The thyroid is a small gland in the front of the neck just below the voice box (larynx), and is made up of two parts, or lobes. It is one of a network of glands throughout the body that make up the endocrine system. This system is responsible for producing the body's hormones that help to control and influence various functions. The thyroid is sometimes known as the 'activity' gland because it produces the two main hormones, thyroxine (T4) and triiodothyronine (T3), which are needed to keep the body functioning at its normal rate. In order to produce the thyroid hormones, the thyroid gland needs a regular supply of iodine (which is found in fish, seafood and dairy products).
If the levels of T3 and T4 in the blood fall, the hypothalamus (a part of the brain) sends out thyroid-releasing hormone (TRH) into the blood. As the levels of TRH in the blood rise, the pituitary gland releases thyroid-stimulating hormone (TSH) which stimulates the thyroid to produce more thyroid hormones.
If the thyroid gland doesn't produce enough hormones you will feel tired and lethargic and put on weight easily. This is called hypothyroidism, or myxoedema.
If the thyroid gland produces too much hormone you will lose weight, have an increased appetite, feel shaky and anxious, or have palpitations. This is known as hyperthyroidism, or thyrotoxicosis.
Dr Gill Jenkins and Dr Rob Hicks, BBC as at Dec 2005
The thyroid gland in the neck controls metabolism through the production of thyroid hormone. It may become overactive, called hyperthyroidism, or underactive, called hypothyroidism.
The thyroid gland sets the rate at which you produce energy from your body stores by the release of thyroid hormones.
If you're producing too much hormone, and the gland is overactive, you're said to be hyperthyroid. You'll have too much energy, lose weight, feel warm and may have symptoms such as palpitations.
There are many causes of an overactive thyroid and you may need blood tests and scans to find out what's responsible. The most common reason is where your body's defences falsely recognise your own tissue as an invader and begin to attack it. This is called auto-immune disease and it stimulates the thyroid to produce more hormones. If you have a cyst or growth in the thyroid, it may also produce too much hormone.
Hyperthyroidism symptoms may include:
If it's under-active, not producing enough hormone, you'll have too little energy and will feel slow, tired and lethargic. You'll become hypothyroid. Again, there are many causes, but for some it seems to be part of the ageing process. Hypothyroidism is especially common in women after the menopause. Look out for the following symptoms:
Up to one in 50 people are affected. It can occur at any age but is most common between the ages of 20 and 50.
Hypothyroidism is ten times more common in women than in men and usually occurs over the age of 40.
It's difficult to prevent thyroid illness.
Hypothyroidism is treated with thyroid hormone medication.
Treatment of hyperthyroidism may involve medication to reduce the production of thyroid hormone, radioactive iodine therapy, or thyroidectomy (removal of part of the thyroid gland).
BUPA , February 2004
Hyperthyroidism means having an overactive thyroid gland. It results in an excess of the thyroid hormones, making the body's functions "speed up" and causing symptoms such as restlessness, anxiety and weight loss.
Approximately 1 in 50 women and 1 in 1000 men develop hyperthyroidism each year in the UK. Once diagnosed, hyperthyroidism can usually be treated successfully.
The thyroid gland
The thyroid gland is found in the neck. It lies in front of the wind-pipe (trachea), above the level of the collarbones and measures approximately 2 by 4 cm. It secretes hormones, which are chemicals produced by the body to help regulate how cells, and the organs made up of those cells, work. Hormones are sometimes called chemical messengers.
The thyroid hormones are thyroxine (also called T4 because it contains four iodine atoms) and triiodothyronine (also called T3 because it contains three iodine atoms). These are released into the blood stream.
T3 speeds up the body's metabolism by encouraging the cells, in the muscles or the skin for instance, to work faster or to grow. Most of the T3 in the blood is converted from T4.
