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Thyroid Health Guide

Your everyday doesn’t have to be so tiring. Checking your thyroid could hold the answers to better skin, losing weight and regaining your energy. 

SHOP THYROID HEALTH TESTS Dr Sam Rodgers - Chief Medical Officer

Reviewed by Dr Sam Rodgers

9th October 2019


Butterfly Icon with Chapter One

Chapter 1

What is the thyroid?

Butterfly Icon to show Chapter 2

Chapter 2

What is thyroid disease (and who is at risk)?

Buttonfly icon showing chapter 3

Chapter 3

What are the symptoms of thyroid disease?

Diagnosing and managing a thyroid condition

Chapter 4

Diagnosing and managing a thyroid condition

How often should I take a thyroid function test?

Chapter 5

How often should I take a thyroid function test?

Underactive thyroid diagnosis and treatment

Chapter 6

Underactive thyroid diagnosis and treatment

Overactive thyroid diagnosis and treatment

Chapter 7

Overactive thyroid diagnosis and treatment

Glossary of thyroid terms

Chapter 8

Glossary of thyroid terms

Ultrasound scan of human thyroid gland

Chapter 1

What is the thyroid?

If your thyroid doesn’t function properly it can have debilitating effects.  Here we take a look at this important hormone-producing gland.

The thyroid is a butterfly-shaped gland consisting of two lobes, located either side of the windpipe at the front of the neck, and connected by a small tissue bridge called the isthmus. It is part of the body’s endocrine (hormone-producing) system and produces important 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) – which is inactive – and triiodothyronine (T3), which is biologically active.

Why are thyroid hormones important?

The thyroid hormones T4 and T3 are vital in regulating metabolism. They control the speed at which the cells in your body work, in turn governing how fast your heart beats and how quickly your intestines process food. The thyroid produces a greater amount of T4 than T3. This is because the cells and tissues in the body (particularly the liver) convert T4 into the active T3. The majority of T4 and T3 hormones that circulate in the blood are bound to proteins, and therefore cannot be used by cells, while a smaller a proportion remains free and unbound. When investigating a thyroid condition, it is usually the levels of free hormones that are tested – free T3 (FT3) and free T4 (FT4) – because this 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 TSH Releasing Hormone (TRH). TRH instructs the pituitary gland to produce thyroid stimulating hormone (TSH), which in turn 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.

Five women in winer coats walking arm in arm down street

Chapter 2

What is thyroid disease (and who is at risk)?

As many as 1 in 20 people are thought to have a thyroid disorder. Below, we explore the different thyroid conditions and the key risk factors you should be looking for.

Thyroid disorders are very common and there are a number of different conditions that can affect the normal functioning of the thyroid.

Hypothyroidism (an underactive thyroid)

With an underactive thyroid, also known as hypothyroidism, the thyroid gland does not produce enough of the hormones T4 and T3 to maintain a healthy metabolic rate. Low thyroid hormone levels ultimately lead to a slowing down of the body's metabolism.

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 metabolism in the body.

Autoimmune disease

Thyroid conditions are often the result of an autoimmune disorder, where healthy tissue in the body is attacked by the immune system. Hashimoto's disease is an autoimmune disorder and is the most common cause of hypothyroidism. In Hashimoto's disease, the body's immune system produces antibodies that target and destroy the thyroid gland, eventually leading to a decrease in thyroid hormone production. Graves' disease is another autoimmune disease that affects the thyroid and is the most common cause of hyperthyroidism. In Graves' disease, the body's 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 is raised if you have a family history of autoimmune disease.

Thyroid swelling or a "goitre"

A goitre is a swelling and inflammation of the thyroid gland causing a lump in the front of the neck. Usually, the swelling does not cause any symptoms, but occasionally a goitre may cause a tight feeling in your throat and lead to difficulty in swallowing and breathing.

There can be many possible causes of a goitre:

  • Both an underactive and overactive thyroid may lead to the development of a goitre
  • Low iodine in the diet
  • Certain medications such as lithium
  • Medical treatment that exposes the head or neck to radiation
  • Thyroid cancer


Nodules are lumps within the thyroid gland and an individual may have a single nodule or multiple nodules. Although usually harmless, they should be examined 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 in 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.

Key risk factors

Although anyone can develop a thyroid disorder, there are a number of different factors that can increase an individual's risk of developing thyroid disease.

