Hypothyroidism | Causes & Risk Factors


What causes hypothyroidism?

The most common cause of hypothyroidism is an autoimmune disease called Hashimoto’s thyroiditis. Normally, antibodies produced by the immune system help protect the body against viruses, bacteria and other foreign substances. An autoimmune disease is when your immune system produces antibodies that attack your body's tissues and/or organs. With Hashimoto’s thyroiditis, antibodies attack the thyroid and keep it from producing enough hormones.

Other common causes of hypothyroidism include:

  • Treatment for hyperthyroidism, the condition in which the body produces too much thyroid hormone
  • Radiation therapy
  • Thyroid surgery
  • Certain medicines

Some less common causes of hypothyroidism include:

  • Congenital disease: About 1 in 3,000 infants in the United States are born with a defective thyroid or no thyroid at all. Most states require doctors to screen newborns for thyroid problems.
  • Pituitary disorder: The pituitary gland produces a thyroid-stimulating hormone, which tells the thyroid gland how much thyroid hormone to produce. A pituitary disorder may keep the pituitary gland from producing the right amount of thyroid-stimulating hormone.
  • Pregnancy: Some women develop hypothyroidism during or after pregnancy because their bodies produce antibodies that attack the thyroid gland. If it is not treated, hypothyroidism can jeopardize the health of both mother and baby.
  • Iodine deficiency: Iodine is a mineral used by the body to make thyroid hormones. Iodine deficiency can keep the body from being able to make enough thyroid hormone. In the United States, table salt has iodine added to it to make sure everyone gets enough.

You have an increased risk of developing hypothyroidism if you:

  • Have a close relative who has an autoimmune disease
  • Have been treated with radioactive iodine or anti-thyroid medicines
  • Have received radiation therapy to your neck or upper chest
  • Have had thyroid surgery in the past

Written by familydoctor.org editorial staff

Reviewed/Updated: 03/14
Created: 09/07