Over and under-active thyroid
With hyperthyroidism, over-production of T3 and T4 can cause the body's metabolism to speed up resulting in characteristic symptoms. In contrast, hypothyroidism results when the thyroid is underactive and produces too little thyroid hormone. This slows down the body's metabolism. For more information on hypothyroidism please see the separate BUPA factsheet Underactive thyroid (hypothyroidism).
The production of T3 and T4 is regulated by another hormone called TSH (thyroid stimulating hormone or thyrotropin) which is made in the pituitary gland (found in the brain). A normal level of TSH is one of the indicators that the thyroid system is working properly.
Causes of hyperthyroidism
This is the most common cause of hyperthyroidism in the UK, accounting for 60 to 80% of cases. Graves' disease is an "autoimmune" disease. Antibodies are proteins designed to defend the body from foreign organisms, such as bacteria and viruses. In autoimmune conditions, antibodies attack the body itself. In Graves' disease, antibodies cause the thyroid gland to produce too much thyroid hormone.
Nodular thyroid disease
Nodules - small lumps - within the thyroid account for the majority of the other cases of hyperthyroidism. Abnormal thyroid tissue within these nodules produces too much thyroid hormone. If one nodule forms, this is called toxic solitary adenoma. If more than one forms, this is called toxic multinodular goitre.
There are other rare causes of hyperthyroidism. In thyroiditis, there is inflammation of the thyroid gland from either infection or autoimmune attack. Thyroiditis can also be associated with pregnancy. Too much iodine in the diet (or taking drugs containing iodine) is a further cause of hyperthyroidism.
Hyperthyroidism can cause many different symptoms and the overall pattern can vary for different people, depending on their age and the amount of excess hormone being released. In general, the symptoms relate to a "speeding up" of the body's metabolism and they include the following:
Diagnosis of hyperthyroidism
Many of the above symptoms are quite general and could be caused by conditions other than an overactive thyroid. However, anyone who notices these symptoms should consult their GP. A doctor will usually discuss symptoms, carry out a physical examination, and then request some blood tests if he or she suspects hyperthyroidism.
Hyperthyroidism can be confirmed relatively easily by doing some blood tests, although the underlying cause may need a little more investigation. A blood test to determine the amount of thyroid stimulating hormone (TSH) is usually done first. If this is normal, T3 and T4 are also likely to be normal. However, if the TSH is abnormal, T4 and T3 levels may also need to be checked. In some circumstances the presence of certain antibodies may be confirmed with another blood test.
The thyroid gland itself may be checked using a test called scintigraphy. This involves injecting a radioactive form of iodine. The thyroid uses this iodine to make T3 and T4, which means certain parts of the gland take up the radioactive material and can be seen with a scanner. The dose of radioactivity is very low and is not dangerous.
Ultrasound scanning can help measure the size of a goitre and whether it is pressing on neighbouring tissues in the neck. CT or MRI scanning may also be needed to assess eye problems.
Treatment of hyperthyroidism
In a minority of cases, hyperthyroidism clears up on its own. But in most cases, it needs treating and tends to recur if treatment is stopped.
Treatment aims to bring thyroid hormones down to normal levels - this state is known as being "euthyroid".
Treatments for hyperthyroid include:
These drugs suppress the production of thyroid hormones. Examples include carbimazole and propylthiouracil. Too much of these drugs can cause hypothyroidism and regular blood tests are needed to check the correct amount has been taken. Another way of giving these drugs is called the block - replace regimen, where output of the thyroid is completely suppressed and replacement thyroxine (T4) is given in tablet form (thyroxine replacement therapy).
An episode of Graves' disease can get better after 1-2 years of treatment, although relapses are common once treatment is stopped.
This is iodine that has been made radioactive, similar to the iodine used for a scintigraphy scan. The body uses iodine to make T3 and T4, so when the radioiodine is given as a tablet, or drink, it is taken up into the thyroid gland. As the radioactivity builds up in the thyroid gland, it destroys some of the thyroid tissue. If just the right amount is given, it may be possible to return the thyroid hormones to the correct level, but this can be difficult.
