Thyroid: When the Body's Regulator Goes Wrong

Have you ever heard someone say, "I must have an overactive thyroid," to explain how they keep their weight down despite a hearty appetite? Or, conversely, hearing an overweight or obese person blame their girth on an underactive thyroid?

Although the thyroid gland does regulate the rate at which food is converted into energy, it may not necessarily explain your body's shape and silhouette. Your weight can be influenced by your diet, activity level, genetics and other factors. But the thyroid gland, located in the front of the neck, is extremely important to your overall well-being. It makes and stores hormones that also help regulate heart rate, blood pressure and body temperature. It's about the size of a quarter and shaped like a butterfly or bow tie.

"It's a fascinating gland," says Gilbert Fareau, MD, Medical College of Wisconsin Assistant Professor of Endocrinology, Metabolism and Clinical Nutrition. (Endocrinology involves the study of glands, hormones and their disorders.) "One of my patients described it as 'the body's furnace.' I like that definition."

Occasionally the thyroid stops functioning properly. It can become overactive, producing too much thyroid hormone (a condition called hyperthyroidism) or underactive, producing too little hormone (called hypothyroidism). Both hypothyroidism and hyperthyroidism can be treated effectively, Dr. Fareau says.

At the Froedtert & Medical College Endocrinology, Metabolism and Clinical Nutrition Clinic where Dr. Fareau practices, he estimates he sees more patients with hypothyroid conditions than those with hyperthyroidism.

Underactive Thyroid
"Hypothyroidism affects an estimated 4% to 8% of the population," he says, adding: "It affects 5 to 10 times as many women as men, often in their mid-50s." Why more women? "Hypothyroidism is usually due to an autoimmune disorder in which the body attacks its own cells or tissues. Autoimmune conditions, like lupus or rheumatoid arthritis, are frequently more common in women."

Hypothyroidism can occur gradually or suddenly, and its symptoms can be confused with other medical problems. Some symptoms of hypothyroidism are:

• Unexplained weight gain
• Constipation
• Cold intolerance
• Dry skin
• Fatigue
• Menstrual irregularities
• Joint pain
• A mass in the neck, also called a goiter
• A change in the voice

The most common hypothyroid condition is Hashimoto's disease, which may include the above symptoms - or no symptoms at all. In recent years, Dr. Fareau says, it's not unusual for patients with symptoms to suspect a thyroid condition after doing Internet research. "They'll say, 'I just don't feel right,' and list their symptoms. The diagnosis is confirmed by measuring their levels of TSH (thyroid stimulating hormone, which is produced in the brain) to find out if they are in the normal range. If those levels are low, we check for the antibodies associated with Hashimoto's. If it's appropriate, we begin hormone-replacement therapy."

The dose of hormone prescribed is estimated based on the patient's weight and other factors. Patients typically take a small pill every day, 30 minutes before or after a meal. Dr. Fareau says they usually check the hormone level six to eight weeks after starting the pill, and adjust the patient's dose as needed. Further follow-up can vary, but once an appropriate dose is achieved the hormone level stabilizes and only needs to be checked periodically (as infrequently as every six months to one year).

Overactive Thyroid
Graves' disease is the most common hyperthyroid condition. Some of its symptoms can be the reverse of those found in Hashimoto's. Graves' disease patients may experience: