About the Thyroid

The thyroid is a small gland, shaped like a butterfly or bowtie, located in the lower part of your neck, in front of your windpipe. Like other glands, the thyroid secretes hormones. The main hormones released by the thyroid -- triiodothyronine, abbreviated as T3, and thyroxine, abbreviated as T4 -- deliver energy to cells of the body. Thyroid hormones control your metabolism -- the process by which oxygen and calories are converted to energy for use by your cells and organs.

When your thyroid works normally, it produces and secretes the amount of T4 and T3 necessary to keep various bodily functions moving at their proper pace. The thyroid frequently is a common target of disease or dysfunction. It's estimated that more than 200 million people at minimum worldwide have thyroid disease, and some experts estimate that anywhere from 30 to 59 million Americans have thyroid disease.

The thyroid requires iodine -- usually ingested through the diet -- to produce thyroid hormone. Thyroid problems are particularly common in areas covered at one time by glaciers, where iodine is not present in the soil and in foods. In many of these countries, an enlarged thyroid, known as goiter, is seen in as many as one in five people, and is usually due to iodine deficiency. According to the World Health Organization, iodine deficiency is the world's most prevalent -- yet easily preventable -- cause of brain damage. It affects more than 740 million people worldwide -- 13% of the world's population. As many as an additional 30% of the population worldwide is at risk of iodine deficiency-related problems. In the U.S., use of iodized salt helped reduce iodine deficiency, but as many as 20% of Americans are still iodine-deficient.

When it occurs during pregnancy, mild iodine deficiency in a pregnant mother can cause cognitive and developmental problems in her children that may reduce their IQ by as much as 15 IQ points. But serious iodine deficiency in a pregnant woman can cause stillbirth, miscarriage, and in particular, a congenital abnormality known as cretinism in her child. Cretinism is a serious, irreversible condition often involving severe mental retardation, and is most common in iodine-deficient areas of Africa and Asia.

In the U.S., the majority of thyroid conditions is due to autoimmune disease, and in particular, Hashimoto's disease. Thyroid disease prevalence increases with age and is more common in women. A woman in the U.S. faces as high as a one in five chance of developing a thyroid problem during her lifetime, and generally, women are seven to eight times more likely than men to develop thyroid conditions.

Besides iodine deficiency and being a woman, there are a number of risk factors for thyroid disease. These include genetics and heredity, personal or family history of endocrine or autoimmune disease, infection, exposure to goitrogenic foods, cigarette smoking, pregnancy, certain drugs, particular chemical exposures, radiation exposure, and many other factors.

The most common health issues affecting the thyroid include:

• Hypothyroidism -- the condition whereby the thyroid is not producing enough -- or any -- thyroid hormone. Congenital hypothyroidism is present at birth, usually due to a missing or poorly developed thyroid gland.
• Hyperthyroidism -- the condition whereby the thyroid is producing too much thyroid hormone
• Autoimmune Thyroid Disease -- Hashimoto's Disease is an autoimmune disease that typically causes hypothyroidism. Graves' Disease typically causes hyperthyroidism.
• Goiter -- enlargement of the thyroid
• Nodules -- lumps or masses in the thyroid, benign
• Thyroiditis -- viral, autoimmune, or post-pregnancy inflammation of the thyroid, causing hyperthyroidism, hypothyroidism, or alternating hyperthyroidism and hypothyroidism after pregnancy, sometimes temporary or transient.
• Thyroid cancer -- cancerous nodules or tissue in the thyroid

NEXT: Thyroid Diseases and Conditions