Sometimes, a single large dose of radioiodine is given, with the intention of stopping all thyroid activity, followed by thyroxine replacement therapy. The dose of radioactivity to the rest of the body is low and is not dangerous. However, radioiodine is not used in pregnant or breastfeeding women.
This is used to remove a single nodule (toxic solitary adenoma). It may also be used when there is a large goitre or if drug treatment has failed.
As with any surgery, there are risks. These include bleeding, infection or damage to nearby nerves or other tissues. The surgeon will discuss these with each patient before surgery.
Drugs called beta-blockers (eg propranolol or atenolol) are sometimes used to treat the symptoms of hyperthyroidism, for example while waiting for a treatment such as radioiodine to become fully effective.
Treatment for eye problems
Some people need treatment for eye symptoms relating to Graves' disease. These include eye drops, sunglasses or eye protectors for sleeping. Treatment for more severe eye problems might include steroid tablets, radiation treatment or surgery.
BUPA, February 2004
Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormones. This tends to slow down the body's functions. Symptoms include tiredness, constipation and sensitivity to the cold.
Approximately 1 in 50 women and 1 in 1000 men will develop symptoms of hypothyroidism at some stage in their lives. Once diagnosed, treatment is usually straightforward.
Over- and underactive thyroid
In hypothyroidism, the thyroid is under active, with too little of the thyroid hormones being released. In contrast, hyperthyroidism occurs when there is over-production of T3 and T4, causing the body's metabolism to "speed up". This results in symptoms such as anxiety and feeling hot, even in cool weather. For more information, please see the separate BUPA factsheet Overactive thyroid (hyperthyroidism).
The production of T3 and T4 is regulated by another hormone called TSH (thyroid stimulating hormone or thyrotropin) which is made in the pituitary gland (found in the brain). A normal level of TSH is one of the indicators that the thyroid system is working properly.
Causes of hypothyroidism
The chemical element iodine is a major component of thyroid hormones. Worldwide, a deficiency of iodine in the diet is the leading cause of hypothyroidism. This is much less common in the UK because iodine is contained in salt, which has iodine added to it during manufacture.
In the UK, and other countries where the amount of iodine in the diet is adequate, the main cause of hypothyroidism is "autoimmune hypothyroidism".
Antibodies are proteins designed to defend the body from foreign organisms, such as bacteria and viruses. In autoimmune diseases, antibodies attack the body itself. In autoimmune hypothyroidism, antibodies destroy thyroid gland cells preventing the gland from being able to release normal amounts of thyroid hormones.
A condition known as Hashimoto's thyroiditis is associated with autoimmune hypothyroidism. It results in a goitre, a swelling of the thyroid gland, that is visible as a lump on the neck. With no goitre the condition may be called atrophic thyroiditis or primary myxoedema.
Treatment for hyperthyroidism
Hyperthyroidism is the result of an overactive thyroid gland. Treatments for hyperthyroidism, such as surgery or treatment with radioactive iodine or other antithyroid drugs can often result in hypothyroidism.
Congenital hypothyroidism (a condition babies are born with) happens when the thyroid gland fails to develop properly or does not produce adequate thyroid hormones. All babies in the UK are screened for this when the baby is 6-8 days old with a blood sample taken from a prick on the heel. With treatment, babies with congenital hypothyroidism develop normally.
Inflammation of the thyroid gland (thyroiditis) due to infection can lead to hypothyroidism. Also, disorders of the hypothalamus and pituitary gland, both of which are involved in the overall regulation and production of thyroid hormones, can lead to hypothyroidism.
Risk factors for hypothyroidism
The symptoms of hypothyroidism can initially be very mild and develop slowly. It is possible to have some of these symptoms before the amount of thyroid hormone drops below normal.
This type of mild hypothyroidism is called subclinical hypothyroidism. People affected need to be monitored by their doctor, who will watch out for further symptoms.