Being female

Women are at greater risk of developing a thyroid disorder than men. Although the reason why is not yet fully understood, it is probably linked to the prevalence of autoimmune disease in women. Nearly 80% of people who have autoimmune disorders are women, and Hashimoto's and Graves' disease (both autoimmune disorders) are leading causes of thyroid conditions.

Female hormones can also influence the development of a thyroid disorder. Oestrogen, a hormone abundant in the first half of a woman's 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

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


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


Smoking can increase the risk of developing autoimmune thyroid disease. Cigarettes contain a chemical called thiocyanate, which is an antithyroid agent and affects the production of thyroid hormones.

Low iodine intake

Dietary iodine is very important for thyroid health as it is used by the thyroid to produce both T4 and T3. Iodine is obtained through the diet as the body can't produce it and 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 cause problems too although the effect is a little more unpredictable as it can lead to either hypothyroidism or hyperthyroidism.

Toxic goiter (hyperthyroidism) under light microscopy
White haired older women rubbing her neck

Chapter 3

What are the symptoms of thyroid disease?

Symptoms of thyroid disorders can be debilitating but are often difficult to diagnose. We discuss the symptoms that you may recognise if you have thyroid disease. 

Although very common, thyroid disorders can be difficult to diagnose because symptoms are often overlooked (especially if mild) or are confused with those of other conditions. Below are some of the common symptoms experienced by people who have thyroid disease.

An underactive thyroid (hypothyroidism) is associated with a slowing down the body's metabolism. Symptoms of this condition include:

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

Thyroid in numbers

1 in 20

The number of people thought to be affected by a thyroid disorder


Women are up to 10x more likely to be affected by a thyroid disorder than men


Number of thyroid function tests performed by Medichecks


Age most likely to be diagnosed with a thyroid disorder

With an overactive thyroid (hyperthyroidism) the body’s metabolism speeds up. Symptoms of hyperthyroidism include:

  • 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
Tube of blood labelled Thyroid Test

Chapter 4

Diagnosing and managing a thyroid condition

Diagnosing your thyroid disorder usually starts with a blood test.  Here we look at what is commonly tested and what you can do to manage your condition.

If you have any of the symptoms above, determining whether you have a thyroid condition usually starts with a blood test. Here we look at what is commonly tested and what you can do to manage a condition.

An initial blood test

The simplest thyroid function tests examine your levels of thyroid hormones together with thyroid stimulating hormone (TSH) to check whether your thyroid is performing normally. A test to measure levels of TSH, FT4 and FT3 will give a complete picture of your thyroid hormone status although it is common for GPs in the UK only to test for TSH levels when investigating thyroid symptoms.

Thyroid Stimulating Hormone (TSH) is produced in the pituitary gland and stimulates the thyroid to produce thyroid hormones T4 and T3. TSH is produced in response to circulating levels of T4 and T3 – when levels of T4 and T3 are low (often the result of an underactive thyroid) TSH production is increased to stimulate the thyroid to produce more hormones. Raised TSH is commonly seen in cases of underactive thyroid (hypothyroidism). Conversely, low levels of TSH are often seen in response to high levels of thyroid hormones (overactive thyroid) as the body tries to reduce production of T4 and T3.

Free thyroxine (FT4) is the amount of thyroid hormone T4 that is not bound to proteins in the blood and is therefore free and available to be used by the body’s cells, where it is converted into T3. Low levels of FT4 may indicate an underactive thyroid while high levels are associated with an overactive thyroid.

Free triiodothyronine (FT3) is the active thyroid hormone that regulates metabolism in the cells. FT3 is T3 that is not bound to proteins and is considered a better measure of the level of hormone that can be used by the cells. Low levels of FT3 are commonly seen in people with an underactive thyroid while high levels often result from an overactive thyroid.

A comprehensive thyroid panel

More comprehensive thyroid panels include tests for thyroid antibodies. These may help to explain whether an autoimmune disorder such as Hashimoto's disease or Graves' disease is the underlying cause of a thyroid condition. Autoimmune disorders (where the body’s immune system attacks its own tissues) are very common causes of thyroid disease, especially in women. Thyroid antibody tests include:

Thyroglobulin antibodies (TGAb). Thyroglobulin is a protein used by the thyroid gland to produce T3 and T4. Ordinarily it does not enter the bloodstream, but if your thyroid is inflamed or under attack from your immune system, then thyroglobulin can be secreted and antibodies detected. Raised levels of thyroglobulin antibodies can indicate autoimmune thyroid disease.

