Risk Factors and Causes

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Who is likely to develop hypothyroidism?

Women are much more likely than men to develop hypothyroidism. The disease is also more common among people older than age 60. The American Thyroid Association recommends that adults, particularly women, have a blood test to detect thyroid problems every 5 years starting at age 35.

Certain factors can increase a person’s chances of developing thyroid disorders. Individuals may need more regular testing if they

  • have had a thyroid problem before, such as goiter or thyroid surgery
  • have a family history of thyroid disease
  • have other autoimmune diseases including Sjögren’s syndrome, pernicious anemia, type 1 diabetes, rheumatoid arthritis, or lupus
  • have Turner syndrome, a genetic disorder that affects girls and women
  • are older than 60
  • have been pregnant or delivered a baby within the past 6 months
  • have received radiation to the thyroid or to the neck or chest

Getting tested routinely helps uncover thyroid problems—especially subclinical problems. Subclinical means a person has no apparent symptoms. Some doctors treat subclinical hypothyroidism immediately; others prefer to leave it untreated but monitor their patients for signs that the condition is worsening.


What causes hypothyroidism?

Hypothyroidism has several causes, including

  • Hashimoto’s disease
  • thyroiditis, or inflammation of the thyroid gland
  • congenital hypothyroidism, or hypothyroidism that is present at birth
  • surgical removal of part or all of the thyroid gland
  • radiation treatment of the thyroid
  • some medications

Less commonly, hypothyroidism is caused by too much or too little iodine in the diet or by abnormalities of the pituitary gland.

Hashimoto’s Disease

Hashimoto’s disease, also called chronic lymphocytic thyroiditis, is the most common cause of hypothyroidism in the United States. Hashimoto’s disease is an autoimmune disorder, which means the body’s immune system, which normally protects the body by attacking foreign organisms, acts against its own healthy cells and tissues. In Hashimoto’s disease, the immune system makes antibodies that attack cells in the thyroid and interfere with their ability to produce thyroid hormone.


Thyroiditis causes stored thyroid hormone to leak out of the inflamed thyroid gland. At first, the leakage raises hormone levels in the blood, leading to hyperthyroidism that lasts for a month or two. Most people then develop hypothyroidism before the thyroid is completely healed. Several types of thyroiditis can lead to hypothyroidism:

·         Subacute thyroiditis. This condition involves painful inflammation and enlargement of the thyroid. Doctors aren’t sure what causes subacute thyroiditis, but it may be related to a viral or bacterial infection. The condition usually goes away on its own in a few months.

·         Postpartum thyroiditis. Some women who have been pregnant develop postpartum thyroiditis within a few months of giving birth. In some women, the thyroid does not heal and their hypothyroidism is permanent. Postpartum thyroiditis is believed to be an autoimmune condition.

·         Silent thyroiditis. This type of thyroiditis is called “silent” because it is painless, as is postpartum thyroiditis, even though the thyroid may be enlarged. Silent thyroiditis is probably an autoimmune condition and sometimes develops into permanent hypothyroidism.

Congenital Hypothyroidism

Some babies are born with a thyroid that is not fully developed or does not function properly. If untreated, congenital hypothyroidism can lead to mental retardation and growth failure. Most newborns in the United States are screened for hypothyroidism, and early treatment can prevent these complications.

Surgical Removal of the Thyroid

Part or all of the thyroid gland may be surgically removed as a treatment for

  • hyperthyroidism, when the thyroid makes too much thyroid hormone
  • a large goiter, which is an enlarged thyroid gland that may cause the neck to appear swollen and can interfere with normal breathing and swallowing
  • thyroid nodules, which are lumps in the thyroid that can produce excess thyroid hormone
  • thyroid cancer

When part of the thyroid is removed, the remaining part may produce normal amounts of thyroid hormone, but some people who have this surgery develop hypothyroidism. Removal of the entire thyroid always results in hypothyroidism.

Radiation Treatment of the Thyroid

Radioactive iodine, a common treatment for hyperthyroidism, gradually destroys the cells of the thyroid. Almost everyone who receives radioactive iodine treatment eventually develops hypothyroidism. People with Hodgkin’s disease, other lymphomas, and head or neck cancers are treated with radiation, which can also damage the thyroid.


Some drugs can interfere with thyroid hormone production and lead to hypothyroidism. These drugs include

  • amiodarone, a heart medication
  • interferon alpha, a cancer medication
  • lithium, a bipolar disorder medication
  • interleukin-2, a kidney cancer medication

Source:National Endocrine and Metabolic Diseases Information Service