The symptoms of hypothyroidism relate to a general "slowing down" of the body's functions. They include:
Diagnosis of hypothyroidism
Many of the above symptoms can be caused by conditions other than underactive thyroid. However, anyone who experiences these symptoms should consult their GP. A doctor will usually discuss symptoms, perform a physical examination and then request some blood tests if he or she suspects hypothyroidism.
The first step in diagnosing hypothyroidism is to measure TSH (thyroid stimulating hormone).
When the thyroid gland is not producing enough thyroid hormone, the TSH level is raised. When this abnormality is found, T4 (thyroxine) is also measured, and in autoimmune hypothyroidism or hypothyroidism due to treatment of hyperthyroidism, T4 is low.
When levels of TSH and thyroid hormones are difficult to interpret, other causes of hypothyroidism may be suspected.
The diagnosis of autoimmune hypothyroidism is usually confirmed by the presence of particular antibodies in the blood.
Other blood tests or further investigations may also be needed. These could include an ECG (heart tracing) or a magnetic resonance imaging (MRI) scan to examine the nature and extent of a goitre.
Thyroxine (T4) can be given in tablet form. The body is able to convert this to T3 just as it would if the thyroid gland were producing the thyroxine normally. It can take some time to get the dose right. It is usual to start with a low dose, building up gradually every six weeks and adjusting the dose according to TSH levels.
People usually feel much better once they are taking thyroxine. Side-effects are unusual because a missing hormone is simply being replaced. However, if too much replacement thyroxine is given, symptoms of an overactive thyroid may be experienced.
People with subclinical hypothyroidism may not have any treatment, though doctors vary in their approach. Some prefer to offer treatment. Others recommend frequent monitoring to see whether overt hypothyroidism (with symptoms) does develop.
Once the correct dose of thyroxine replacement has been established, it is usual to have annual checks of TSH.
Pregnancy and hypothyroidism
The functioning of the thyroid gland can change during pregnancy. In the first half of pregnancy it is normal for the total amount of thyroid hormone to be slightly increased.
Women with hypothyroidism need more frequent checks during pregnancy, as their thyroxine requirements tend to increase.
Five percent of women have a mild problem with the thyroid three to six months after delivery. This has an autoimmune cause and can cause hyperthyroidism or hypothyroidism. Although it rarely needs treatment it does mean that thyroid problems are more likely in later life.
Each year, approximately 1,400 people in the UK are diagnosed with thyroid cancer. It is a rare cancer that usually affects middle-aged and older people. However, one type of thyroid cancer (papillary) can occur in younger people. Thyroid cancer is more common in women than men, and very rare in children.
There are four main types of cancer of the thyroid. By examining cells from the cancer, your doctor will be able to tell which type you have. This gives information about the best type of treatment for you.
Papillary This is the commonest type of thyroid cancer.
Follicular This is a less common type of cancer, usually found in older people.
These two types are sometimes called differentiated thyroid cancer and they are often treated in the same way.
Medullary This is a rare type of thyroid cancer that may run in families. For this reason, members of your family may be checked at regular intervals to ensure they are not showing any signs of the cancer.
Anaplastic This is also a rare type of thyroid cancer. It occurs more commonly in older people and grows quickly. Unlike other types of thyroid cancer, it can be difficult to treat.
It is also possible to have a lymphoma of the thyroid gland. This is another rare type of cancer, which starts in the lymph tissue of the thyroid. The lymph tissue is part of the body's immune system. Usually thyroid lymphomas are a type of non-Hodgkin lymphoma (NHL).
Apart from the anaplastic type and lymphoma, cancer of the thyroid tends to develop very slowly, and it may be some years before it starts to cause any problems. With treatment, the outlook for most people with cancer of the thyroid is very good and many people are completely cured, even if the cancer has spread beyond the thyroid.
Causes of thyroid cancer
The exact causes of thyroid cancer in most people are not known. In some people it can be linked to previous radiation exposure. This may be due to radiotherapy given in childhood, or to unusually high levels of radiation in the environment: for example, in the areas surrounding Chernobyl, in the Ukraine, following the nuclear power explosion of 1986. However, only a small number of cases of thyroid cancer are caused by radiation exposure.
