Hypothyroidism

Thyroid hormone keeps your body working at the right speed. If your thyroid hormone level drops, the cells throughout the rest of your body slow their activity (see Figure 2 below). As a result, many systems in your body slow down, creating a wide range of symptoms that may include fatigue, depression, weight gain, constipation, and dry skin, all of which can be misinterpreted as signs of other problems.

Figure 2: Hypothyroidism A normal thyroid gland (left) releases the correct amount of thyroid hormone (T4 and T3). If the thyroid gland fails to release the correct amount (right), changes in the hypothalamus and pituitary lead to increased TSH production in an effort to increase the thyroid's output. But the diseased thyroid gland continues to lag in production of thyroid hormone, causing the body's metabolism to slow down. Some portions of the damaged thyroid gland might enlarge, becoming goiter.

Because most people and their doctors do not connect these symptoms to thyroid disease, many people with hypothyroidism don't know they have it. In 2000, 26,000 visitors to a statewide fair in Colorado had their blood tested for thyroid hormone. Researchers found that almost 10% of these people had undetected hypothyroidism. The U.S. National Health and Nutrition Examination Survey (NHANES III) found that nearly 10 million people in the United States have hypothyroidism.

Hypothyroidism occurs in approximately one in eight women ages 35 to 65. After age 65, the incidence increases to one in five (see Figure 3 below). One study of women over 60 from several senior citizens' centers and ambulatory clinics found that as many as 24% were hypothyroid. Yet, in older people, the disease is probably recognized the least. That is because the symptoms are far more elusive in this age group.

Figure 3: Hypothyroidism by age After age 35, the percentage of people with hypothyroidism begins to increase, particularly among women. Reprinted with permission from Archives of Internal Medicine, Feb. 28, 2000.

People over 60 with thyroid disease are much less likely than younger people to experience classic multiple symptoms. They may have only one symptom. For instance, it is not unusual for an older person to experience only memory loss or only depression, either of which is easily attributed to normal aging or other problems. In older people who do experience the classic symptoms of weight gain and fatigue, these symptoms of hypothyroidism may be mistaken as typical signs of aging.

Only a special blood test can confirm whether you are hypothyroid, so it is important to be aware of the symptoms and ask your doctor for a thyroid evaluation if you are over 60, have symptoms, or have any risk factors (see "Risk factors for thyroid disease" above). Thyroid tests are not done routinely unless your doctor believes you are at risk or have symptoms. If left untreated, over time, hypothyroidism can have serious consequences. It increases your risk for high cholesterol, high blood pressure, atherosclerosis, and heart attack. In addition, a form of severe hypothyroidism called myxedema can develop over time, when the body slows to the point that it starts to shut down and may fall into a coma.

Once the diagnosis is made, hypothyroidism is very easily treated with levothyroxine sodium, a synthetic version of T4. With proper treatment and routine checkups, you can resume a normal life, usually free of symptoms.