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What You Should Know About Thyroid Testing

An important gland located in your neck just below the Adam's apple, the thyroid produces a hormone affecting many bodily functions, including heart rate, respiration, the central nervous system, and the reproductive system. This hormone also helps control the metabolic rate of the body—that is, the rate at which the body burns energy. So if the thyroid isn't functioning normally, a lot can go wrong. There are two main abnormalities, with generally opposite symptoms:

Hypothyroidism (underactive thyroid): With too little hormone, you may experience fatigue, weight gain, memory and hair loss, depression, difficulty sleeping and swallowing, mood swings, enlarged thyroid gland (also known as goiter), dry skin, intolerance to cold, and/or high cholesterol levels.

Hyperthyroidism (overactive thyroid, including Graves' disease): With too much hormone, you may experience irritability, nervousness, muscle weakness, tremors, irregular menstrual periods, weight loss, sleep disturbances, goiter, vision problems, palpitations, heat intolerance, and/or impaired fertility.

Women are at much higher risk than men for thyroid disorders. Hypothyroidism is more common than hyperthyroidism, especially among older women. It's estimated that up to 12% of Americans have thyroid disorders, according to a recent study of nearly 26,000 people from Colorado. The risk increases with age: about 6% of 40-year-old women have hypothyroidism, for instance, but 21% of those over 75. More than half of all cases have not been diagnosed. Hypothyroidism is treated with oral doses of synthetic or natural hormone.

Unlike most other chronic diseases, thyroid problems are not caused by diet, lack of exercise, smoking, or other factors you can change. Thyroid disease caused by iodine deficiency, which was common a century ago, is no longer a significant problem, since iodine is now widely dispersed in the American food supply.

Too much treatment—or not enough?

There is a reliable, inexpensive blood test to screen for thyroid disease—the TSH (thyroid stimulating hormone) test. However, it may be hard for a doctor to spot a thyroid disorder, particularly if the malfunction is minor ("subclinical"), in which case the symptoms are usually mild or nonexistent. Moreover, most of the symptoms are not unique to thyroid disease. Hair loss and sleeplessness, for instance, are common in older people who are perfectly healthy and have no thyroid problems. Many symptoms of menopause are the same as those of thyroid disorders. Feeling tired all the time and gaining weight are widespread complaints these days—an underactive thyroid is not usually to blame.

Beginning around 1960 many doctors readily prescribed thyroid hormones for such general symptoms, often without measuring hormone levels. But thyroid hormones have no benefits unless you really are deficient. And since they can have serious side effects, such as bone loss, you don't want to take them unless you really need them.

The cholesterol/thyroid connection

Lack of thyroid hormone decreases the liver's ability to clear cholesterol from the blood: thus, people with hypothyroidism tend to have elevated blood levels of total cholesterol, LDL ("bad") cholesterol, and triglycerides. Moreover, a large Dutch study of women over age 55, published this February, found that those with low levels of thyroid hormone (11% of the group) had about double the risk of atherosclerosis and heart attack.

If you have high blood cholesterol, your doctor should check to see if an underactive thyroid is responsible, especially if you are an older woman. If so, it makes more sense to treat the thyroid condition first than to try to lower cholesterol via diet or medication, which then may have little effect. Treating the thyroid problem typically results in a 20 to 30% reduction in cholesterol. If cholesterol levels remain high, other treatments can be tried.

Who should be tested?

Routine screening—that is, testing all people, even if they have no symptoms or risk factors—for thyroid problems remains controversial. However, thyroid testing should certainly be done if

• You have a family history of thyroid problems, since there seems to be a genetic element.

• You have symptoms that may be related to a thyroid disorder.

• You have high cholesterol levels.

• You have had radiation to the neck, have diabetes or pernicious anemia, or have taken lithium for psychiatric disorders. If you fall into any of these categories, you are at high risk for thyroid problems.

Even if you don't fall into one of these categories, if you're a woman over 50 talk to your doctor about thyroid testing. Be sure to report any symptoms you have. According to the American Association of Clinical Endocrinologists, disorders of the thyroid are underdiagnosed in Americans, especially in older women, who are at greatest risk for thyroid disease. Some authorities recommend testing every five years.

If you do need thyroid hormones, you must be carefully monitored to make sure your dosage is correct. You may also need to take steps to reduce your risk of bone loss. The good news is that hypothyroidism responds very well to treatment.