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Thyroid disease: causes, symptoms, and risk factors

Your guide to thyroid disease, conditions and how to test thyroid health.

Thyroid disease is common, yet many symptoms of thyroid disease can be hard to diagnose.

To help you better understand thyroid and thyroid-related diseases, we explore what the thyroid does and the causes, symptoms, and risk factors of the most common thyroid conditions.

What is the thyroid?

The thyroid is a small butterfly-shaped gland that sits at the front of the neck, either side of the windpipe or trachea. It consists of two lobes that are connected by a small tissue bridge called the isthmus.

What does the thyroid do?

The thyroid is part of the endocrine system and produces hormones that affect almost every cell in the body. Without thyroid hormones, the body would be unable to convert nutrients into energy.

The two main thyroid hormones are:

  • Thyroxine (T4) – relatively inactive

  • Triiodothyronine (T3) - highly biologically active

Why are thyroid hormones important?

The thyroid hormones T4 and T3 are vital in regulating metabolism. They control the speed of the cells in your body, in turn governing how fast your heart beats and how quickly your intestines process food. That’s why symptoms of a thyroid-related condition include feeling tired all the time or experiencing changes in mood, weight, or energy levels.

The thyroid produces a greater amount of T4 than T3 because the cells and tissues in the body, particularly the liver, convert T4 into the more active T3. The majority of T4 and T3 hormones that circulate in the blood are bound to proteins, and cannot be used by cells, while a smaller proportion remains free and unbound.

When looking into a thyroid condition, it is usually the levels of free hormones that are tested – free T3 (FT3) and free T4 (FT4) as it is a more useful measure of the amount of hormone that is free and available for use by the cells.

What controls the thyroid?

A feedback loop system involving the hypothalamus in the brain and the pituitary and thyroid glands controls the production and release of thyroid hormones.

If thyroid hormone levels in the blood are low, the hypothalamus produces thyroid releasing hormone (TRH). TRH instructs the pituitary gland to produce thyroid-stimulating hormone (TSH), which leads to an increase in T4 and T3 production by the thyroid.

Levels of TSH continually rise and fall, depending on the level of thyroid hormones circulating in the blood. High TSH levels stimulate the thyroid to produce more thyroid hormones, while low levels of TSH cause the thyroid to decrease hormone production.

What is thyroid disease?

Thyroid disease is where a medical condition is keeping your thyroid from making the right level of hormones.

Thyroid diseases include:

  • An overactive or underactive thyroid
  • An autoimmune disease
  • Thyroid swelling
  • Nodules
  • Cancer

As many as one in 20 people have a thyroid disorder, which may be temporary or permanent [1].

Hypothyroidism (an underactive thyroid)

An underactive thyroid is where the thyroid gland does not produce enough T4 and T3 hormones to maintain a healthy metabolic rate. Low thyroid hormone levels ultimately lead to the metabolism slowing down.

Hyperthyroidism (an overactive thyroid)

With an overactive thyroid, also known as hyperthyroidism, the thyroid makes too much T4 and T3. An excess of thyroid hormones speeds up the metabolism.

Autoimmune disease

Thyroid conditions are often the result of autoimmune disease where healthy tissue in the body is attacked by the immune system.

Hashimoto's disease is the most common cause of hypothyroidism. In Hashimoto's disease, the immune system produces antibodies that target and destroy the thyroid gland, eventually leading to a decrease in thyroid hormone production.

Graves' disease is the most common cause of hyperthyroidism. In Graves' disease, the immune system creates antibodies that target the thyroid and increase the production of both T3 and T4.

The risk of Hashimoto’s or Graves' disease increases if you have a family history of autoimmune disease.

Thyroid swelling or goitre

A goitre is a swelling and inflammation of the thyroid gland, causing a lump in the front of the neck. Occasionally, a goitre may cause a tight feeling in your throat and lead to difficulty swallowing and breathing.

Causes of a goitre:

  • Underactive or overactive thyroid
  • Low iodine in the diet
  • Certain medications such as lithium
  • Radiation to the head or neck
  • Thyroid cancer


Nodules are singular or multiple lumps within the thyroid gland. Although usually harmless, nodules on the thyroid should be looked at by a doctor to see whether they need to be treated or removed.

