Underactive thyroid
What is an underactive thyroid?
If your thyroid gland is underactive, it doesn't make enough hormones. These hormones control how much energy your body uses.
An underactive thyroid can make you feel tired and depressed. You may also put on weight or have dry skin or hair. But you
can have an underactive thyroid without noticing any symptoms.
Treatment for an underactive thyroid works well. You can take hormone pills to replace the hormones your body isn't making.
Doctors call an underactive thyroid hypothyroidism.
- An underactive thyroid is common in women. About 1 in 10 women over 60 have a mild form of the condition.
Source:
Canaris GJ, Manowitz NR, Mayor G, et al.
The Colorado thyroid disease prevalence study.
Archives of Internal Medicine. 2000; 160: 526-533.
1Source:
Hak AE, Pols HA, Visser TJ, et al.
Subclinical hypothyroidism is an independent risk factor for atherosclerosis and myocardial infarction in elderly women: the Rotterdam Study.
Annals of Internal Medicine. 2000; 132: 270-278.
2 - The most common cause of an underactive thyroid is when the body's immune system attacks its own thyroid gland.
Source:
Hak AE, Pols HA, Visser TJ, et al.
Subclinical hypothyroidism is an independent risk factor for atherosclerosis and myocardial infarction in elderly women: the Rotterdam Study.
Annals of Internal Medicine. 2000; 132: 270-278.
2 - You can take pills to replace the hormones your thyroid should be making. You'll usually need to take these for the rest of your life.
Source:
Brix TH, Kyvik KO, Hegedus L.
A population-based study of chronic autoimmune hypothyroidism in Danish twins.
Journal of Clinical Endocrinology and Metabolism. 2000; 85: 536-539.
Brix TH, Kyvik KO, Hegedus L.
A population-based study of chronic autoimmune hypothyroidism in Danish twins.
Journal of Clinical Endocrinology and Metabolism. 2000; 85: 536-539.
There are two thyroid hormones.
Your thyroid gland sits just below your voice box, in front of your windpipe.
- The main one is thyroxine, also called T4. It's made by your thyroid gland and pumped into your blood.
- The second hormone is triiodothyronine. It's sometimes called T3. Your
liver
Your liver is a large organ that sits on the right side of your body, just below your rib cage. It does several important things, including processing and storing nutrients from food, and breaking down chemicals, such as alcohol.liver andkidney
Your kidneys are organs that filter your blood to make urine. You have two of them, on either side of your abdominal cavity, toward your back.kidneys make T3 out of T4.
Problems with your thyroid can make it underactive or overactive. Here, we're looking at an underactive thyroid. This is called hypothyroidism.
A hormone called thyroid-stimulating hormone (TSH) decides how much of the thyroid hormones your body needs. TSH is made by your pituitary gland, which is in your brain.
- If the amount of T4 and T3 in your blood drops too low, your pituitary gland releases more TSH. This tells your thyroid to make more hormones.
- If the amount of T4 and T3 is too high, your pituitary gland stops releasing TSH. Your thyroid then stops making T3 and T4.
If you have symptoms, such as feeling tired or putting on weight, and blood tests show you have an underactive thyroid, doctors
call your condition overt hypothyroidism.
But you may not notice any symptoms. If you don't have symptoms, but blood tests show you have a slightly underactive thyroid,
your doctor may say you have mild hypothyroidism.
- A problem with the thyroid gland itself. This is the most common cause.
- Something else, such as a tumor, stops the pituitary gland working properly. So the pituitary gland doesn't produce the hormones that encourage the thyroid to work. This is less common.
This is the most common reason for your thyroid to stop working properly. It means your body's
immune system, which normally helps your body fight infections, attacks your thyroid gland. If you have this type of hypothyroidism, your
thyroid gland may grow larger. But not everyone gets this.
immune system
The immune system is made up of the parts of the body that are devoted to fighting infection. The body is constantly being threatened by infections from things like bacteria, viruses and parasites. The immune system fights these infections in different ways. At the microscopic level, the immune system uses antibodies and white blood cells, which travel in the blood and target infectious agents, such as bacteria. These microscopic parts of the immune system either kill the infectious agent directly, or take it to other parts of the body, like the spleen, where it can be dealt with. The lymph nodes are another important part of the immune system. Within them, white blood cells filter through the foreign material that has entered the blood, to see if there are any infections. When you have a swollen gland during a cold, this is actually a lymph node that is reacting to the infection. Unfortunately, it is possible for the immune system to become confused and to use its destructive powers to target healthy parts of the body. Diseases that result from this type of situation are called autoimmune diseases.