People who eat very little iodine in their diet are more likely to develop thyroid cancer.
In a very small number of people, medullary thyroid cancer may be due to an inherited faulty gene. There are two main types of inherited condition in which this occurs:
How does an overactive thyroid affect the heart?
An untreated overactive thyroid increases the rate at which the heart beats causing it extra stress and work. You may notice a faster heart rate and could experience irregular heartbeats, which are referred to as atrial fibrillation. This may be present all the time and may be especially noticed in elderly patients.
What is cholesterol and how is it related to my thyroid gland?
Cholesterol is a particular type of fat in the blood and is partially influenced by the amount of thyroid hormones secreted by the thyroid gland. If a person has an underactive thyroid then the cholesterol may be higher than normal. Once the thyroid disorder is treated and maintained within the reference range the cholesterol levels should go back to their previous levels. An increase in blood pressure may also be found in people with an untreated underactive thyroid disorder.
Can hypothyroidism lead to angina?
Also starting with a large dose of thyroxine will increase metabolism and therefore increase heart rate. But if the arteries are narrowed or furred then this too can cause angina. In this case it is better to start with small doses of thyroxine over a 3-4week period and increase slowly.
Is my thyroxine treament causing my angina?
Angina may become worse while given thyroxine but it is not the thyroxine causing the Angina. It is the case that the hypothyroid state artificially helps angina by slowing down the metabolism and thus reducing the stress on the heart, and once thyroxine is taken the heart rate will increase to what it should be working at normally, therefore aggravating the angina you already have.
Is there a connection between thyroxine treatment and hypertension?
I don’t know of any connection between thyroxine treatment and hypertension. Both thyroxine treatment for an underactive thyroid, and hypertension, are common conditions and may very well co-exist in the same individual. Having an unmanaged underactive thyroid may contribute to a raised level of cholesterol and thus increasing blood pressure due to furring for the arteries. But this is usually corrected with adequate thyroxine therapy.
High blood pressure may be the feature of untreated or inadequately treated hypothyroidism but should also return to normal with appropriate dosage of thyroxine. Normally the recommendation would be a dose of thyroxine which restores the thyroid stimulating hormone (TSH) concentration to the lower part of the normal range i. e. below 2. 0 mU/l.
What are Beta-blockers and why are they needed?
Beta-blockers are often used for high blood pressure by slowing down the heart rate and therefore relieving palpitations, reducing perspiration, tremors, and anxiety. The most commonly used beta-blocker is Propranolol, which is generally a very safe drug but should not be taken if you suffer asthmatic tendencies. Beta-blockers do not have any curative value but will help you feel more comfortable until a proper cure is reached. When treatment no longer requires beta-blockers, the dosage will be gradually reduced over a week to 10 days before the drug is finally stopped.
Four tiny parathyroid glands are located around the thyroid in the throat. ‘Para’ means ‘near’, which explains the name. These glands are part of the endocrine system, which consists of a range of glands that secrete hormones into the bloodstream.
The main function of the parathyroid glands is to make the parathyroid hormone (PTH). This chemical regulates the amounts of calcium, phosphorus and magnesium in the bones and blood. The minerals calcium and phosphorus are crucial for healthy bones. Blood-borne calcium is also needed for the proper functioning of muscle and nerve cells. When calcium levels in the blood are too low, the parathyroid glands release extra PTH, which leeches calcium from the bones and stimulates calcium reabsorption in the kidney. On the other hand, if the level of calcium in the blood is too high, the glands drop hormone production.
Problems can occur if the parathyroids are overactive or underactive.
Around one in every 2,000 people has overactive parathyroids, or hyperparathyroidism. Women aged 50 years and over are more likely to develop the condition. The glands make too much hormone and allow the calcium levels in the blood to rise. Meanwhile, the bones are robbed of vital calcium and the kidneys are placed under great strain.
