DHEA is a precursor of other hormones, which means that upon arrival, it sets off a chain reaction that produces another kind of hormone. Once in the tissues, it is converted to the appropriate sex hormone for that tissue. For some tissues, the male hormone testosterone is required. Other tissues receive the principal female sex hormone, estrogen, and still others get both types of hormones.

When a woman gets DHEA, for example, it’s converted to estrogen in the ovaries. In a man, it’s converted to testosterone in the prostate. In both sexes, DHEA is transformed into testosterone and estrogen in the muscles. Add together these hormonal effects, and it becomes apparent why proponents are making so many claims for DHEA. This hormone supplement, they say, should stop or even reverse the aging process and the diseases that can occur in our later years.

There is a danger in taking DHEA supplements, though, because a number of tumors are hormone-dependent, says Richard L. Sprott, Ph.D., executive director of the Ellison Medical Foundation, an organization that funds research on the biology of aging, in Bethesda, Maryland.

If you have an existing hormone-dependent tumor such as a testicular or prostate tumor, DHEA could be sent directly to the tumor, where it would be converted into the testosterone that the tumor needs to grow. "The tumor will kill you sooner than it would have otherwise," Dr. Sprott explains. The same may be true for endometrial, ovarian, and breast tumors in women.

For elderly men, there could be a significant risk. Among men ages 70 to 74 in the United States, more than 1 in 100 will be diagnosed with prostate cancer each year. But that doesn’t mean that it’s the leading cause of death among this group. According to Dr. Sprott, "It’s a very slow-growing cancer that won’t kill them before they die of other causes. But if you were to feed DHEA to the tumor and accelerate its rate of growth, the cancer might become significant and life-threatening."

DHEA production peaks between the ages of 25 and 30, then declines with age. This decline is the reason that some suggest that aging may be linked to DHEA deficiency. Replenish DHEA, they argue, and you’ll slow the effects of aging. But diminishing DHEA levels could also mean that elderly people simply don’t need as much, says Dr. Sprott.

"Many things decline with advancing age," he adds. "Whether DHEA is important in that decline is unknown, although the dietary supplement industry suggests that it’s a causal relationship. We don’t know that it is. We’re not trying to say that DHEA has no effect, but we do think that there is significant risk that has not been explained to the consumer."

Taking these risks into account, researchers are still exploring the possible benefits of DHEA . As studies continue, doctors may find that DHEA, taken judiciously, has other promising uses. Dr. Sprott says that the most encouraging DHEA data he’s seen was a study of systemic lupus. In this type of lupus, the immune system seems to attack normally healthy cells and tissue. There are many long-lasting symptoms that involve the skin, joints, kidneys, and other tissues and organs.

In a study of women with mild to moderate systemic lupus, 14 received 200 milligrams of DHEA daily for three months, while a second group of 14 women received a look-alike pill (placebo) that contained no DHEA. At the end of the study, two-thirds of those receiving DHEA showed marked improvement. Women in the placebo group showed almost no improvement.

There is also preliminary evidence that DHEA may boost immunity, enhance memory, and improve mood, energy, and libido in the elderly. It may reduce the risk of type 2 (non-insulin-dependent) diabetes. One study even suggested that DHEA may have a future role as an adjunct to hormone replacement therapy, helping out the estrogen that’s a standard element in this treatment for postmenopausal women.

It’s important to note that much of the DHEA  research is based on animal data, says Arthur G. Schwartz, Ph.D., researcher and microbiologist at Temple University Medical School in Philadelphia, who has been studying DHEA for over 20 years.

Many supplement manufacturers are picking up on the results of animal studies and applying them to humans—an irresponsible practice, as Dr. Schwartz sees it. One of his studies reporting anti-obesity effects of DHEA on laboratory animals was widely touted by manufacturers as proof that DHEA could promote weight loss in humans, but it’s not true, he says.

Doses found in supplements are based on the doses given to animals in laboratory experiments—from 25 to 50 milligrams daily, says Dr. Schwartz. When you convert that amount to what a human would need to get the same or similar effects for weight loss, though, you’d have to increase the dose to up to 2,000 milligrams a day.

Working with the National Cancer Institute, Dr. Schwartz has also tested a modified compound of DHEA. It may have some of the positive benefits of DHEA, but at a lower dose and without producing the hormonal side effects. Even if the results continue to be promising and the DHEA passes tests for approval, however, don’t expect to find modified DHEA on store shelves, Dr. Schwartz says. For this form of DHEA, you will probably need a prescription.

Most people who take DHEA are overdosing, says Ray Sahelian, M.D., a physician in Marina del Rey, California, and author of DHEA: A Practical Guide. Although he’s a proponent of DHEA, he’s concerned that many people are taking doses of 25 milligrams or more daily, an amount that can lead to side effects he’s seen in his patients, including acne, growth of facial hair on women, irritability, accelerated scalp hair loss in both men and women, and even irregular heart rhythms. A less measurable effect may be the possibility of accelerating tumor growth, according to Dr. Sprott.

Dr. Sahelian says that he has lowered his recommended dose significantly, to 1 to 5 milligrams daily, since he first started prescribing DHEA to his patients. The problem is that many supplements are sold in 25-milligram or 50-milligram capsules.

Almost nothing is known about DHEA’s interactions with other drugs or its long-term effects. "This doesn’t work fast, like poison. You’re not going to take DHEA for a week, develop a testicular tumor, and die. This is something whose effects you might not see for 5 to 10 years. And by then, it’s too late, because you’ve been accumulating a risk over a long period of time," warns Dr. Sprott.

The Food and Drug Administration (FDA) banned over-the-counter sales of DHEA in 1985, but the ban was lifted with the passage of the Dietary Supplement Health and Education Act of 1994. This law allows certain substances to be sold for human consumption without FDA approval, as long as they are marketed as "dietary supplements" and not labeled for a particular use like prescription or over-the-counter drugs.

To make DHEA supplements, vitamin and pharmaceutical companies extract sterols, most commonly diosgenin, from wild yams. Some supplements, however, are extracts of wild yams that haven’t been processed into DHEA. These are marketed as containing natural precursors for the body’s production of DHEA , but they have not been found to boost DHEA levels.