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What is hypothyroidism?

Hypothyroidism is a condition where your thyroid gland doesn’t produce enough thyroid hormones to keep your metabolism and other bodily processes functioning at a good level.

Your thyroid gland is a small butterfly-shaped gland that is located on the front part of your lower neck. It controls your metabolism, which is essentially how the cells in your body use energy gained from food. Low thyroid levels cause your metabolism to become sluggish, which in turn lowers your body temperature, slows your heart rate, and decreases the rate in which you burn calories.

People with hypothyroidism may be told they have an underactive thyroid. Hypothyroidism may also be known as Hashimoto's disease.

What causes hypothyroidism?

Hypothyroidism may be caused by several different factors which result in the thyroid gland no longer producing enough hormones, such as:

  • Autoimmune disorders, specifically Hashimoto's thyroiditis. This is when the cells of your immune system slowly attack the cells of the thyroid gland, decreasing the production of thyroid hormones
  • Congenital disease. Some babies are born with a defective thyroid gland or no thyroid gland at all
  • Iodine deficiency. Iodine is a trace mineral iodine that is essential for the production of thyroid hormones. It is found primarily in seafood, seaweed, plants grown in iodine-rich soil and iodized salt. In some parts of the world iodine deficiency is common
  • Over-correction with radioactive iodine or anti-thyroid medications. People who have hyperthyroidism (high thyroid levels) are often treated with radioactive iodine or anti-thyroid medications that aim to get thyroid functioning normally. However, treatment may be too effective, resulting in permanent hypothyroidism
  • Pituitary gland disorders that decrease the production of thyroid-stimulating hormone (TSH) in the pituitary gland
  • Pregnancy
  • Thyroid surgery. Removal of part or the whole thyroid gland decreases or stops thyroid hormone production
  • Radiation therapy to treat cancer of the head or neck can sometimes affect a part of the thyroid gland
  • Some medications such as amiodarone or lithium

What are the symptoms of hypothyroidism?

Symptoms of hypothyroidism can be vague and may be confused with other conditions.

More common symptoms include:

  • Greater sensitivity to cold
  • A slow heart rate
  • Fatigue
  • Dry hair and hair loss
  • Dry skin
  • Unexplained weight gain or difficulty losing weight
  • Changes in the menstrual cycle
  • Constipation
  • Depression
  • Carpal tunnel syndrome
  • Swelling of the thyroid gland

One in every 3000 to 4000 babies are born with hypothyroidism. This is called congenital hypothyroidism and occurs because the thyroid gland does not develop or function properly. It is usually permanent and life-long.

Symptoms may not be obvious and may include:

  • Poor feeding
  • Cold hands and feet
  • Extreme sleepiness
  • A weak or hoarse cry
  • Constipation
  • Little or no growth
  • Poor muscle tone (floppy infant)
  • Persistent jaundice
  • Puffy face or a swollen tongue
  • Stomach bloating

How is hypothyroidism diagnosed?

Make an appointment with your doctor if you suspect your thyroid levels are low, or if your baby has symptoms of hypothyroidism.

Your doctor will examine your neck and inspect your thyroid gland which may be enlarged. Your heart rate may be checked as well as your knee and ankle reflexes to see if they respond more slowly.

Blood tests that measure the levels of thyroid hormones and serum TSH will be ordered, and possibly other tests such as those for cholesterol which is often abnormal in people with hypothyroidism. Your doctor will make a diagnosis based on the results of all these tests.

How is hypothyroidism treated?

Hypothyroidism is treated by replacing the missing thyroid hormones with oral synthetic thyroid hormones, such as levothyroxine, liothyronine, or liotrix.

Regular blood tests are needed to make sure that you are taking the right dose for your body, as the dosage can vary among people. Pregnant women may need higher dosages of thyroid hormones during pregnancy, and some foods and medications can affect the absorption and levels in the blood of replacement thyroid hormones.