Up to 50 per cent of patients with hyperparathyroidism present with symptoms due to kidney stones. A small tumour (adenoma) is usually the cause of hyperparathyroidism. Other causes include chronic kidney (renal) disease or particular medications, such as anticonvulsant drugs.
Symptoms of hyperparathyroidism may include:
Hypoparathyroidism is characterised by low levels of PTH, which decreases the amount of calcium in the blood. Nerve and muscles cells are unable to function properly.
Causes of hypoparathyroidism include magnesium deficiency, injury to the glands, surgery on the nearby thyroid gland, genetic disorder or the congenital lack of parathyroid glands.
Symptoms of hypoparathyroidism include:
The parathyroid glands are part of the endocrine system. Other glands include the pituitary, pancreas, adrenals and thyroid. Multiple endocrine neoplasia 1 (MEN1) is an inherited condition, characterised by tumours on at least two of these glands. Symptoms depend on which glands are affected, but may include:
Complications caused by untreated parathyroid disorders can include:
Diagnosing parathyroid problems depends on the condition, but may include:
Treatment depends on the condition and its severity, but may include:
Parathyroidectomy is an operation to remove the parathyroid glands. Partial parathyroidectomy means at least one gland is left intact to help the body regulate calcium. The complete set of glands is removed during a total parathyroidectomy. Complications of surgery include injury to the nearby thyroid gland.
Where to get help
Ear, nose and throat specialist
Things to remember
Merril W. Edmonds MD, FRCP(C), Endocrinologist, London Health Sciences Centre
Mrs. Smith, a 36-year-old single mom with 3 children and a fulltime elementary school teacher, has had sole responsibility for her children (12, 10, and 7 years) since her husband died in a car accident 3 years ago.
Over the past couple of years she has been extremely tired and can barely muster enough energy to get through the day. Her mother had a thyroid problem and her sister who had recently been experiencing extreme fatigue, was diagnosed with hypothyroidism and now feels much better since starting thyroid hormone. Mrs Smith went to see her doctor hoping she was hypothyroid but her thyroid tests were normal. Her doctor told her that her fatigue was not due to her thyroid but Mrs. Smith is desperate for help and thinks the tests must be wrong.
Mr. Jones, a 43-year-old, has always had trouble keeping his weight down. He was always dieting and exercising until a couple of years ago when he suddenly started to lose weight despite eating a lot more than usual. He was subsequently diagnosed with hyperthyroidism and treated with a drink of radioactive iodine. Within three months he was again putting on weight, developed muscle cramps, and was becoming cold and puffy. Hypothyroidism was diagnosed and he was started on thyroxine but he continued to gain weight.
Repeat thyroid tests indicated his thyroid levels were back to normal but Mr. Jones found that he had to eat even less than before and exercise even longer in order to keep his weight down. He wonders if the tests are wrong and feels he should be taking more thyroid hormone.
Although Mrs. Smith and Mr. Jones are fictitious, they are typical of many patients that are referred to endocrinologists. Fatigue and weight gain are two of the most common symptoms that bring people to see their family doctor.
Can the thyroid cause these symptoms?
Can we be sure the tests are accurate? What would happen if I took a little more thyroid hormone than the doctor advised? Before we try to answer these questions it would be best to review the role of the thyroid and the tests we use to determine if the thyroid is functioning normally.
Thyroid hormone - Cruise Control for the Body
The thyroid gland's role in the body is very similar to cruise control in the car. Cruise control keeps a car running at a constant steady speed. When we do not want to worry about having to keep a steady foot on the accelerator we turn on cruise control and the car maintains a normal speed without any effort. Thyroid hormone keeps the rest of the body working at the right speed. If thyroid hormone levels decrease, cells throughout the rest of the body decrease in activity. As a result the cells need less energy and thus more energy is available to be stored and the weight increases even though the appetite decreases. Less heat is produced, the person becomes cold, and the sweat glands do not keep the skin moist anymore. The brain just wants to sleep all the time. The heart beats slower. The bowels become sluggish. Everything slows up.
