lives. Fortunately, once on replacement therapy, they will be able to lead normal lives. For example, a young woman will be able to conceive and bear children.

    What is thyroid hormone therapy?

    Thyroid hormone therapy is the use of synthetic thyroid hormones to raise abnormally low levels of thyroid hormones. Often used to treat an underactive thyroid that is secreting little or no thyroid hormones, thyroid hormone therapy is usually administered in pill form.

    Who needs thyroid hormone therapy?

    Thyroid hormone therapy is generally prescribed when a person's thyroid is not producing enough thyroid hormone naturally (a condition referred to as hypothyroidism). Other reasons for using thyroid hormone therapy may include

    • To control the growth of the enlarged thyroid gland (also called goiter)
    • To control the growth of nodules on the thyroid gland
    • If there is a history of thyroid cancer (use of thyroid hormone therapy can reduce the risk of recurring tumors)
    • To control levels of thyroid stimulating hormones (TSH), which may stimulate thyroid cancer
    How is thyroid hormone therapy dosage determined?

    Proper dosage is tailored to each individual patient's needs through careful blood testing. The blood tests reveal levels of thyroid hormones in the blood, as well as thyroid stimulating hormones (TSH) emitted by the pituitary gland. The pituitary gland plays an integral role in the functioning of the thyroid gland. It controls how much thyroid hormone is released by producing TSH that "stimulates" the thyroid. Increased levels of TSH may indicate an underactive thyroid.

    Yearly checkups are usually conducted to measure levels of thyroid hormones and TSH. Hypothyroidism can be a progressive disease, requiring dosage increases over time.

    Ensuring proper thyroid hormone dosage

    Proper thyroid hormone dosage is based on blood tests that measure levels of thyroid hormone and thyroid-stimulating hormone (TSH). However, to ensure proper dosage for the duration of the treatment, consider the following recommendations

    • Maintain regular visits to your physician.
    • Take your thyroid medication daily.
    • Notify your physician of your thyroid hormone treatment before beginning treatment for any other disease, as some adjunctive treatments can affect the dosage of thyroid hormone therapy.
    • Let your physician know if you become pregnant.
    • Notify your physician of any new symptoms that may arise.
    • Notify all healthcare providers of your thyroid condition and medication dosage.
    Available Formulation
    • Vegetable Capsule T3:T4 [a combination of both Thyronine (T3) and Thyroxine (T4)]
    Why choose a combination therapy of T3:T4 compared to monotherapy of either T3 or T4?

    Normal thyroid gland makes two thyroid hormones, 100 T4 and 20 T3 per day, per 70kg body weight. In our body, most of the T4 are converted to T3. So, T3 is the active hormone; in fact, more than 80% of the T3 in our blood is made from T4 which has been changed by the liver and other tissues outside the thyroid. Underactive thyroids still make both T4 and T3 but insufficient. Because the failing thyroid still makes some T3, and because body tissues turn some T4 into T3, most hypothyroid patients do not need to take much T3 instead pay more concentration on T4. In fact, most patients do not feel completely normal on T4 alone.

    Moreover, through a clinical study organized by the European Journal of Endocrinology, it is found out that, when patients are given T4 as monotherapy, it is assumed that the peripheral conversion from T4 into T3 provides sufficient T3 for the peripheral tissues.

    However, the intracellular concentration of deiodinase (enzyme that is involved in the activation or deactivation of thyroid hormones) and the cellular uptake of T3 are not equal in all tissues.

    Additionally, studies in hypothyroid rats suggest that it is only possible to reach an optimal thyroid hormone therapy (euthyroidism) using a combination of T3and T4. In patients in whom long-term T4 therapy was substituted by the equivalent combination of T3 and T4 scored better in a variety of neuropsychological tests. (Endocrine Clinic, Royal Infirmary, Edinburgh, UK)

    A T4-T3 combination might also help people who have had their whole thyroid removed and can't make any T4 or T3 of their own.

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