What Is Hypothyroidism?

Millions of people suffer from some form of thyroid disease. The vast majority — approximately 80 percent — have an underactive thyroid, or what is called hypothyroidism. According to the AACE, hypothyroidism affects about 10 percent of all women and 3 percent of men. Studies suggest that approximately 13 million Americans are undiagnosed.

Several factors can cause the thyroid to reduce its production of thyroid hormone. Here in the United States, the most common cause of hypothyroidism is an autoimmune disorder called Hashimoto's thyroiditis, in which the body launches an internal attack on its own healthy thyroid tissues, destroying the gland's ability to produce thyroid hormone. Hypothyroidism is also more common with aging. By age sixty, 17 percent of all women and 9 percent of men will have an underactive thyroid.

Around the world, the condition is caused primarily by a deficiency of iodine, a mineral found in saltwater, that the body uses to produce thyroid hormone. But with the introduction of iodized salt in the United States in the 1920s, iodine deficiency is practically unheard of in this country.


Primary hypothyroidism refers to an underactive thyroid caused by a deficiency in thyroid hormone. Central hypothyroidism is a term that describes a reduction in thyroid hormone caused by problems with the pituitary gland. Although the causes differ, treatment is usually the same.

In some cases, hypothyroidism may be linked to other medical conditions or caused by a medication. For instance, people who have been treated with RAI to treat hyperthyroidism often develop hypothyroidism. Those who take medications such as lithium, prednisone, and propranolol are also vulnerable to hypothyroidism.

In addition, anyone who has undergone thyroid surgery, also called thyroidectomy, or radiation to the neck or upper chest is likely to develop an underactive thyroid.

Of course, not everyone who gets older or takes these medications will develop hypothyroidism. But your risk does go up if you have other risk factors, including:

  • A family history of thyroid problems

  • A personal history of endocrine disease, including diabetes

  • Illnesses or injuries involving the hypothalamus and/or the pituitary gland

  • A personal or family history of autoimmune illness

  • Recent pregnancy and delivery

  • Illnesses such as chronic fatigue immune deficiency syndrome or fibromyalgia

Regardless of what triggers an underactive thyroid, the end result is the same: hypothyroidism causes all your body functions to slow down. This total-body slowdown produces signs and symptoms that will eventually become apparent.

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