Thyroid peroxidase antibodies (TPOAb). The thyroid gland produces the enzyme thyroid peroxidase which is required for the production of thyroid hormones. A TPOAb blood test looks for antibodies in the blood that target the thyroid peroxidase enzyme. High levels of antibodies indicate that the body's immune system is attacking the thyroid gland and impairing its function. Raised levels of TPOAb are often found in Hashimoto's disease and in many cases of Graves' disease.

An advanced thyroid profile

The most advanced profiles will also contain tests for thyroid nutrition – such as ferritin (iron stores), folate, vitamin B12 and vitamin D. Having optimal levels of these vitamins and minerals can help support your thyroid function. Deficiencies in these vitamins and minerals can also cause symptoms which can be confused with those of a thyroid disorder. Testing these markers helps to determine whether your symptoms are caused by a thyroid problem or a nutritional deficiency.

Bottle of Levothyroxine tablets

Everything you need to know

Everything you need to know

“A thyroid function blood test is simply the only way to accurately diagnose a thyroid disorder as so many symptoms are shared with other conditions”.

Dr Sam Rodgers

Medical Director

Managing your condition

Identify underlying health issues

If you are unsure whether your symptoms are thyroid-related, it is worth trying to find out first of all if there are other underlying health issues which might be causing your symptoms. If you haven't already had one we suggest a comprehensive blood test which tests your blood cells, kidneys, liver function, diabetes, iron status and vitamin B12/folate for anaemia, C-reactive protein (CRP) for inflammation and vitamin D.

Optimise vitamins and minerals

For those with diagnosed thyroid problems there is evidence that they may have lower levels of certain nutrients. Lower levels of selenium are associated with increased rates of hypothyroidism and with the development of some thyroid diseases. Approximately 40% of the UK population have less than the recommended daily intake of selenium in their diets. It is less clear whether selenium supplementation improves thyroid function in people with diagnosed thyroid disease. Iron deficiency is thought to decrease the body’s response to TSH and to cause lower levels of T3 and T4. Zinc supplementation has been shown to improve thyroid hormone levels in overweight or obese people.

Vitamin B12 deficiency and pernicious anaemia are common in people with hypothyroidism. Pernicious anaemia is easy to overlook so we recommend testing for it if you are found to have low vitamin B12 levels.

Iodine has a goldilocks relationship with thyroid function – levels that are too low or too high can both interfere with thyroid function. Iodine deficiency is rare in the UK, and some over-the-counter iodine supplements contain high levels which may push your blood levels above the top end of the normal range. Excess supplementation can cause an increase in thyroid antibodies in some people.

If you are planning to take vitamin or mineral supplements, then make sure you keep within the recommended ranges – sometimes too much supplementation can be as harmful as not enough.

Manage stress

High levels of thyroid stimulating hormone are associated with high levels of cortisol, the hormone your body produces when under stress. You can check your cortisol levels with a cortisol saliva test. This can detect slight increases in cortisol which are due to high levels of stress, as well as more serious abnormalities of cortisol. Adopting relaxation techniques such as meditation, getting regular and high-quality sleep as well as adopting a healthy diet and exercise plan can do much to relieve stress and correct mild abnormalities in cortisol levels.

Thyroid medication

Hypothyroidism is almost always treated using synthetic thyroid hormones which replace and play the role of the hormones that the thyroid gland is struggling to produce. Levothyroxine (synthetic T4) is commonly prescribed by GPs in the UK to people with an underactive thyroid to boost their levels of thyroxine. How you respond to medication will vary and will depend on dosage – it can often take months to find the right dose of levothyroxine to alleviate your symptoms. It is common to monitor hormone changes while starting medication with a thyroid function test – to better understand and control the effects that varying doses with have on your hormones.

Generally levothyroxine will help to improve the symptoms of an underactive thyroid. For some though it doesn’t work and this usually occurs where there is a problem in converting inactive T4 to active T3 in the body. Some practitioners will prescribe liothyronine (synthetic T3) either on its own or alongside levothyroxine to boost levels of T3 directly. Studies show that for the majority of people there is no benefit in taking T3 instead of levothyroxine. However, some people who are struggling to control their thyroid symptoms with levothyroxine alone may experience an improvement when taking T3.

We recommend that any medical treatment of a thyroid condition is started under the guidance of a specialist and is carefully monitored and managed to make sure that you don't take more thyroid hormone than you need.

Drugs, generally belonging to the class thioamides, are used to treat overactive thyroids and work by reducing the levels of thyroid hormones produced by the thyroid gland.

Middle aged women sitting in park thinking

Chapter 5

How often should I take a thyroid function test?

