Q: The Major League Baseball scandal convinced me that it's illegal for baseball players to use human growth hormone. Yet some people say it's the fountain of youth. Is there a safe, legal way for me to take it?

A: Human growth hormone (HGH) has several legitimate medical uses, but "fountain of youth" is not among them. Physicians use it to treat children with dwarfism or with Turner's syndrome, a genetic disorder affecting girls. They have also had some experimental success with HGH in treating badly burned children, AIDS patients with excessive abdominal fat and frail, elderly patients. However, it is neither legal nor advisable to take HGH to look better or feel younger. There's a huge black market in HGH. Pro athletes grab the headlines, but they aren't the only customers. Wealthy adults trying to beat father time pay big bucks, too. The hormone has been sold as an antiaging remedy since the early 1990s, after a study published in The New England Journal of Medicine showed that it partially reverses the loss of muscle and gain of body fat that often accompanies aging. Young people taking HGH with anabolic steroids to improve their body's appearance have boosted its popularity, too. Some athletes say they take it to recover faster from injury.

HGH is a hormone made by the pituitary gland, the "master" gland that's located at the base of the brain (see illustration). As its name suggests, HGH plays a role in determining height. The pituitary releases small amounts of HGH until puberty. When the adolescent growth spurt ends, HGH levels steadily decline.

Human cadavers used to be the only source of HGH. That changed in the 1980s, when recombinant genetic techniques made it possible to splice the genes that churn out the hormone. Even with recombinant technology, it's expensive. Treatments run at least $1,000 a month. Some Internet vendors might offer cheaper prices, but these sources of HGH are highly unsafe: No one oversees what they put into a syringe. And because the body breaks down HGH during digestion, it must be injected. Not exactly convenient. Factors other than age influence HGH levels. One of the largest natural bursts of HGH comes within an hour of falling into a deep sleep. Diet can make a difference, too. High-protein meals stimulate HGH secretion, while high-carbohydrate foods -- and the resulting high blood sugar levels -- suppress it.

You can also pump up HGH secretion with exercise. Blood HGH levels can increase tenfold during a long session of moderate exercise. But some research suggests workout intensity affects HGH levels more than the time spent exercising. Age blunts the exercise response, so as you get older, the same workout produces a smaller spike in HGH.

Although the original study on HGH spawned many questionable enterprises, it has led to some interesting research. A series of experiments by researchers at Washington University in St. Louis showed that HGH makes people's muscles bigger but not necessarily stronger. Researchers hypothesize that's because HGH causes fluid retention and adds connective tissue but doesn't bulk up the contractile tissue that adds strength. It's also possible that these studies were too short and had too few participants to show a more subtle long-term effect. Keep in mind that these controlled experiments bear little resemblance to how elite athletes -- or even people at the local gym who want to look better -- actually use HGH. In a lab, researchers target patients' HGH levels to match those of healthy young adults. But at a gym, doses can surpass those levels many times over. Also, many people "stack" anabolic steroids on top of HGH or combine it with endurance-enhancing erythropoietin, the hormone that stimulates red blood cell production.

Scientific studies of HGH have been too small to pinpoint all the ill effects of prolonged use. Short-term studies have identified side effects such as soft-tissue swelling, joint pain, carpal tunnel syndrome and increases in blood sugar levels. For long-term effects, inferences have been drawn from patients whose pituitary glands secrete too much growth hormone, a condition called acromegaly. Acromegaly causes problems ranging from diabetes to high blood pressure to arthritis. It can make the bones in the skull and the jaw thicken and protrude. Researchers haven't proven that HGH causes cancer, but scattered evidence hints at a link.

Still tempted to try HGH? Well, ask yourself if it's really worth the risk and the cost. That money could be spent on nutritious food and strength training with a personal trainer, two things that are guaranteed to help you look and feel better -- safely.

<em>Submit questions to <a href="mailto:harvard_adviser@hms.harvard.edu">harvard_adviser@hms.harvard.edu</a>. Visit the Web site at <a href="http://www.health.harvard.edu/Harvard_Adviser.html" target="_blank">www.health.harvard.edu/adviser</a>.</em>