What is hypothyroidism?

Hypothyroidism (underactive thyroid) is when the thyroid gland produces insufficient thyroid hormone to meet the needs of the body. The thyroid gland is a butterfly shaped gland in the lower front of the neck. It has important functions in the body: thyroid hormones are essential for the function of all cells, growth and regulating our metabolism. If thyroid hormone levels are low, many of the body’s functions slow down.




What are the symptoms of hypothyroidism?

Low levels of thyroid hormone results in slowing down of the mental and physical processes of the whole body. Some people with mild hypothyroidism have no symptoms. Fatigue and weight gain may be attributed to getting older. However, as your metabolism continues to slow you may develop more obvious symptoms which include:

  • Weight gain 
  • Lack of energy
  • Cold intolerance
  • Thin and brittle hair
  • Muscle pains
  • Hoarse voice
  • Puffy face
  • Constipation
  • In women – irregular menses, heavy periods, difficulty conceiving
  • Goitre, or an enlarged thyroid gland

If left untreated hypothyroidism can slow the heart and make you feel tired or out of breath when you exercise. It can also increase the risk of obesity, high cholesterol levels and heart disease.


What are the causes of hypothyroidism?

Hashimoto’s thyroiditis. This is the most common cause and is an autoimmune disease. The body’s immune system attacks of thyroid cells, rendering them inactive. We are not sure why this happens, but it is likely to be a combination of factors, such as your genes and an environmental trigger.

Other common causes include:

  • Thyroiditis, or inflammation of the thyroid gland, usually developing following a viral infection or pregnancy. Thyroiditis is often self-limiting many patients will be able to come off medication after a few months of treatment.
  • Following treatment for hyperthyroidism with  radioactive iodine or surgery
  • Medications such as lithium and amiodarone 


How is hypothyroidism diagnosed?

The thyroid gland produces two hormones: triiodothyronine (T3) and thyroxine (T4) and is controlled by thyroid-stimulating hormone (TSH). About 80% of the hormone produced is T4 which is converted in the cells into T3, the active thyroid hormone. TSH is produced by the pituitary gland, a tiny gland located in the brain, and stimulates the thyroid gland to release thyroid hormone.

Hypothyroidism is diagnosed by a blood test to measure thyroid hormones. TSH levels that are above normal and T4 levels that are below normal may mean you have hypothyroidism.

  • Your doctor will arrange a blood test to measure your thyroid function
  • If this is abnormal they will also measure your thyroid autoantibodies and may do a few other blood tests
  • If your thyroid gland is enlarged your doctor may also arrange a thyroid ultrasound


How is hypothyroidism treated?

  • Hypothyroidism cannot be cured but it can be completely controlled. It is treated by replacing the amount of hormone that your own thyroid can no longer make to bring your thyroid function levels back to normal. 
  • Treatment for hypothyroidism involves taking the thyroid hormone pill, levothyroxine every day. 
  • You should take levothyroxine on an empty stomach first thing in the morning with some water at least 30 minutes before any food or drink.
  • Thyroxine has negligible side effects when taken in the correct dose. Once treatment has started your symptoms will improve over a few weeks. You will need regular appointments with your doctor to check your thyroid function and adjust the dose of your medication accordingly.
  • Levothyroxine comes under different generic or brand names. Even though they all work equally well, you should not switch between the pills as this can cause levels of thyroid hormone to fluctuate.
  • You will need to have your thyroid function checked 4-8 weeks after any thyroxine dose change, more frequently if you are pregnant.


What if I want to conceive?

Most women with controlled hypothyroidism have healthy pregnancies. It is important to plan the pregnancy and ensure your thyroid function is normal when you conceive to minimise any risks to yourself or the baby. Left untreated, hypothyroidism increases the risk of miscarriage, premature delivery and can also seriously affect the developing baby.

For the first half of pregnancy, the baby is completely dependent on the mother for the production of thyroid hormone and so your thyroxine dose requirements usually increase. Your doctor will therefore probably increase the dose of thyroxine once you conceive.

During pregnancy, your thyroid hormone levels are usually checked every 4 weeks and your dose of thyroxine dose adjusted as necessary. 

As soon as you have delivered  most women go back to their prepregnancy dose of thyroxine.