How often you test will depend on your diagnosis and symptoms. Below, we consider which frequency of testing may apply to you.

The frequency of thyroid testing is dependent on whether you have been diagnosed with a thyroid disorder and, importantly, whether you are experiencing symptoms.

If you are monitoring your thyroid function it is important that you always take the test at the same time of day so that you can compare results properly. We recommend taking your thyroid function test in the morning before you have taken any thyroid medication.

Results normal – no symptoms

If you have normal thyroid function test results and you have no symptoms then there is no need to repeat the test. We advise repeating the test in the future if you develop symptoms which you think might be thyroid-related.

Borderline results – no symptoms

A borderline TSH is between 4 mlU/L and 10 mlU/L. At this level, your TSH is above the normal range but below the level at which a doctor would typically treat. If your thyroid hormones are within the normal range and you aren’t experiencing any symptoms then we would recommend testing your thyroid function annually. Having an elevated TSH does raise the risk that you will develop an underactive thyroid in the future so we advise repeating the test if you develop any symptoms.

Borderline results – with symptoms

If your thyroid stimulating hormone (TSH) is borderline (between 4 mlU/L and 10 mlU/L), your thyroid hormones are normal but you are experiencing symptoms then we suggest repeating your test in 3 months. If you haven’t yet tested your thyroid antibodies then we would suggest doing so with your next test. Elevated antibodies also raise the risk that you will develop an underactive thyroid in the future. We would also recommend discussing your results and your symptoms with your doctor.

Known hypothyroidism – symptoms managed

If you have already been diagnosed with a thyroid disorder and are taking medication which is controlling your symptoms then you only need to check your thyroid hormones annually, or as often as your doctor recommends.

Known hypothyroidism – with symptoms

If you have been diagnosed with an underactive thyroid and are taking replacement hormone but are still experiencing symptoms then we suggest repeating a thyroid function test. We also recommend seeing your GP if this applies to you so that other causes for your symptoms can be ruled out.

Known hypothyroidism – changed medication dose

Once you have been diagnosed with an underactive thyroid it may take a period of time to get your dose of thyroid replacement right. Even if you have been taking medication for some time, it is not unusual for symptoms to reappear which may mean your dose will need adjusting. If you are taking too much thyroid replacement hormone then this could cause your metabolism to speed up causing symptoms like nervous anxiety, weight loss and sensitivity to heat. If you are not taking enough thyroid medication, or your thyroid condition gets worse, it can cause symptoms of an underactive thyroid such as weight gain, sensitivity to cold and low energy. We recommend repeating your thyroid function test 8 to 12 weeks after adjusting your dose.

Asian women and dog sleeping in bed

Chapter 6

How is an underactive thyroid diagnosed and treated?

Feeling constantly fatigued or cold, putting on weight, and having dry skin or hair can all be symptoms of an underactive thyroid. Here we look in detail at the causes, symptoms, diagnosis and treatment of an underactive thyroid.

An underactive thyroid (hypothyroidism) is one that is struggling to produce enough thyroid hormones to keep your metabolism on track. Here we take a detailed look at the causes and effects of an underactive thyroid.

When your thyroid gland fails to produce enough thyroid hormones to keep your metabolism running at a healthy rate, your body starts to slow down – your heart will beat more slowly, you take longer to digest and process your food and you won’t generate enough energy to keep your body feeling warm.

What causes an underactive thyroid?

Primary hypothyroidism

In primary hypothyroidism the problem lies with the thyroid gland itself – usually because it has been damaged in some way and cannot produce enough thyroid hormones. The most common reason for a damaged thyroid is an autoimmune disease called Hashimoto's thyroiditis. An autoimmune disease causes your body's immune system to attack and destroy your own cells and tissues, in this case the thyroid. Your thyroid gland can also be damaged by thyroid cancer as well as treatment for an overactive thyroid, where the gland is deliberately removed or destroyed.

Secondary hypothyroidism

In secondary hypothyroidism your thyroid functions normally, but there is a problem with the pituitary gland in your brain which regulates your thyroid. In this case, the pituitary gland fails to produce enough thyroid stimulating hormone (TSH) to cause the thyroid to produce more thyroid hormones.

Is an underactive thyroid hereditary?

There is a strong family link in the development of thyroid disorders – if a close family member already has thyroid disease (or any autoimmune condition), then your risk of developing an underactive thyroid is raised. This is because autoimmune diseases often run in families – your risk of developing any autoimmune disease is higher if a family member is also affected, and your risk of developing a thyroid disorder is raised if you already have another autoimmune condition such as lupus, rheumatoid arthritis or pernicious anaemia.

