Causes of Underactive Thyroid

When a person is diagnosed with an underactive thyroid, the cause is often attributed to something that affects the thyroid gland directly, such as thyroiditis, surgery to remove part or all of the gland, or radiation treatment. This is called primary hypothyroidism. In other cases, a child may be born with an underactive thyroid. Medications used to treat conditions like bipolar disorder and kidney cancer also can cause hypothyroidism.

What Causes an Underactive Thyroid?

An underactive thyroid can be caused by anything that affects the thyroid gland, pituitary gland, hypothalamus, or the messengers that communicate between these glands. Most often, the issue is with the thyroid itself (this is known as primary hypothyroidism).

If the problem is with the pituitary gland, it is known as secondary hypothyroidism. Tertiary hypothyroidism is diagnosed when the problem is with the hypothalamus.

In about 95 percent of cases, an underactive thyroid is the result of a problem within the thyroid itself (primary hypothyroidism).

Specific Causes of Primary Hypothyroidism

Some possible underactive thyroid causes that are attributable to problems with the thyroid gland include:

Hashimoto's thyroiditis
Surgical removal of part or all of the thyroid gland
Radiation treatment of the thyroid
Thyroiditis (inflammation of the thyroid gland)
Congenital hypothyroidism (an underactive thyroid that is present at birth)
Certain medications
Iodine deficiency or excess.

Hashimoto's Thyroiditis

Hashimoto's thyroiditis, also called chronic lymphocytic thyroiditis or chronic autoimmune thyroiditis, is the most common cause of an underactive thyroid in the United States. This is a type of autoimmune thyroid disease in which the immune system attacks and destroys the thyroid gland.

The thyroid helps set the rate of metabolism, which is the rate at which the body uses energy. Hashimoto's stops the gland from making enough thyroid hormones for the body to work the way it should. It is more common in older women. It is also the most common cause of hypothyroidism in children, being diagnosed as early as one year of age.

There is some evidence that Hashimoto's thyroiditis can have a hereditary link. Thus, if autoimmune diseases in general run in your family, you are at a higher risk of developing one yourself.

Causes of Underactive Thyroid Article Continues on Next Page >