Underactive thyroid

What is hypothyroidism?

Hypothyroidism is a hormone deficiency in which the thyroid gland does not produce enough of the hormone Thyroxine. This hormone is used to regulate metabolism.

An underactive thyroid is more common in people aged between 40 and 50, and affects 10 times more women than men. It's estimated that 1 in 1,000 men have hypothyroidism, while the condition is much more prevalent in women, affecting 10 in 1,000 women.

What is the thyroid?

The thyroid gland is a butterfly shaped organ located at the base of the neck in front of the trachea (windpipe). It is made up of two lobes (the butterflies wings) which are connected by a piece of tissue called the isthmus (the butterflies body)

The thyroid converts iodine from our diets into two hormones called tri-iodothyronine (T3) and thyroxine (T4). These hormones are secreted straight into the bloodstream and are used to regulate many vital body functions including body temperature, cholesterol levels, breathing, body mass, heart rate and menstrual cycles.

Three glands are responsible for the regulation of T3 and T4 levels in the blood. These glands are called the hypothalamus, pituitary gland and the thyroid gland.

The hypothalamus in the brain monitors the level of hormones in the blood. If not enough of the hormones are present in the blood, the hypothalamus releases thyrotropin-releasing hormones (TRH).

The TRH instructs the pituitary gland to produce more thyroid-stimulating hormone (TSH), which promotes the thyroid gland to produce more T3 and T4 hormones.

If one of these three glands fails to function, hypothyroidism can develop. There are three types of hypothyroidism:

• Primary hypothyroidism - This is when the thyroid does not produce enough T3 and T4 hormones
• Secondary hypothyroidism - This is when the pituitary gland fails to produce TSH, resulting in lower levels of T3 and T4 in the blood
• Tertiary hypothyroidism - This is when the hypothalamus fails to produce TRH. This condition is also known as euthyroid sick syndrome or Pickardt-Fahlbusch syndrome.

What causes an underactive thyroid

The most common cause of hypothyroidism is an autoimmune disorder called Hashimoto's thyroiditis. This autoimmune disease causes the body's immune system to attack the thyroid, damaging the cells and reducing the thyroids' ability to produce T3 and T4 hormones.

Another common cause of an underactive thyroid is over-response or over-use of treatments for hyperthyroidism, or overactive thyroid. These treatments are used to lower the amount of thyroxine and tri-iodothyronine. However, they can cause the levels to drop too low, resulting in hypothyroidism.

Surgery, such as a thyroidectomy, can cause a drop in thyroid activity. Thyroidectomy is the surgical removal of all or part of the thyroid. It is performed for thyroid cancer, goiter and hyperthyroidism.

What are the symptoms of an underactive thyroid?

Symptoms of an underactive thyroid can be easily misinterpreted as a number of other conditions. It can take a long time for symptoms to develop, which means you may not realise you have a problem for many years. If you are concerned that you may have an underactive thyroid, speak to your GP about getting tested for an underactive thyroid.

Symptoms include:

• Being sensitive to cold
• Depression
• Dry skin and hair
• Muscle aches
• Tiredness
• Weight gain

How is an underactive thyroid diagnosed?

To determine whether a person has hypothyroidism, a thyroid function test is required. A sample of blood is taken, from which the hormone levels are tested.

You should speak to your GP about being tested for an underactive thyroid if you are concerned.

In the UK, all babies are screened for congenital hypothyroidism during the early stages of their development.

What treatments are available for an underactive thyroid?

Typically, hypothyroidism is treated with daily hormone replacement tablets. These tablets increase the levels of thyroxine in your body.

Levothyroxine tablets are often prescribed to increase the levels of thyroxine in the blood. This helps to regulate the bodies metabolic rate which, over time, reduces the symptoms of hypothyroidism.

This treatment is lifelong, but shouldn't stop you living a normal and healthy life.

If left untreated, an underactive thyroid can develop into the following symptoms:

• Anaemia (iron deficiency)
• Hearing loss
• Increased risk of heart disease
• Lower-pitched and hoarse voice
• Puffed up face
• Slow heart rate
• Thinning or partly missing eyebrows

Table of contents

What is an underactive thyroid?

What is the thyroid?

What causes an underactive thyroid?

What are the symptoms of an underactive thyroid?

How is an underactive thyroid diagnosed?

What treatments are available for an underactive thyroid?