What are the symptoms of an underactive thyroid?

As thyroid hormones are needed for all bodily processes, when thyroid hormones are too low the symptoms can affect many parts of your body. The symptoms which are typically associated with an underactive thyroid include putting on weight, often feeling cold and lacking energy, having brain fog and constipation. Dry skin and hair, hair loss and muscle aches and pains are also commonly experienced by people who have an underactive thyroid.

How is an underactive thyroid diagnosed?

An underactive thyroid is diagnosed with a blood test. Your doctor will normally test for thyroid stimulating hormone (TSH), and sometimes (but not always) free thyroxine (FT4) which is the most plentiful thyroid hormone produced by the thyroid gland. If your TSH is above the normal range (over 4.2 mIU/L) and your FT4 is low it indicates that your thyroid is beginning to struggle to produce thyroid hormones. Most doctors will begin treatment once TSH is over 10 mIU/L. Some doctors however will consider treating a TSH below 10 mIU/L if it is accompanied by symptoms.

Why doesn't my doctor test for T3 (triiodothyronine)?

Although thyroxine (T4) is the most plentiful of the thyroid hormones, it is not biologically active and therefore has no impact on your cells' metabolism. To be active, it first must be converted to triiodothyronine (T3). This process takes place in the liver as well as other organs and the majority of people convert T4 to T3 without difficulty. This makes testing for FT3 unnecessary for most people. However, a small number of people do not convert T4 to T3 easily and, for them, testing for FT3 is a useful investigation. This is especially the case if they are still experiencing symptoms of an underactive thyroid despite normal levels of TSH and FT4.

Why doesn't my doctor test for thyroid antibodies?

Most cases of an underactive thyroid are caused by Hashimoto's thyroiditis, an autoimmune condition. In the case of an underactive thyroid, the thyroid gland is gradually destroyed which diminishes its ability to produce thyroid hormones. In most cases of hypothyroidism, an autoimmune condition is assumed, and does not require a confirmatory test.

Thyroid antibodies are not necessarily specific to thyroid disease – a positive antibody result together with normal levels of thyroid hormones usually does not mean that you have a thyroid disorder. For every 100 healthy people without thyroid disease, between 10 and 20 will have a positive thyroid peroxidase antibody result and will not go on to develop a thyroid condition. It is not necessary to test for thyroid antibodies routinely unless your endocrinologist has advised you to do so. If your levels of thyroid hormones are normal you do not need to discuss a positive thyroid antibody result with your doctor, unless you have been advised to do so by our doctors.

Why does Medichecks test for thyroid antibodies?

Many of our customers like to know if their antibodies are elevated. For someone without a diagnosis of thyroid disease (who may or may not be experiencing symptoms) it can help them to understand whether there is a risk that they might develop an underactive thyroid in the future (given that elevated antibodies raise your future risk of thyroid disease).

Those who have been diagnosed with thyroid disease and are undergoing treatment often monitor their thyroid antibodies along with their thyroid hormones. Autoimmune diseases often don’t develop in a straight line; sometimes they flare up which can cause a worsening of symptoms, while at other times they are stable or in remission. People whose thyroid symptoms are worsening often like to keep track of their thyroid antibodies.

How is an underactive thyroid treated?

An underactive thyroid is treated by replacing the thyroid hormone that you are no longer producing. For the vast majority, treatment is with levothyroxine, a synthetic form of thyroxine (T4). It can take several months to find the right dose of thyroxine to restore your thyroid hormones to a level where you feel normal again.

For some people, especially those who don’t convert T4 to T3 easily, treatment with thyroxine alone does not alleviate their symptoms. Some people respond better by incorporating some T3 into their treatment by taking liothyronine (a synthetic form of T3) alongside their levothyroxine. Please be aware that your doctor may not be able to prescribe T3 and you may need to be referred to an endocrinologist – even then the cost of T3 treatment may be prohibitive.

What are the health risks of having an underactive thyroid?

Untreated or under-treated hypothyroidism carries serious health risks which include:

  • Obesity
  • Joint pain
  • Raised cholesterol
  • Increased risk of heart disease
  • Infertility
  • Increased risk of miscarriage
  • Increased risk of birth defects
  • Depression
  • Peripheral neuropathy (damage to your peripheral nerves)
  • Puffy face

Will an underactive thyroid get better by itself?

