Many factors can affect the functioning of the thyroid gland and cause thyroid disorders.

For example, imbalances in iodine levels (either a deficiency or a surplus) may lead to goiter, hypothyroidism or hyperthyroidism. Viral infections cause some types of thyroiditis. There are also autoimmune disorders, such as Hashimoto’s thyroiditis, which causes hypothyroidism, and Graves' disease, which causes hyperthyroidism.

Use of certain medications sometimes causes thyroid disorders. This may include amiodarone (antiarrhythmic heart drug), lithium (bipolar disorder drug), and interferon alpha and interleukin-2 (cancer drugs).

Surgical removal of part or all of the thyroid gland, or damage done to the gland as a part of treatment for other conditions (e.g., using radioactive iodine to treat goiter, hyperthyroidism or thyroid cancer) may cause hypothyroidism. Damage to the pituitary gland, which communicates with the thyroid gland, may also cause some types of thyroid disorders.

Women who are pregnant may produce antibodies to their own thyroid gland that can lead to hypothyroidism and increases the risk of miscarriage, premature delivery and preeclampsia, a serious disorder of late pregnancy that involves high blood pressure, swelling and protein in the urine. After giving birth, women can experience a temporary thyroid disorder known as postpartum thyroiditis.

>The cause of many cases of thyroid disorders remains unknown.

Risk factors that put a person at an increased risk of developing thyroid disorders include:

• Sex. Women develop thyroid disorders more frequently than men.
  
  
• Age. Many thyroid disorders are more likely to affect people over the age of 40. Hypothyroidism is particularly common after age 60.
  
  
• Family history. People with a family history of thyroid disorders may be more likely to develop thyroid disorders.
  
  
• Down syndrome. Hypothyroidism, along with an enlarged thyroid gland, occurs more frequently in people born with Down syndrome.