The thyroid gland's role in the body is very similar to cruise control in the car. Cruise control keeps a car running at a constant steady speed
If thyroid levels increase, cells throughout the rest of the body increase in activity. As a result more energy is used up, fat and protein stores are mobilised and the weight decreases even though the appetite increases. More heat is produced as a by-product and the person becomes hot, and sweating increases in an effort to get rid of the heat. The brain works overtime resulting in irritability and shakiness, and sleep becomes difficult. The heart beats faster and harder. Bowel activity increases. Everything speeds up.
The Pituitary - Setting the Cruise Control
The master gland, the pituitary, which is situated at the base of the brain and between our temples, is responsible for setting the level of function for the thyroid gland and thus the level of thyroid hormone in the blood stream.
If thyroid hormone levels in the blood decrease even a little, the pituitary puts out more Thyroid Stimulating Hormone (TSH) which travels through the blood to the thyroid where it stimulates the thyroid gland to make and release more thyroid hormone. If thyroid hormone levels increase for some reason, the pituitary stops secreting TSH into the blood stream and the thyroid is no longer stimulated to make and secrete thyroid hormone into the circulation.
The main thyroid hormone produced by the thyroid gland is thyroxine (T4) but T4 is inactive and has to be converted to triiodothyronine (T3). This occurs throughout the body. It is T3 that the pituitary senses and if T3 levels are too high the pituitary stops putting out TSH, the thyroid stops working and the thyroid levels come back down to normal. If the T3 levels are too low the pituitary secretes more TSH and the thyroid starts releasing thyroid hormone again bringing the levels back up to normal.
TSH - measuring the setting for Cruise Control
Most of the causes of abnormal thyroid function occur within the thyroid itself and not the pituitary.
Sometimes the thyroid is stimulated by antibodies (Graves' disease) produced by the immune cells within the thyroid, and the TSH levels as a result are low. Other times the thyroid may be blocked or destroyed by antibodies (Hashimoto's Thyroiditis) and the TSH levels become elevated. The TSH level in the blood is the most sensitive indicator of these common causes of change in thyroid function.
In addition new assays for TSH can measure very low levels and are very reliable. Consequently the measurement of TSH has become the main screening test for thyroid dysfunction. A slight increase in thyroid hormone levels (mainly T3) quickly decreases the TSH level. A slight decrease quickly causes the TSH level to become elevated. Very occasionally changes in thyroid function are due to changes in pituitary function.
An underactive pituitary results in decreased TSH, decreased stimulation of the thyroid and decreased thyroid levels. A pituitary tumour that secretes TSH results in increased TSH levels, increased stimulation of the thyroid and increased thyroid levels. Measuring TSH in pituitary problems could, therefore, lead to the wrong diagnosis.
This rarely causes a problem though, because a high TSH due to a pituitary problem will be associated with clinical features of an overactive thyroid, and a low TSH due to a pituitary problem will be associated with clinical features of an underactive thyroid. In addition when TSH levels are abnormal, free T4 and free T3 are measured and help make the right diagnosis.
Causes of Fatigue
Changes in thyroid function typically cause fatigue. An underactive thyroid results in a general decrease in the activity of the body including the brain which would rather sleep.
An overactive thyroid initially may cause an increase in energy but the energy wasted in the process results in a decrease in total energy stores including the loss of protein and this eventually results in fatigue and loss of stamina and strength.
There are, however, many other causes of fatigue. Anemias of which there are many causes result in decreased oxygen delivery to cells throughout the body and thus fatigue.
Any chronic disease affecting the heart, kidneys, gut, and other organs can result in fatigue. Overwork, lack of sleep, depression, and boredom all sap a person's energy and result in fatigue.
These latter factors are probably the commonest causes of fatigue and certainly more common than changes in thyroid function.