Once your thyroid tissue is damaged it will not be able to repair itself. As Hashimoto's is not necessarily progressive, you may find that you do not need to increase your dose of thyroid replacement. However, most people with an underactive thyroid require thyroid replacement for the rest of their lives.

Is there a diet for an underactive thyroid?

Many people look to diet and lifestyle to see if they can support their thyroid function. In the case of the thyroid there are foods that are called goitrogenic which means that they can inhibit the ability of your thyroid to produce thyroid hormones. Goitrogenic foods include vegetables from the cruciferous family like broccoli, spinach, bok choy, swedes and turnips, as well as soy products and some fruits and plants including peanuts, strawberries and peaches.

Many of these foods are extremely nutritious so it is best not to avoid them all. Their effect on your thyroid function can be reduced by cooking them beforehand.

There are also a wide variety of vitamins and minerals that can support thyroid function including iodine*, selenium, iron, vitamin B12, folate and vitamin D.

*Only consider taking iodine if you have a properly functioning thyroid; if you are already taking thyroxine you do not need iodine. Do not take if you have an overactive thyroid as it can worsen your condition. Too much iodine can be as harmful to the thyroid as too little.

How is an overactive thyroid tested and treated?

Chapter 7

How is an overactive thyroid tested and treated?

Being hyper, anxious, fatigued, losing weight, and struggling to sleep are all symptoms of an overactive thyroid. Below we take an in-depth look at the causes, symptoms, diagnosis and treatment of an overactive thyroid.

Hyperthyroidism, or an overactive thyroid, occurs when the thyroid gland over-produces the hormones thyroxine (T4) and triiodothyronine (T3), speeding up the body’s metabolism. Here we taken an in-depth look at the overactive thyroid.

What can cause an overactive thyroid (hyperthyroidism)?

There are a number of causes of hyperthyroidism, with Graves' disease (an autoimmune condition) being the most common. In Graves' disease, the body's immune system produces antibodies that target the thyroid and increase the production of both T3 and T4. These antibodies are called thyroid-stimulating immunoglobulins (TSIs). TSIs mimic the role of thyroid stimulating hormone (TSH) which triggers the thyroid to produce hormones. Graves' disease often runs in families – having a close family member with the condition increases an individual's risk of developing an overactive thyroid. Like many autoimmune diseases, women are at a greater risk of developing Graves' disease than men. Other causes of hyperthyroidism include:

  • Thyroiditis which is the inflammation of the thyroid gland. Caused by either a problem with the immune system or a viral infection, inflammation causes thyroid hormones that are stored in the gland to leak into the bloodstream.
  • Certain medications including amiodarone, lithium, interferon alpha and interleukin-2 can affect the production of thyroid hormones.
  • A toxic nodular goitre (TNG) is an enlarged thyroid with independently functioning thyroid nodules, capable of increasing the levels of thyroid hormones produced. TNG is often caused by low iodine levels in the body.
  • Low iodine levels encourage the thyroid to grow in size, absorb as much iodine as possible and create excess levels of thyroid hormones. Excessively high levels of iodine can also result in hyperthyroidism.

What are the symptoms of hyperthyroidism?

Hyperthyroidism causes an increase in metabolic rate which causes symptoms such as fatigue, unexplained weight loss, feeling anxious, a rapid heartbeat and/or heart palpitations and difficulty sleeping. Other classic symptoms of Graves' disease are an enlarged thyroid gland (goitre) and a protuberance of one or both eyes (exophthalmos).

How is hyperthyroidism diagnosed and treated?

Symptoms of an overactive thyroid, especially in the early stages, might be missed or mistaken for other conditions. It’s not uncommon for some people to put their weight loss, rapid heartbeat and sensitivity to heat down to stress or anxiety. A blood test to measure thyroid hormone and antibody levels is used to diagnose hyperthyroidism. There are many ways to treat an overactive thyroid:

  • Medications such as thioamides, which are a group of drugs used to treat hyperthyroidism, work by reducing the levels of thyroid hormones produced. Methimazole and propylthiouracil which belong to this drug class, are the most commonly used.
  • Radioiodine treatment can be used to treat hyperthyroidism. Radioactive iodine is taken in by the thyroid and destroys the thyroid cells, which ultimately reduces the levels of hormones produced and decreases the size of the enlarged gland.
  • Surgery can also be used to treat hyperthyroidism and involves either removing a small section of the thyroid or the whole gland. After surgery, an individual may be required to take synthetic thyroid hormones to ensure they do not develop hypothyroidism. If the entire thyroid is removed, then lifelong thyroid hormone replacement therapy is needed to maintain hormone levels in the body.

