Thyroid Hormone

Thyroid hormones

Your thyroid makes 2 main hormones: triiodothyronine (T3) and thyroxine (T4). Adequate amounts of iodine (a chemical element that is an essential part of our diet) are needed for the thyroid to produce these hormones. Another hormone that is produced in the thyroid gland is called calcitonin. This hormone, secreted by a small population of cells known as C cells, is involved in regulating the level of calcium and phosphate in the blood.

The main thyroid hormones are secreted directly into the bloodstream and go to all parts of the body. Most of the T4 is converted to T3 (the active form of the hormone) in your organs and tissues. Thyroid hormones affect your body’s metabolic rate and regulate many of your bodily functions, including breathing, heart rate, body temperature, digestion, and how quickly you burn calories.

The amount of hormones the thyroid produces is usually tightly regulated. A part of your brain called the hypothalamus tells your pituitary gland (an important gland in your brain) to make a hormone called thyroid-stimulating hormone (TSH). TSH then tells your thyroid to make T3 and T4. The level of thyroid hormones in your body then feeds back to the hypothalamus and pituitary gland, which in turn adjust the release of TSH.

What causes thyroid problems?

Thyroid dysfunction is when too much or not enough thyroid hormones are produced. It can be caused by:

  • primary thyroid disorders: problems with the thyroid gland itself; or
  • central thyroid disorders: problems with the pituitary gland (secondary disorders) or the hypothalamus (tertiary disorders).

While inadequate iodine intake is the most common cause of thyroid disease worldwide, autoimmune problems (where your immune system produces antibodies that attack the thyroid gland) are the most common cause of thyroid problems in Australia. Sometimes thyroid problems start during or after pregnancy.


Hyperthyroidism occurs when there is an overproduction of thyroid hormones. It can result in symptoms such as:

  • weight loss despite normal or increased appetite and food intake;
  • fast or irregular heartbeat, which can cause palpitations;
  • feeling short of breath;
  • often feeling hot or increased sensitivity to heat;
  • perspiration;
  • feeling jumpy, anxious, or nervous;
  • sleeping problems;
  • tremor (shaking), which often affects the hands;
  • Diarrhoea;
  • tiredness;
  • muscular weakness; and
  • Skin and hair changes: thinning of the skin and hair that becomes brittle.

In women, irregular periods are a common symptom.

Causes of hyperthyroidism

Graves’ disease, an autoimmune condition, is the most common cause of hyperthyroidism in Australia. In Grave’s disease, antibodies made by your immune system stimulate your thyroid to make too much thyroxine. It can cause inflammation of the thyroid (goitre) and thyroid eye disease. It usually affects people between the ages of 20 and 60 and is much more common in women than in men.

Other common causes of hyperthyroidism include the following:

  • Toxic thyroid nodule or toxic multinodular goitre: Conditions in which noncancerous growths develop on the thyroid and produce excessive amounts of thyroxine.
  • Thyroiditis (inflammation of the thyroid), can cause temporary hyperthyroidism because the inflamed thyroid releases its stores of thyroxine into the bloodstream. Thyroiditis can occur due to an autoimmune problem, after pregnancy, or after a viral infection. Thyroiditis is sometimes painful.


Hypothyroidism is when you have an underactive thyroid. Symptoms usually develop gradually, sometimes over several years, and may include:

  • weight gain;
  • tiredness;
  • feeling cold all the time, or sensitivity to cold;
  • constipation;
  • Dry Skin;
  • ‘swollen face;
  • hair loss or hair thinning;
  • hoarsely;
  • memory problems;
  • feeling depressed;
  • joint and muscle pain and/or stiffness;
  • muscular weakness; and
  • slow heartbeat (pulse).

Women with hypothyroidism may notice an irregular or heavy periods.

Causes of hypothyroidism

Hashimoto’s thyroiditis (also called Hashimoto’s disease), an autoimmune condition, is the most common cause of hypothyroidism. Thyroid damage from radiation therapy used to treat head or neck cancers or certain medications (eg, lithium, amiodarone, interferon alfa) can also cause hypothyroidism. And sometimes treatment for an overactive thyroid can sadly end.