Taking too much thyroid hormone may initially help the fatigue caused by these other disorders but in the long term the fatigue usually returns and too much thyroid hormone can result in a loss of bone mass (osteoporosis) and heart problems (irregular rhythms and heart failure).
Causes of Weight Gain
A decrease in thyroid function results in a decrease in the consumption of energy and as a result more energy is available to be stored. Weight gain is, therefore, typical of an underactive thyroid. There are many other causes for weight gain.
The main cause for weight gain, however, is still not understood. In North America almost everyone eats more calories than needed each day for normal metabolism of the cells. Fortunately most of us can waste these extra calories probably by burning them off in the form of heat.
People who start to put on weight lose the mechanism for wasting extra calories. If any extra calories are consumed beyond what is needed, and this may be quite small, the extra calories can only be stored and the weight increases.
People who are overweight often eat significantly less than those who are lean and yet still gain because they can't waste any extra calories. Taking thyroid hormone will help someone who is hypothyroid lose weight.
Taking too much thyroid hormone will usually cause anyone to burn off or waste calories and lose weight but much of the weight lost will be protein and result in osteoporosis and problems with the heart. When the thyroid hormone is stopped or reduced to normal amounts the weight will increase again.
Some individuals, who have been hyperthyroid but have been treated and now have normal thyroid levels, experience more difficulty keeping their weight down as compared to before they ever had a thyroid problem.
Somehow too much thyroid hormone for a period of time may permanently impair an individual's ability to waste extra calories and the weight tends to increase even though the thyroid levels are normal. This applies to individuals who have been hyperthyroid because of a thyroid problem such as Graves' disease and those individuals who take too much thyroid hormone over a long time.
Because of this and the long-term side effects of taking too much, thyroid hormone is not a good way to lose weight.
The safest approach is lifestyle modification that results in decreased caloric intake by changing eating habits and increased expenditure of calories by exercising more. Even though weight control may be more difficult after being hyperthyroid, it is still quite possible.
Is the thyroid why I am so tired and can't lose weight?
Mrs. Smith has many reasons to be tired. Having two fulltime jobs and sole responsibility for three children would be enough to make anyone tired.
Even though she did not have other symptoms and signs of an underactive thyroid it was still quite reasonable, with her family history, to measure the TSH level. The normal result though excludes a thyroid problem as a cause for her fatigue.
Mr. Jones lost weight when his thyroid was overactive. After he was treated and his thyroid became underactive he again put on weight.
Unfortunately, he experienced even more difficulty keeping his weight down than he had prior to having any thyroid problem even when his thyroid levels were brought back to normal.
Although this might in part be due to a permanent effect of being hyperthyroid on his ability to waste extra calories, it is not due to a current lack of thyroid hormone since his TSH is normal.
Taking more thyroid hormone might help him lose weight but much of the weight loss will be protein and he will increase his risks for osteoporosis and heart problems.
In addition taking too much thyroid hormone may make it even more difficult for him to lose weight if the dose of thyroxine is decreased to normal amounts again.
Changes in thyroid function can cause fatigue and changes in weight. Although thyroid problems may affect up to 8% of women and 1% of men, there are still many other more common causes for these symptoms.
It is relatively simple and inexpensive, however, to rule out thyroid problems as a cause for these symptoms by measuring TSH in the blood. A normal TSH excludes thyroid problems as causes for fatigue and weight gain and individuals can be reassured that their cruise control is functioning just fine.
British Thyroid Foundation - patient-led charitable organisation
Brittish Thyroid Association - a non-profit making Society
The Hormone Foundation - resource for hormone-related conditions
Surviving Thyroid Cancer
Cancer Research UK
P.O. Box 123
Lincoln's Inn Fields
London WC2A 3PX
tel: (Supporter Services) 020 7121 6699
tel: (Switchboard) 020 7242 0200
fax: 020 7269 3100
Registered charity no. 1089464
Health Tip: Watch your body pH
Ozone and health
Chernobyl accident effects
Diabetes could cripple health budgets
Memory and memory loss
Fat man of Europe
Is sex necessary