How are thyroid blood tests affected by hyperthyroidism?

In the most common forms of hyperthyroidism, it is the thyroid gland which is responsible for producing too much T3 and T4. In these conditions, the pituitary gland is functioning normally so TSH production will be reduced. Low TSH levels will be accompanied by high FT4 and high or high normal FT3 results.

There are rare forms of hyperthyroidism in which the pituitary gland malfunctions and produces too much TSH. Although the thyroid gland is healthy, it is overstimulated by TSH and produces too much T3 and T4. In this case TSH, FT4 and FT3 results are all elevated.

If you think that you may have hyperthyroidism, it is important to see your doctor promptly as the condition can deteriorate rapidly.

Thyroid Health FAQs

Thyroid Health FAQs
Are Medichecks tests accurate?

We only use laboratories which have been accredited by UKAS, the UK's accreditation service. This means that they are subject to the same stringent review procedures as an NHS laboratory.

How will I know what my results mean for me?

Your results will come with a comment from a qualified doctor. We’ll let you know what your results mean and what action you need to take next.

Will my doctor recognise my results?

Your doctor should be able to use your Medichecks results to make a diagnosis and provide treatment. Find out more about why you can trust our results.

Do you share my results with my doctor?

No, we don’t share your results with anyone. We make it easy to share your results with your doctor if you choose to – simply download the PDF report in your dashboard.

Should I tell you what thyroid medication I’m taking?

Yes, absolutely. Your results will be affected by what thyroid medication you are taking, especially if you are taking any form of T3 (liothyronine).

Two women in a library researching

Chapter 8

Glossary of thyroid terms

Medical terminology can be confusing.  This glossary explains in simple language the key terms used to describe the thyroid, its diagnosis and management.

Autoimmune disease

Autoimmune disease occurs when the body's immune system begins attacking its own cells. Autoimmune diseases include rheumatoid arthritis, lupus, psoriasis, pernicious anaemia, multiple sclerosis as well as thyroid disorders Hashimoto's thyroiditis and Graves' disease.


Euthyroid means that levels of thyroid hormones are within the normal range.

Free T3

T3 (triiodothyronine) is the biologically active thyroid hormone produced by the thyroid gland. Some T3 is bound to proteins in our blood and is therefore unavailable to our cells. Free T3 is the unbound or available hormone and is generally a better measure of thyroid status than a T3 blood test.

Free T4

T4 or thyroxine is the main hormone produced by the thyroid gland. Some T4 will attach to proteins in the blood which means that it is not available to be converted to T3, the biologically active thyroid hormone. A blood test to measure Free T4 can be a more active measure of available T4.


A goitre is caused by the enlargement of the thyroid gland, which produces a swelling in the neck. It occurs when the thyroid is struggling to produce enough thyroid hormone for the body's needs, either because of insufficient dietary iodine or because the thyroid gland is under attack from the body's immune system. In these circumstances, the pituitary gland stimulates the thyroid to produce more thyroxine, causing it to enlarge. Graves' disease can also cause a goitre, although in this instance too much thyroid hormone is being produced.

Graves' disease

Graves' disease is an autoimmune disease that causes the thyroid to produce excess levels of thyroid hormones. It can cause goitre and bulging eyeballs which are commonly associated with an overactive thyroid. It is named after Robert Graves who described it in 1835.

Hashimoto's thyroiditis

Hashimoto's thyroiditis or Hashimoto's disease is an autoimmune disease where the body's immune system attacks cells of the thyroid gland, resulting in lower production of thyroid hormones. Hashimoto's disease is named after Hakaru Hashimoto who first described it in 1912.


Hyperthyroidism is the name given to an overactive thyroid gland, causing nervousness, weight loss, fatigue, diarrhoea and a host of other symptoms.


Hypothyroidism is the term given to an underactive thyroid gland, causing tiredness, cramps, a slowed heart rate, weight gain amongst many other symptoms.


Levothyroxine is the synthetic thyroxine (which is chemically identical to T4) that is prescribed within the NHS to treat hypothyroidism.


Liothyronine is a synthetic form of the active thyroid hormone T3. It is used in some patients to treat suspected hypothyroidism when problems occur in converting T4 to T3 for use by the body's cells. This may be due to a deficiency in deiodinase enzymes.

