Also called overactive thyroid, hyperthyroidism affects about 1 percent of the population -- it occurs when too much thyroid hormone is produced by the thyroid gland. Graves' disease is the most common cause, but hyperthyroidism can also occur due to thyroid nodules, thyroiditis, and other conditions. Symptoms will vary, but may include fatigue, increased sweating, and weight loss, among others.
What Is Hyperthyroidism?
Hyperthyroidism (also known as an overactive thyroid) is a condition that occurs when the thyroid gland makes more thyroid hormone than the body needs. It is sometimes called thyrotoxicosis, the technical term for too much thyroid hormone in the blood.
Hyperthyroidism affects about 1 percent of the population. Women are much more likely to develop this condition than men, and the risk increases with age. About 5 percent of women over the age of 60 have been diagnosed with hyperthyroidism (see Hyperthyroidism Risk Factors).
What Is the Thyroid Gland?
The thyroid is a butterfly-shaped gland that is about two inches in length. It is located in the front of the neck below the larynx (voice box) and above the clavicles (collarbones). It is made up of two lobes, one on either side of the windpipe.
The thyroid is one of a group of glands that are part of the endocrine system. The endocrine glands produce, store, and release hormones into the bloodstream that travel through the body and direct the activity of the body's cells. Thyroid hormones regulate metabolism, which is the way the body uses energy, and they affect nearly every organ in the body.
The thyroid gland makes two thyroid hormones: triiodothyronine (T3) and thyroxine (T4). Thyroid hormones affect metabolism, brain development, breathing, heart and nervous system functions, body temperature, muscle strength, skin dryness, menstrual cycles, weight, and cholesterol levels.
Thyroid hormone production (both T3 and T4) is regulated by thyroid-stimulating hormone (TSH), which is made by the pituitary gland. Located in the brain, the pituitary gland is the "master gland" of the endocrine system.
Hollowell JG, Staehling NW, Flanders WD, et al. Serum TSH, T-4, and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III). J Clin Endocrinol Metab. 2002;87:489.
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