The immune system is made up of the parts of the body that are devoted to fighting infection. The body is constantly being threatened by infections from things like bacteria, viruses and parasites. The immune system fights these infections in different ways. At the microscopic level, the immune system uses antibodies and white blood cells, which travel in the blood and target infectious agents, such as bacteria. These microscopic parts of the immune system either kill the infectious agent directly, or take it to other parts of the body, like the spleen, where it can be dealt with. The lymph nodes are another important part of the immune system. Within them, white blood cells filter through the foreign material that has entered the blood, to see if there are any infections. When you have a swollen gland during a cold, this is actually a lymph node that is reacting to the infection. Unfortunately, it is possible for the immune system to become confused and to use its destructive powers to target healthy parts of the body. Diseases that result from this type of situation are called autoimmune diseases.
We don't know why your immune system can attack your thyroid gland. But your genes (the genetic material you inherit from
your parents) could be a cause. You're more likely to get this type of hypothyroidism if a brother or sister has it.
3
Source:
Brix TH, Kyvik KO, Hegedus L.
A population-based study of chronic autoimmune hypothyroidism in Danish twins.
Journal of Clinical Endocrinology and Metabolism. 2000; 85: 536-539.
Brix TH, Kyvik KO, Hegedus L.
A population-based study of chronic autoimmune hypothyroidism in Danish twins.
Journal of Clinical Endocrinology and Metabolism. 2000; 85: 536-539.
Your thyroid can be damaged by surgery or
X-ray treatment. This could mean there isn't enough healthy gland left to make the hormones your body needs. You might have surgery
to remove a growth or cancer near your thyroid.
X-ray
X-rays are pictures taken of the inside of your body. They are done by passing very small amounts of radiation through your body and onto film. X-rays can also be used as a treatment, such as in radiation therapy for cancer.
X-rays are pictures taken of the inside of your body. They are done by passing very small amounts of radiation through your body and onto film. X-rays can also be used as a treatment, such as in radiation therapy for cancer.
If you have an overactive thyroid (hyperthyroidism) you might have radiation treatment to destroy some of your thyroid gland. If too much tissue is destroyed
by accident, it can make your thyroid underactive.
Some medicines can stop your thyroid gland from working properly. Drugs that can do this include lithium (used to treat some kinds of depression), amiodarone (used to treat abnormal heart rhythms) and interferon (used to treat hepatitis).
About 5 in 100 pregnant women get an underactive thyroid after they have their baby.
4 It usually clears up by itself after a few months.
Source:
Braunwald E, Fauci AS, Kasper DL (editors).
Harrison's principles of internal medicine.
15th edition. McGraw-Hill, New York, U.S.A.; 2001.
Braunwald E, Fauci AS, Kasper DL (editors).
Harrison's principles of internal medicine.
15th edition. McGraw-Hill, New York, U.S.A.; 2001.
You're more likely to get an underactive thyroid if you have another condition where your immune system attacks part of your
body. This is called autoimmune disease. Addison's disease (a disease of the adrenal gland) and vitiligo (where you get white patches on your skin) are examples
of autoimmune disease.
4
Source:
Braunwald E, Fauci AS, Kasper DL (editors).
Harrison's principles of internal medicine.
15th edition. McGraw-Hill, New York, U.S.A.; 2001.
Braunwald E, Fauci AS, Kasper DL (editors).
Harrison's principles of internal medicine.
15th edition. McGraw-Hill, New York, U.S.A.; 2001.
Your thyroid gland needs iodine from your food to make hormones. But in some parts of the world, there's not enough iodine in the soil, water and food supply. This can make people's thyroid glands become diseased and grow bigger. An enlarged thyroid
is called a goiter. This problem is more common in developing countries than the West. It can be treated by adding iodine to flour or salt.
Sources for the information on this page:
- Canaris GJ, Manowitz NR, Mayor G, et al.The Colorado thyroid disease prevalence study.Archives of Internal Medicine. 2000; 160: 526-533.
- Hak AE, Pols HA, Visser TJ, et al.Subclinical hypothyroidism is an independent risk factor for atherosclerosis and myocardial infarction in elderly women: the Rotterdam Study.Annals of Internal Medicine. 2000; 132: 270-278.
- Brix TH, Kyvik KO, Hegedus L.A population-based study of chronic autoimmune hypothyroidism in Danish twins.Journal of Clinical Endocrinology and Metabolism. 2000; 85: 536-539.
- Braunwald E, Fauci AS, Kasper DL (editors).Harrison's principles of internal medicine.15th edition. McGraw-Hill, New York, U.S.A.; 2001.
This information was last updated on Apr 21, 2009
This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment.
© BMJ Publishing Group Limited 2009. All rights reserved.
© BMJ Publishing Group Limited 2009. All rights reserved.
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