Natural desiccated thyroid (NDT)

Natural desiccated thyroid is sometimes known as ‘armour thyroid’ or NDT. In the UK the NHS uses the synthetic thyroid replacement hormone, levothyroxine (or T4) to treat hypothyroidism. However, some practitioners believe that certain patients do not respond symptomatically to this approach and so use NDT instead. NDT is actual thyroid tissue (usually acquired from pigs), which has been dried to a powder and contains natural T4 and T3.

Overactive thyroid

Overactive thyroid is the familiar term for hyperthyroidism which means that the thyroid gland produces excess levels of thyroid hormones resulting in a raised metabolism.

Pernicious anaemia

Pernicious anaemia is an autoimmune disease in which the body's immune system attacks cells in the stomach leaving it unable to absorb vitamin B12. Vitamin B12 is essential for the production of normal red blood cells. Symptoms include excessive tiredness, numbness in the arms and legs, weakness and unsteadiness.

Pituitary gland

The pituitary gland is a small, round gland located at the base of the brain that releases hormones that control other glands (such as the thyroid) in the body.

Reverse T3 (rT3)

Triiodothyronine (T3) is the active thyroid hormone which governs metabolism in our cells. It is produced from T4 by the removal of an atom of iodine. At times, the wrong atom is removed resulting in reverse T3. Reverse T3 can block the action of T3 in our cells. Small amounts of rT3 are normal and actually regulate T3 uptake in our cells, but in times of stress more rT3 is produced which limits the action of T3. This can cause symptoms associated with an underactive thyroid even though blood test levels of T4 and T3 may be normal.

Sick euthyroid syndrome

Sick euthyroid syndrome (or euthyroid sick syndrome) is a condition where the measured levels of thyroid hormone (usually T3) are low, but without any accompanying symptoms of hypothyroidism. This usually occurs when the patient is very unwell for other reasons and is seen commonly in patients being treated in intensive care units with multiple medical problems.


Thyroglobulin is a protein contained in abundance within the thyroid gland from which the hormone thyroxine is manufactured. It contains tyrosine molecules, which when bound to 4 iodine atoms form thyroxine (T4).

Thyroid antibodies

Thyroid antibodies are immunological weapons that target different proteins in the thyroid gland as part of an autoimmune disorder such as Hashimoto’s or Graves' disease, where the immune system turns itself onto the body’s own tissues.

Thyroid gland

The thyroid gland is located in the front of the neck below the voice box and plays an important role in metabolism where oxygen and calories are converted to energy. The thyroid gland is responsible for producing thyroid hormones thyroxine (T4) and triiodothyronine (T3).

Thyroid nodule

Thyroid nodules are very common, especially in people over the age of 60. They are caused when there is abnormal growth of thyroid cells which cause lumps on the thyroid gland. The vast majority of thyroid nodules are benign but a small proportion are cancerous. Normally a thyroid nodule will be investigated through a biopsy. Sometimes thyroid nodules can affect swallowing and breathing, but normally they do not produce any symptoms.

Thyroid peroxidase

Thyroid peroxidase is an enzyme found within the thyroid gland which is essential for thyroxine hormone production. It converts iodide (which arrives at the thyroid gland in the bloodstream) to iodine which in turn gets bound to tyrosine to form thyroxine.

Thyroid stimulating hormone (TSH)

Thyroid stimulating hormone (TSH) is produced in the pituitary gland at the base of the brain to stimulate thyroid hormone production. If blood levels of thyroid hormones are high, the pituitary signals the thyroid to stop production, whereas if thyroid hormone levels are low it will signal to increase production. TSH is often measured as a proxy for thyroid hormones.

Thyroid storm

A thyroid storm is caused by extreme hyperthyroidism. Symptoms include rapid heartbeat, raised blood pressure, exhaustion and fever. It is caused by under-treated or untreated hyperthyroidism and can often be fatal.


"Itis" simply means inflammation. Thyroiditis is inflammation of the thyroid gland.

Thyroxine (T4)

Thyroxine is also known as T4 and is the predominant hormone produced by the thyroid gland. It is known as T4 because it uses 4 atoms of iodine (taken from the food we eat). Thyroxine isn't active in our cells and must convert to triiodothyronine (T3), the active thyroid hormone, before it can influence our body's metabolism.

Triiodothyronine (T3)

Triiodothyronine (T3) is a potent thyroid hormone which governs metabolism in our body's cells. The thyroid gland produces some triiodothyronine, but most of is derived from thyroxine (T4) which loses an atom of iodine to become T3.

Underactive thyroid

Underactive thyroid is the familiar term for hypothyroidism. It means that the thyroid gland produces insufficient levels of thyroid hormone to maintain the body's metabolism at its normal rate.