Who has thyroid problems?

  • Both underactive and overactive thyroid conditions are more common in women than men.
  • Hypothyroidism is more common in people over 55 years of age.
  • If you have a family history of thyroid problems or have an autoimmune disease, you’re also at higher risk.


Untreated thyroid disorders can lead to other problems, such as heart disease, high cholesterol, high blood pressure, and osteoporosis.

Diagnosis and tests

If you’ve noticed any swelling in your neck or notice symptoms of an overactive or underactive thyroid, talk to your doctor. If your GP (general practitioner) suspects that you have a thyroid problem, he or she will ask about your symptoms and perform a physical exam, including an exam of your neck. Both hyperthyroidism and hypothyroidism can be associated with a generalized inflammation of the thyroid, known as a goitre. Thyroid nodules (noncancerous lumps) and thyroid cancer can appear as firm, usually painless lumps on the thyroid.

Simple blood tests can be done to assess thyroid function and help determine the cause of your thyroid problem. Sometimes scans of the thyroid gland may also be needed to diagnose thyroid disease. Your doctor may refer you to an endocrinologist (a doctor who specializes in treating hormonal conditions such as thyroid disease) or a thyroid surgeon for further testing and treatment.

Thyroid antibody tests

Blood tests for thyroid antibodies can help determine the cause of your thyroid problem. The presence of antibodies against the TSH receptor (TRAb) indicates Graves’ disease. Thyroid peroxidase antibodies (TPOAb) can be increased in people with Grave’s disease or Hashimoto’s thyroiditis, as well as other autoimmune thyroid problems.

Thyroid scans

Thyroid nuclear medicine scans can help determine the cause of hyperthyroidism (overactive thyroid). A radionuclide thyroid scan can show whether the entire thyroid or a nodule (or nodules) within the thyroid is overactive. You are injected with a small amount of radioactive substance and then scanned to observe the uptake of the “tracer” by your thyroid. The scans can show the structure and function of your thyroid gland.

An ultrasound may be needed if there is swelling of the thyroid or a lump. Ultrasounds can show whether a lump is cystic (fluid-filled) or solid. Brain scans may be recommended if problems with the pituitary gland are thought to be causing thyroid dysfunction.

Treatment of hyperthyroidism

Treatment for hyperthyroidism depends on the cause. Other factors, such as your age and general health, and the severity of your hyperthyroidism will also help determine the best treatment for you.

Graves’ disease is usually treated with drugs that suppress the formation of T3 and T4. Carbimazole (brand name Neo-Mercazole) is the antithyroid drug usually prescribed, but propylthiouracil (PTU tablets) may be used in some circumstances. Radioactive iodine (which shrinks the thyroid gland) or surgery (removal of all or most of the gland) are other treatment options that may also be recommended.

Toxic multinodular goitre and toxic adenomas are usually treated with surgery or radioactive iodine. Antithyroid medications may also be recommended.

Thyroiditis often does not need specific treatment, but beta-blocker medications and pain relievers can be given to treat symptoms.

Subclinical hyperthyroidism often improves without treatment, but follow-up thyroid function tests are recommended.

Many people who are treated for hyperthyroidism develop hypothyroidism, either right away or over time. Long-term monitoring with thyroid function tests is recommended for all people with thyroid disorders.

Hypothyroidism treatments

Treatment for hypothyroidism involves taking thyroxine, usually levothyroxine tablets (brand names include Eltroxin, Eutroxsig, and Oroxine). Thyroxine replacement aims to return thyroid hormone levels to normal and relieve symptoms. It may take a few months to get the right dose for you; Thyroid function tests should be done every 4 to 8 weeks when you start treatment to guide dosage. Most people with hypothyroidism will need lifelong treatment with levothyroxine and ongoing monitoring of their thyroid function.

Treatment of subclinical hypothyroidism will depend on your symptoms (or lack of symptoms), TSH level, age, and general health. Thyroxine tablets may be recommended for some people, while for others continuous monitoring of thyroid function may be all that is needed. Some studies have found that taking selenium supplements improves the quality of life in certain people with Hashimoto’s thyroiditis.