Of all the problems that can undermine good health and accelerate the aging process, none is more common--or more likely to be overlooked--than an underactive thyroid gland. Keeping your thyroid functioning properly is a powerful anti-aging strategy. And there is a simple test you can do to determine if your thyroid is low.

The chances are good that you have an underactive thyroid. Undiagnosed hypothyroidism is of epidemic proportions. Although 25-40 % of the population suffers from a low thyroid, very few are aware of it.

Here is a simple test you can do tonight to determine if your thyroid is low. Simply take your Basal Metabolic Temperature. This is the lowest temperature your body reaches, which occurs just before you get up in the morning. So before you go to bed, shake down an oral mercury thermometer (not a digital thermometer), and set it where you can reach it when you wake up. (Shaking it in the morning, or even getting up to go to the bathroom will affect the test.) Tomorrow morning, before you get out of bed, place the thermometer in your armpit and leave it there for ten minutes. Read it and then put it back for another two minutes. If you get the same reading (i.e., it has stopped going up), this is your Basal Metabolic Temperature (BMT). If your BMT is consistently below 97.8, you are hypothyroid.

The next step is to find a doctor who will treat you. This may prove difficult because mainstream doctors are programmed to look at laboratory tests rather than clinical symptoms and Basal Temperatures to make this diagnosis. The most common error is that the doctor will measure your TSH (Thyroid Stimulating Hormone) level and if it is not above 4.5, you will be told that your thyroid is okay. (The TSH goes up as the level of thyroid hormone goes down, so a higher level indicates a low thyroid.) The truth is that your TSH can be as low as 1.5, and if you have the symptoms of hypothyroidism and your BMTs are low, you almost certainly are hypothyroid. If this is the case, locate an alternative doctor who has experience treating 'subclinical (meaning it doesn't jump out at you, but it's there in the background causing health problems) hypothyroidism.'

One reason it is important to diagnose and treat subclinical hypothyroidism is that a low thyroid is very often the unsuspected underlying cause of other serious chronic health problems. These may include cardiovascular disease, immune disorders, nervous system diseases, skin afflictions, gynecological problems, or any other of a broad spectrum of diseases. When this is the case, treating the 'presenting problem' (the angina, allergies, depression, eczema, infertility, etc.) will not be effective unless the thyroid imbalance is corrected as well.

The single most common complaint in people with underactive thyroids is low energy. But since any organ or system can underfunction, symptoms range all over the map: dry skin, intolerance to heat or cold, depression, memory loss, easy fatigue, muscle weakness, infertility, PMS, sleep disturbances, loss of hair, dry skin, heart palpitations, circulatory problems, emotional instability, inability to lose weight, frequent infections, allergies, digestive problems, constipation, anemia, elevated cholesterol levels. No wonder doctors usually fail to suspect thyroid malfunction; they're dealing with an entity with many faces.

Your thyroid gland's function is important to your health because thyroid hormone produced by the gland travels to each cell of your body and determines that cell's rate of metabolism. In other words, it tells each of your 100 trillion cells how fast to work. If you produce too little of the hormone, your cells get sluggish. If the cell is a nerve cell, your thinking may slow down or depression may set in. If the cell is a muscle cell, your strength declines.

If the cell is an intestinal cell, your digestion may be affected. The colon may become sluggish, causing constipation. Food allergies or intestinal infection will be more likely.

If that thyroid deprived cell happens to be an immune cell, you may have allergies or more frequent infections. The immune system is especially vulnerable to low thyroid performance. White blood cell production may slow down and cells that fight infections may lose their aggressiveness.

If your Basal Metabolic Temperature is low, the next step is to ask your alternative doctor to order a `hypothyroid panel' and an `anti-thyroid antibody panel.' The TSH (thyroid stimulating hormone) level is especially important. If you have symptoms of hypothyroidism, your temperatures are low, and your TSH is above 2.0 (TSH goes up ad the thyroid hormone level goes down), you will probably need natural thyroid hormone replacement therapy (I usually use Armour thyroid.)

For more about the thyroid, and for information on how to proceed if yours is low, see Chapter 36 of Renewal: The Anti-Aging Revolution.