Hypothyroidism (underactive thyroid)

The thyroid gland is a small butterfly shaped gland that is located in the lower front of the neck just under the Adam's apple. The thyroid gland produces hormones that control the body's organ functions and metabolism (how the body uses and stores energy from foods eaten). Hypothyroidism is an underactive thyroid that is not producing enough of the thyroid hormone for the body to maintain a healthy metabolism. Anyone can develop hypothyroidism, but it occurs mostly in women over 40 and the risk increases with age. Hypothyroidism is the most common thyroid disorder and can occur at all ages.

The most common cause of hypothyroidism results from an inflammation of the thyroid gland known as thyroiditis or Hashimoto's disease. It is an autoimmune disease that causes the immune system to try to destroy the thyroid gland. (An autoimmune disease occurs when the body's immune system becomes misdirected and attacks the very organs, cells, or tissues that it was designed to protect.) Another cause of hypothyroidism is not enough iodine in a person's diet. Iodine deficiency is rare in the United States, because many food products (such as table salt and bread) are supplemented with iodine. Iodine is found naturally in spinach, shrimp, oysters, and lobster.

Other common causes of hypothyroidism include:

• thyroid surgery for a complete or partial removal of the thyroid gland
• treatment with radioactive iodine
• radiation therapy to treat cancer of the head and neck
• medications such as lithium or too high a dosage of antithyroid medication used to treat hyperthyroidism

Hypothyroidism causes the body's functions to slow down. Mood swings including depression and forgetfulness may occur. Other symptoms include fatigue and sluggishness, loss of energy, dry skin and hair, increased blood cholesterol levels, heavy periods, increased sensitivity to cold, hoarse voice, trouble swallowing, a puffy face, unexpected weight gain, and constipation.

The thyroid gland, which is usually hidden by the layers of muscle in the neck, can become enlarged and seen as a big bulge in the neck. This symptom of hypothyroidism is called a goiter.

Many people do not know that they have a problem. A person may feel a little run down or under the weather at first. The symptoms develop slowly over a period of weeks or months. The flu, inactivity, or stresses are often blamed for the early symptoms. As a result, people seek care for vague problems. These range from physical illness to mental health problems. Years may pass before an under active thyroid is properly diagnosed. The lower the thyroid hormone levels become, the longer they stay low, and the more severe the symptoms will be.

Diagnosis is made by blood tests to measure the thyroid-stimulating hormone (TSH) and thyroid hormone thyroxine. Low levels of thyroxine and high levels of TSH indicate an under-active thyroid. Untreated hypothyroidism can lead to an enlarged heart, an increased risk of heart disease, decreased sexual desire, and slowed mental functioning.

Treatment for an underactive thyroid is hormone replacement therapy. A synthetic hormone is taken by pill to maintain normal thyroid levels. In most cases, the symptoms disappear within a few months. People with hypothyroidism need to take medication and require medical monitoring for the rest of their lives.

Last Reviewed 2004

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.

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