Last Updated: 2002-11-12 11:18:50 -0400 (Reuters Health)

By Jacqueline Stenson

NEW YORK (Reuters Health) - Growth hormone, widely touted as a restorer of youth for aging Americans, offers limited benefits to seniors and carries potentially serious risks, new study findings indicate.

Despite its growing popularity, growth hormone as an anti-aging strategy is "not yet ready for prime time," said study author Dr. S. Mitchell Harman, director of the Kronos Longevity Research Institute, an independent nonprofit group in Phoenix, Arizona.

"It's not a wonder drug, and it has real risks," he told Reuters Health.

Elderly men and women taking growth hormone gained some muscle and shed some fat over 6 months. But only those men taking both growth hormone and testosterone saw any functional gains in strength and cardiovascular endurance, and those gains were modest, Harman and colleagues at the National Institutes of Health and other centers report in the November 13th issue of The Journal of the American Medical Association.

And along with other side effects, the risk of diabetes and glucose intolerance, a precursor to diabetes, was heightened among men on growth hormone.

Hundreds of anti-aging clinics across the country already offer growth hormone injections, and health-food stores sell supplements claiming to contain the hormone, Harman said. While there are no statistics on how many Americans take growth hormone, the number is probably in the tens of thousands, he estimated.

The injections contain a synthetic version of human growth hormone, which is naturally produced by the pituitary gland in the brain and declines with age. The synthetic drug has been approved by the Food and Drug Administration for children with short stature resulting from very low human growth hormone levels. It also is used in adults with such conditions as severe growth hormone deficiency and muscle wasting associated with AIDS.

But whether growth hormone can help reverse the effects of normal aging is an ongoing debate.

The latest study involved 74 men and 57 women, all healthy seniors between 65 and 88 years of age. Participants were randomly assigned to one of four treatment groups: growth hormone plus sex steroid (testosterone for men; hormone replacement therapy for women); growth hormone plus placebo (inactive) sex steroid; placebo growth hormone plus sex steroid; or placebo growth hormone plus placebo sex steroid. All participants were instructed to maintain their current diet and exercise regimens.

By the end of the 26-week study, women on growth hormone had gained an average of 2 to 5 pounds of muscle and lost about 5 pounds of fat. Likewise, men on growth hormone had gained 7 to 10 pounds of muscle and shed about the same amount of fat.

Yet only one study group experienced actual functional improvement. "In men, the combination of growth hormone and testosterone showed small increases in endurance and strength," Harman said. As with growth hormone levels, testosterone levels also decline with age.

In this group of men, cardiovascular endurance increased 8%. Muscle strength increased 7%, though this latter finding was on the borderline of statistical significance.

Side effects from growth hormone were most common in men and included swelling of the arms and legs, carpal tunnel syndrome, joint pain and most worrisome, diabetes and glucose intolerance. Eighteen men taking growth hormone developed either diabetes or glucose intolerance during the study, compared with seven men not taking growth hormone.

And there could be other, unknown side effects as well, Harman said, noting that seniors are far more likely than children to develop adverse reactions from growth hormone.

"We don't know whether taking growth hormone long term will put you at higher risk for cancer but there's certainly reason to think it might," he said. Growth hormone raises blood levels of another hormone, insulin-like growth factor, which preliminary evidence indicates may promote breast and prostate cancers.

While the new findings suggest growth hormone may have some role in fighting aging, small improvements in strength or endurance are "not the same as being able to carry two bags of groceries up a flight of stairs" or perform other important tasks of everyday living, Harman said.

More studies are needed to fully understand the effects of growth hormone in aging people, he said, and to determine whether different doses for longer time periods would yield more benefits--or risks.

SOURCE: The Journal of the American Medical Association 2002;288:2282-2292.