What is the thyroid and what does it do?

The thyroid is an endocrine gland. These are a group of glands that release hormones into the circulatory system.

The thyroid makes two hormones which regulate the body’s metabolism, heart rate and temperature. These hormones are called thyroxine (T3) and triiodothyronine (T4).

The thyroid is located at the front of your neck just below the Adam’s apple. It is made up of a right and left lobe either side of the wind-pipe, which are joined by a bridge of tissue called the isthmus. In order to function properly, the thyroid needs to receive a sufficient amount of iodine.

(We consume this in our diet. Fish is quite high in iodine, and it’s also present in some soil grown vegetables.)

T3 and T4 regulate the speed at which the body’s cells and organs work. The thyroid gland also produces calcitonin. This helps to regulate the levels of calcium and phosphate in the blood.

What conditions can develop due to problems with the thyroid?

Hypothyroidism and hyperthyroidism are the most common. Even though they sound similar, they refer to different conditions.


If the thyroid produces too many hormones, this can lead to hyperthyroidism, or overactive thyroid. This then means that certain organ functions, such as heart rate, can speed up.

Hyperthyroidism can cause symptoms such as:

  • weight loss
  • anxiety
  • heat intolerance
  • mood swings
  • insomnia
  • tiredness
  • swelling of the thyroid gland, or goitre
  • palpitations
  • or shivering

People who notice the above symptoms should see their GP for advice. If they suspect that an overactive thyroid could be a possible cause, then they will organise a blood test to check it.

More tests may then be required to see what is causing it.

Autoimmune thyroid disease, or Graves' disease, is the cause of hyperthyroidism in around three quarters of cases. This is where the immune system attacks the thyroid gland, and then the thyroid produces too much hormone.

Nodules on the thyroid can also cause hyperthyroidism, as can certain medications.


Conversely, if the thyroid doesn’t produce enough T3 and T4, this is known as hypothyroidism, or underactive thyroid. Not producing enough of these hormones can cause organ function to slow down. This might mean that the digestive system doesn’t metabolise food as quickly, or that heart rate is lower.

Symptoms include:

  • tiredness
  • feeling cold
  • weight gain
  • poor concentration
  • dry skin
  • or aching muscles.

Again, it’s important to talk to a doctor if you notice any of the above. A blood test can determine how well the thyroid is functioning. If it isn’t working in the way it should, more tests may be recommended to see why.

Like hyperthyroidism, many cases are autoimmune; where the bodies defences mistakenly attack the gland. But unlike in hyperthyroidism, this inhibits production of T3 and T4 (rather than accelerates it).

One autoimmune disorder which can lead to underactive thyroid is Hashimoto’s disease.

In other cases, hypothyroidism may come about as a result of treatment for an overactive thyroid, or thyroid cancer.


This is characterised by inflammation of the thyroid.

There are several types of thyroiditis, including:

  • Viral or subacute thyroiditis. This is caused by a viral infection of the gland and is associated with flu-like symptoms.
  • Postpartum thyroiditis. This is thyroiditis which occurs in the first 6 months after pregnancy.
  • Autoimmune thyroiditis. Where the body attacks the thyroid cells as if they were foreign.

Other conditions

  • Thyroid eye disease. This can happen as a result of autoimmune hyperthyroidism, where the eye tissue and muscle becomes inflamed. This leads to pressure pushing the eyes forward to the front of the sockets.
  • Thyroid cancer. A rare condition where cancerous cells develop in the thyroid. Symptoms include hoarseness and a sore throat that doesn’t improve over a period of weeks, and problems swallowing. If a goitre (neck swelling) develops very rapidly, this can in rare cases be a sign of thyroid cancer; however in most cases swellings in the thyroid are benign.
  • Nodules or swellings. Nodules are lumps on the thyroid gland. These can sometimes cause a goitre.

How are thyroid conditions diagnosed?

Thyroid conditions can be diagnosed by taking a blood sample to check T3 and T4 levels.

A doctor may also examine the neck to check for swelling, and imaging tests (such as a CT scan, MRI or ultrasound) can be used to check for thyroid enlargement.

A radioactive iodine test can be used to show the uptake of radioactive iodine by normal thyroid tissue. The areas where this occurs are called hot nodules.

Fine needle aspiration can also be used to extract some sample cells from the thyroid for analysis.

In terms of treatment, there are various medications that can be prescribed to adjust hormone levels.

What does treatment involve?

It depends on the condition affecting the thyroid, and how severely affected thyroid levels are. In some cases, treatment may not be necessary.

Where treatment is recommended, in hyperthyroidism this might be:

  • a group of antithyroid medications called thianomides are usually prescribed. These include carbimazole and methimazole, which stop the thyroid from producing excess amounts of T4 and T3 hormones.
  • radioiodine treatment is another treatment for overactive thyroid. The iodine in the pill gradually shrinks the thyroid which reduces its activity.
  • In some cases, where the above do not have the desired effect, part or all of the thyroid may be removed via surgery. This is called a thyroidectomy.

In hypothyroidism this might be:

  • hormone replacement therapy. Levothyroxine may be prescribed to raise thyroxine levels. In many cases, this may be taken long term.

In thyroid cancer, the most common treatments are:

  • surgery
  • radioactive iodine treatment (which kills cancerous cells)
  • radiotherapy
  • or chemotherapy

The treatments issued for thyroiditis can vary, depending on the cause. In viral cases, for instance, hormone levels may return to normal after a few weeks. But if hormone levels continue to be low, replacement therapy may be advised.