Waning energy, irritability, dry skin, a few extra pounds—could be you're spending too much time at work, or not enough time at the gym. But sometimes such vague and all-too-common symptoms can signal a larger problem.

Hypothyroidism—defined as underactive thyroid or the underproduction of thyroid hormones—is estimated to affect 11 million Americans, 9 million of whom are women. And since the thyroid gland is responsible for regulating many functions in the body, including metabolism, it makes sense that the underproduction of thyroid hormones would lead to a host of symptoms ranging from weight gain and fatigue to high cholesterol levels and possibly even infertility. Treating the condition can be simple: A daily dose of thyroid medication can effectively alleviate the problem. However, some experts believe certain foods such as soy may interfere with absorption of the medication, thus requiring that treatment be monitored. And because symptoms mimic those of general malaise and fatigue, the tricky part is establishing that you do in fact suffer from an underactive thyroid in the first place.

Thyroid Basics
The thyroid, a small gland shaped like the outspread wings of a bat, sits at the base of the throat, where it excretes hormones, mainly thyroxine, known as T4, and triiodothyronine, known as T3. The foremost job of these hormones is to help cells convert calories and oxygen into energy. This process can be interrupted by a variety of factors, including treatment for other thyroid conditions, iodine deficiency, pregnancy, and congenital abnormalities, but most often hypothyroidism is due to an autoimmune condition known as Hashimoto's thyroiditis, in which antibodies attack the thyroid and render it inactive.

"Women are much more prone to autoimmune diseases, which is one of the reasons why we see more hypothyroidism in women," says M. Sara Rosenthal, author of numerous books on thyroid health, including The Hypothyroid Sourcebook (McGraw Hill, 2002). Pregnancy, menopause and a greater life expectancy also contribute to the higher rate of this condition in women.

"There also seems to be a relationship between progesterone deficiency and hypothyroidism," Rosenthal says. When progesterone receptors malfunction due to factors such as stress or low blood sugar, she says, the thyroid also malfunctions. "When you recognize that progesterone is actually responsible for regulating thyroid hormone, it makes sense that low progesterone would mean low thyroid [activity]." A woman's best clue to whether she is deficient in progesterone is whether she suffers severe PMS symptoms. Therefore, women who do suffer from PMS should do some investigative work and have their thyroid checked, Rosenthal suggests.

"Frankly, I believe everyone should have their thyroid tested yearly," recommends Rosenthal. "The test is cheap, and oftentimes the condition will go undiagnosed for years otherwise."

But not everyone agrees that across-the-board routine testing is necessary. The American Thyroid Association promotes screening only for those 35 and older, while the American College of Physicians/American Society of Internal Medicine advocates screening for women age 50 and up. "I personally don't think people need routine checking," says Beth Burch, ND, of the Transitions for Health Women's Institute in Portland, Ore. "A good assessment of a patient's medical and family history along with a thorough physical exam should reveal whether or not a person is symptomatic and needs testing."

Like many holistic practitioners, Burch will first ask a potential hypothyroid patient to keep track of his or her basal body temperature for a few days to see if it is running low. If it measures less than 97.6 degrees several mornings in a row, she will prescribe tests to check for thyroid imbalance, including a TSH test, which measures the levels of thyroid-stimulating hormones in the blood. Generally, a normal reading is considered to be from 0.5­5, while anything greater than 5 suggests that thyroid hormone production is low. However, this measure is by no means the last word in diagnosing the condition.

"There are certainly people who feel their thyroid is functioning well [even though their test] numbers do not fall within the normal range, and there are those who test normal but who are suffering from hypothyroidism," says Rosenthal. Since these lab tests are not an exact science, it is always best to ask for further testing if you are not satisfied with the results. The British Medical Journal recently acknowledged that TSH test results can be ambiguous (2000, vol. 320, no. 7245, p. 1332), and suggested that the best way to determine who should receive thyroid treatment is not by a number, but by how a patient feels.

"You are the expert on your own body," Rosenthal says. "Even if your lab readings and your doctor are telling you that you are fine, you may be helped by hormone replacement."

To Treat Or Not To Treat
Thyroid dysfunction generally worsens over time. That means that early treatment can prevent more serious health problems down the line. A few well-controlled clinical trials have confirmed this, showing that even individuals suffering from the milder version of hypothyroidism—termed "subclinical hypothyroidism"—benefit from treatment (Journal of Clinical Endocrinology and Metabolism, 2001, vol. 86, no. 10, p. 4860).

Most conventional practitioners treat hypothyroidism with a daily dose of synthetic T4 (levothyroxine). T4 is typically prescribed alone because, in theory, the body will produce T3 from T4. The amount of supplementation will vary depending on the degree of hormone production in the body.

"The key is to start people slow and build them up," says Burch. "Doses must be monitored and tweaked, especially because rarely, but occasionally, people do resume thyroid hormone production."

Rosenthal, who has been using synthetic T4 thyroid since 1983, when she had her thyroid removed due to cancer, notes that treatment doesn't mean pharmaceutical dependence. "It is not a drug," she says. "It is a replacement hormone exactly identical to what your body normally produces."

Testing in the "normal" range doesn't always mean you don't need treatment. Trust what your body is telling you. Burch, contrary to standard practice, generally prescribes her patients natural Armour dessicated thyroid sourced from the glands of pigs because it contains both T4 and T3. According to Burch, some patients don't easily convert T4 to T3, and Armour relieves symptoms more effectively than the commonly prescribed synthetic T4. "Oftentimes when patients just take T4, their blood levels of thyroid normalize, but they are still symptomatic," says Burch. "But certainly one needs to use T3 very cautiously, because it is very potent."

Recent research backs up Burch's position, suggesting that some individuals may benefit from adding synthetic T3 to their medication regimen (New England Journal of Medicine, 1999, vol. 340, no. 6, p. 469). But Rosenthal urges caution. "I have looked at the studies and I don't think T3 should be viewed as a cure-all," she says. The problem, Rosenthal warns, is that the potent T3 can push some patients into a hyperthyroid state, producing its own set of debilitating symptoms (see "Is Your Thyroid in Working Order?"). She adds that, if monitored closely, the T3 hormone may help some people feel better.

"The bottom line is, you need to find the treatment that is right for you, because there is not a blanket medication recipe for everyone," she says.

Linda Knittel is a freelance writer specializing in health, nutrition and fitness.