Thyroid cancer

Thyroid cancer is a rare form of cancer in the UK and is more common in women than men. Survival rates for thyroid cancer are relatively high and, once detected, the thyroid gland can be removed and followed by hormone therapy. Radioactive iodine therapy is effective at killing thyroid cancer cells. Each year, about 3,400 people in the UK are diagnosed with thyroid cancer [2].

If you are having treatment for thyroid cancer and would like to talk to someone, organisations like Macmillan can support you. You can choose to chat with a Macmillan specialist online or call 0808 808 00 00.

Symptoms of thyroid disease

Symptoms of thyroid disorders can be debilitating but are often difficult to diagnose. Many symptoms can be overlooked, especially if they are mild, or confused with other conditions.

Once you’ve read through the symptoms of thyroid disease, have a look at how to diagnose and manage a thyroid condition.

Symptoms of an underactive thyroid

An underactive thyroid (hypothyroidism) is associated with the metabolism slowing down.

Symptoms of an underactive thyroid:

  • Extreme fatigue
  • Weight gain and difficulty losing weight
  • Feeling cold all the time (cold hands and feet)
  • Breathlessness
  • Slow heartbeat
  • Insomnia
  • Loss of libido
  • Hair loss (especially the outer third of eyebrows)
  • Dry hair and skin
  • Brittle nails
  • Irregular and heavy periods
  • Depression
  • Mood swings
  • Brain fog
  • Fertility problems
  • Goitre

Symptoms of an overactive thyroid

With an overactive thyroid (hyperthyroidism), the metabolism speeds up.

Symptoms of an overactive thyroid:

  • Feeling hyperactive
  • Weight loss despite
  • Increased appetite
  • Feeling warm and sweating excessively
  • Warm, clammy skin
  • Shortness of breath
  • Rapid heartbeat
  • Insomnia
  • Raised libido
  • Osteoporosis
  • Thin fly-away hair
  • Thin itchy skin
  • Thickened nails
  • Frequent bowel movements and diarrhoea
  • Light, scanty periods
  • Tremor and shakiness
  • Gritty, protruding eyes
  • Irritability
  • Fertility problems
  • Goitre

Thyroid disease risk factors

Anyone can develop a thyroid disorder, but several factors can increase the risk of developing thyroid disease.

Being female

Women are at greater risk of developing a thyroid disorder than men, which may be linked to the prevalence of autoimmune diseases in women. Nearly 80% of people with autoimmune disorders are women, and Hashimoto's and Graves' disease are leading causes of thyroid conditions.

Female hormones can influence the development of a thyroid disorder. Oestrogen, a hormone abundant in the first half of a menstrual cycle, can enhance the inflammatory process of the immune system and contribute to thyroid attack. The pregnancy-related hormone, human chorionic gonadotropin (hCG), can also affect thyroid hormone levels in the blood during pregnancy. A small number of women develop postpartum thyroiditis up to a year after they have given birth. This is associated with women who have thyroid antibodies but may not yet have developed thyroid disease.

Being over the age of 50

Getting older increases the prevalence of thyroid disorders in both men and women. Many people over the age of 50 have thyroid-related symptoms but go undiagnosed or are misdiagnosed because their symptoms are often blamed on getting older.

A family history of thyroid problems

Having a family history of thyroid disease increases the risk of developing a thyroid condition. A family history of autoimmune disease can slightly increase the risk of developing an autoimmune thyroid disease such as Hashimoto's disease or Graves' disease.

Radiation exposure

Exposing the neck to radiation during medical treatments for neck and head cancer increases the risk of developing autoimmune thyroid disease and thyroid cancer [3]. In some medical tests, an iodine-based contrast agent is used, and this can slightly increase the risk of developing temporary thyroiditis or thyroid problems.


Certain medications like amiodarone, interferon-alpha, interleukin-2 and lithium can affect the production of thyroid hormones.


Smoking increases the risk of developing autoimmune thyroid diseases. Cigarettes contain a chemical called thiocyanate, which is an anti-thyroid agent and affects the production of thyroid hormones.

Low iodine intake

Dietary iodine is important for thyroid health as the thyroid uses it to produce T4 and T3. The only way to get iodine is through diet because the body can't produce it.

Iodine can be found in iodised salt, seafood, bread, and milk. Low iodine levels can lead to a decrease in the levels of thyroid hormones produced. High levels can lead to either hypothyroidism or hyperthyroidism.

Have a look at our thyroid-friendly diet guide.