Your thyroid gland produces hormones that help control your metabolism. If you don’t make enough of these hormones it’s called hypothyroidism. If you make too much of these hormones it’s called hyperthyroidism. If your thyroid isn't working properly it can cause tiredness, weight gain or loss, and mood problems.

What is the thyroid gland?

Your thyroid gland is a gland found at the front of your neck, just below your Adam’s apple. It makes up a part of your endocrine system. Your endocrine system is made up of all of the glands (special groups of cells) in your body. These glands produce hormones — “chemical messengers” that travel in your blood to tissues and organs around your body.

Your thyroid gland uses iodine to make two hormones that help control your metabolism:

  • thyroxine (T4) — 4 iodine molecules
  • triiodothyronine (T3) — 3 iodine molecules

Your hypothalamus (part of your brain) and pituitary gland (a gland at the base of your brain) regulate the levels of these hormones. If your T3 and T4 levels drop, your hypothalamus releases thyrotropin-releasing hormone (TRH). This stimulates your pituitary gland to produce another hormone called thyroid-stimulating hormone (TSH). TSH then stimulates your thyroid gland to produce more T3 and T4.

You can check your thyroid health at home with a thyroid blood test.

Thyroid butterfly-shaped gland

What do thyroid hormones do?

T3 is the only hormone that your body can actually use, so your body must first convert T4 to T3. An enzyme called deiodinase does this by removing one iodine molecule.

T3 helps control your body’s metabolism — the chemical processes that occur in your body that keep you alive, like breathing and breaking down food into energy.

Thyroid disorders

Sometimes, your thyroid gland might produce too much or too little T3 and T4. If you don’t produce enough it’s called hypothyroidism (an underactive thyroid) and if you produce too much it’s called hyperthyroidism (an overactive thyroid).

Complications of thyroid disorders

It’s important to test your thyroid if you think you might suffer from a thyroid disorder.

If left untreated, an underactive thyroid can cause:

  • elevated cholesterol — increasing your risk of heart attack and stroke
  • goitre — swelling of your thyroid gland which causes a lump in the front of your neck
  • myxoedema coma — a rare life-threatening where thyroid hormone levels become very low
  • dementia

If left untreated, an overactive thyroid can cause:

  • eye problems — like sensitivity to the light, watery eyes, double vision, and damage to the surface of the eye
  • atrial fibrillation — a heart condition that causes an abnormal heart rhythm
  • heart failure
  • osteoporosis — thinning of the bones which increases the risk of bone fractures
  • thyroid storm — a rare life-threatening condition that causes a rapid heartbeat, fever, vomiting, and confusion

Thyroid disorders are also associated with pregnancy complications, like miscarriage, premature birth, and pre-eclampsia.

Testing for thyroid disorders

You can check for a thyroid disorder with a blood test.

A basic test will check your thyroid hormone levels, which can diagnose an underactive or overactive thyroid. A more advanced test will also check for thyroid antibodies, called thyroid peroxidase antibody (TPO) and thyroglobulin antibody (TGAb). These antibodies are what cause autoimmune thyroid diseases.

Treating thyroid disorders

An underactive thyroid is usually treated with a medication called levothyroxine — a hormone replacement tablet.

An overactive thyroid is usually treated with either medication, radiation, or surgery.

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References

American Thyroid Association and American Association of Clinical Endocrinologists Taskforce on Hyperthyroidism and Other Causes of Thyrotoxicosis, Bahn, R. S., Burch, H. B., Cooper, D. S., Garber, J. R., Greenlee, M. C., ... & Rivkees, S. A. (2011). Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. Thyroid, 21(6), 593-646.

Abalovich, M., Amino, N., Barbour, L. A., Cobin, R. H., De Groot, L. J., Glinoer, D., ... & Stagnaro-Green, A. (2007). Management of thyroid dysfunction during pregnancy and postpartum: an Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology & Metabolism, 92(8_supplement), s1-s7.

Casey, B. M., Dashe, J. S., Wells, C. E., McIntire, D. D., Byrd, W., Leveno, K. J., & Cunningham, F. G. (2005). Subclinical hypothyroidism and pregnancy outcomes. Obstetrics & Gynecology, 105(2), 239-245.

Garber, J. R., Cobin, R. H., Gharib, H., Hennessey, J. V., Klein, I., Mechanick, J. I., ... & Woeber for the American Association of Clinical Endocrinologists and American Thyroid Association Taskforce on Hypothyroidism in Adults, K. A. (2012). Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Thyroid, 22(12), 1200-1235.