About 1 percent of the population is affected by overactive thyroid, a condition that occurs when too much thyroid hormone is produced by the thyroid gland. The most common cause of high thyroid levels is Graves' disease, but the condition can also be caused by thyroid nodules, thyroiditis, and other conditions. Common symptoms include weight loss, fatigue, and increased sweating.
Overactive thyroid (known medically as hyperthyroidism) 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.
Overactive thyroid affects about 1 percent of the population. Women are much more likely to develop this condition than men. The risk also increases with age. About 5 percent of women over the age of 60 have been diagnosed with overactive thyroid (see Hyperthyroidism Risk Factors).
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 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.