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Hypothyroidism means that the thyroid gland doesn't make enough thyroid hormone. This hormone controls the way your body uses energy. The thyroid is a butterfly-shaped gland in the front of your neck.
Having a low level of thyroid hormone affects your whole body. It can make you feel tired and weak. If it isn't treated, it can raise your cholesterol levels. During pregnancy, untreated hypothyroidism can harm your baby. But low thyroid levels can be treated with medicine that can help you feel like yourself again.
People of any age can get hypothyroidism, but older adults are more likely to get it. Women age 60 and older have the highest risk. You are more likely to get the disease if it runs in your family.
In Canada, the most common cause of hypothyroidism is Hashimoto's thyroiditis. It causes the body's immune system to attack thyroid tissue. As a result, the gland can't make enough thyroid hormone. Worldwide, iodine deficiency is the number one cause of hypothyroidism.
If you have low thyroid levels, you may feel tired, weak, or depressed. Other symptoms include dry skin, brittle nails, not being able to stand the cold, constipation, memory problems, and heavy or irregular menstrual periods. Symptoms occur slowly over time. You might not notice them or might mistake them for normal aging.
To diagnose hypothyroidism, your doctor will first ask you about your past health problems and do a physical examination. If your doctor thinks you have the condition, a simple blood test can show if your thyroid hormone level is too low.
Hypothyroidism is treated with thyroid pills. Your symptoms will probably go away within a few months. But you will likely need to keep taking the pills. You will also need regular follow-up visits to make sure you have the right dose. If your condition is mild, you may not need treatment right away.
In Canada, the most common cause is Hashimoto's thyroiditis.
Worldwide, iodine deficiency is the number one cause of low thyroid levels.
Other common causes include:
Less common causes include:
Many things may increase your risk for hypothyroidism. These include:
Older adults are more likely to develop hypothyroidism than younger people. And women are more likely than men to develop thyroid disease.
Hypothyroidism tends to run in families.
Thyroid disease, an enlarged thyroid (goiter), and surgery or radiation therapy to treat thyroid problems increase the likelihood of having hypothyroidism in the future.
Type 1 diabetes, vitiligo (an autoimmune disease that causes patches of light skin), pernicious anemia, and leukotrichia (premature grey hair) are seen more often in people who have hypothyroidism.
This is rare in Canada but common in areas where iodine is not added to salt, food, and water.
Some medicines can interfere with normal thyroid function, particularly lithium or amiodarone.
Low thyroid levels can cause many different symptoms, including:
Symptoms occur slowly over time. At first you might not notice them, or you might mistake them for normal aging.
Although rare, hypothyroidism can occur in infants, children, and teens. In infants, symptoms include a poor appetite and choking on food. Symptoms may also include dry, scaly skin. In children and teens, symptoms include behaviour problems and changes in school performance. Children and teens may gain weight but have a slowed growth rate. Teens may have delayed puberty and look much younger than their age.
Symptoms of hypothyroidism during and after pregnancy include fatigue, weight loss, dizziness, depression, and memory and concentration problems.
Hypothyroidism caused by Hashimoto's thyroiditis sometimes goes away on its own. More often it causes gradual loss of thyroid function. Symptoms may develop slowly and be mild. But symptoms usually grow worse, and health problems may develop over time.
If untreated, hypothyroidism may lead to myxedema. This condition causes swelling of tissues, increased fluid around the heart and lungs, slowed muscle reflexes, and a slowed ability to think. In rare cases, it can cause a coma which can be life-threatening.
People with mild (subclinical) hypothyroidism have only slightly abnormal thyroid blood test results and often do not have obvious symptoms or health problems. Some people who have mild hypothyroidism regain normal thyroid function.
If your thyroid gland has been removed during surgery, hypothyroidism will occur within a few weeks. If you have been treated with radioactive iodine therapy, hypothyroidism may develop within a year. In these cases, thyroid function typically doesn't return.
Although rare, hypothyroidism can occur in infants and children. If hypothyroidism is treated within the first month of life, a child will grow and develop normally. Untreated hypothyroidism in infants can cause brain damage, leading to intellectual disability and developmental delays. In Canada, all children are tested for hypothyroidism at birth.
Intellectual disability usually does not occur if hypothyroidism develops after age 3. But untreated childhood hypothyroidism typically delays physical growth and sexual development, including the onset of puberty. Children may gain weight yet have a slowed growth rate.
Call 911 or other emergency services immediately if you or a person you know has hypothyroidism and has signs of myxedema coma, such as:
See your doctor if you have any symptoms that don't go away, including:
If you have one or two of the above symptoms that have not changed or have changed very little over a long period of time, it's less likely that the symptoms are caused by hypothyroidism. Consult your doctor.
Talk to a doctor if you are pregnant and have some of the above symptoms. Also talk to a doctor if you have hypothyroidism and are pregnant or are trying to become pregnant. Your dose of thyroid hormone medicine may need to be changed.
Watchful waiting is a wait-and-see approach. It's not a good choice for hypothyroidism that is causing symptoms. Treatment should start as soon as the condition is diagnosed.
Watchful waiting may be okay for certain adults with mild (subclinical) hypothyroidism whose blood tests show only small changes. Talk to your doctor about treatment and possible risks and benefits. Watch for any signs that your hypothyroidism is getting worse. Doctors often want people to have yearly thyroid function blood tests to check to see if thyroid hormone production is normal.
To diagnose hypothyroidism, your doctor will first ask you about your past health problems and do a physical examination. If your doctor thinks you have the condition, a simple blood test can show if your thyroid hormone level is too low. The blood tests used most often are:
If the results of the above tests aren't normal, you may have antithyroid antibody tests. These tests can tell if you have the autoimmune disease Hashimoto's thyroiditis. When you have this disease, your body's defence system attacks the thyroid gland.
Because hypothyroidism may cause problems with thinking and learning, most provinces test newborns for the condition. If your baby wasn't born in a hospital or if you think your baby may not have been tested, talk to your doctor.
The Canadian Task Force on Preventive Health Care does not recommend screening for hypothyroidism in adults who do not have symptoms. If you are pregnant or have had thyroid problems, talk to your doctor about screening.footnote 1
Thyroid hormone medicine is the only way to treat hypothyroidism. Your doctor will treat your low thyroid level with the thyroid pills levothyroxine. Usually, thyroid hormone medicine:
After you start treatment, you'll have regular visits with your doctor to see if you have the right dose of medicine. Getting too much or too little thyroid hormone can cause problems.
Thyroid hormone medicine does not cause side effects if you take the correct dose. Depending on its cause, people who have hypothyroidism may need treatment for the rest of their lives.
CitationsBirtwhistle R, et al. (2019). Recommendation on screening adults for asymptomatic thyroid dysfunction in primary care. Canadian Medical Association Journal, 191(46): E1274–E1280. DOI: 10.1503/cmaj.190395. Accessed online: May 1, 2020.
Current as of: February 27, 2023
Author: Healthwise StaffMedical Review: Kathleen Romito MD - Family MedicineE. Gregory Thompson MD - Internal MedicineMatthew I. Kim MD - Endocrinology
Current as of: February 27, 2023
Author: Healthwise Staff
Medical Review:Kathleen Romito MD - Family Medicine & E. Gregory Thompson MD - Internal Medicine & Matthew I. Kim MD - Endocrinology
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