Human growth hormone has been thought of as a "fountain of youth" because it increases muscle mass and height and decreases the amount of fat tissue. The hormone has become popular with athletes, who use it in high doses to boost performance. HGH is not approved for use in this fashion.
Until 1990, the main reason someone took human growth hormone was to grow taller.
But a study published that year found raising HGH levels in healthy men ages 61 to 81 led to increased muscle mass and decreased fat tissue.
At extremely high doses -- those thought to be used by athletes -- HGH can cause major health problems and shorten life.
"Large doses of growth hormone are clearly toxic," said Dr. Mitchell Harman, director of Kronos Longevity Research Institute in Phoenix and a growth hormone researcher.
High doses of HGH can cause acromegaly, a disease characterized by enlarged hands, feet and foreheads, abnormal bone growth, arthritis and enlargement of the heart.
Dr. Robert Butler, president of the International Longevity Center in New York, said the study was well done but involved only 12 men over six months.
"Long-term use is another matter about which we don't know very much," he said.
Butler and others warn that doctors don't know enough about the possible dangerous side effects, such as diabetes and cancer.
Human growth hormone is not approved for anti-aging or athletic performance enhancement, but once a drug is approved for one use, doctors are allowed to prescribe it for any reason if they feel patients will benefit.
There may not be any true indications for it other than the aspiration to be a winner."
Dr. John Lacouture, a Charlotte internist who specializes in anti-aging medicine, said he has changed his mind about what he once thought were anti-aging benefits of HGH.
"It increases strength and energy and muscles.
But maintaining the level of growth factors throughout life at high-normal, I'm not sure that's a good strategy for successful aging.