MONDAY, March 17 (HealthDay News) -- In addition to ruining promising sports careers, human growth hormone may not even enhance athletic performance as it is purported to do.

An analysis of existing literature on human growth hormone found that while lean body mass increased, exercise capacity did not.

The findings add an ironic twist to the current controversy surrounding baseball greats Roger Clemens, Andy Pettitte and others.

Clemens has denied under oath using steroids and growth hormone, while Pettitte has admitted using human growth hormone to recover from injuries.

Last December, former U.S. Senate Majority Leader George Mitchell released a report affirming widespread use of performance-enhancing drugs in baseball.

"Our findings are consistent with the Mitchell report," said Dr. Hau Liu, lead author of the new analysis, which will be published in the March 17 online issue of the Annals of Internal Medicine.

The authors, however, warned of the difficulties of comparing use of growth hormone in a controlled study and use in the "real world."

In that so-called real world, dosages of growth hormone are probably higher, and the substance is often also taken in combination with other compounds, a practice called "stacking."

"This is not the final word," said Liu, an affiliated clinical assistant professor of medicine at Stanford University School of Medicine and associate chief of endocrinology at Santa Clara Valley Medical Center in San Jose. "This is basically a call for more research."

"Some people might use [growth hormone] by itself, and those may be looking more at the anti-aging benefit as opposed to performance enhancement," added Dr. Todd Schlifstein, an assistant professor of rehabilitation medicine at New York University School of Medicine in New York City. Many people take steroids along with growth hormone to maintain the benefit of the hormone, he said.

Liu's group had previously found that growth hormone had no effect on aging in healthy older people. "We said that we couldn't recommend its use for anti-aging purposes based on current evidence, because the risks outweigh the benefits," Liu said.

That done, the researchers decided to weigh the evidence on growth hormone and athletic performance. "Other authors have questioned whether growth hormone improves athletic performance," Liu said.

This meta-analysis looked at 44 existing articles from 27 different study samples which included individuals aged 13 to 45. All were randomized, controlled trials, considered the highest level of evidence in medical science.

Taking human growth hormone resulted in an average increase of 2 kilograms in lean body mass, which could include muscle, but also water (growth hormone promotes water retention). This was considered statistically significant.

There was also a "borderline" significant increase in fat mass of about 1 kilogram.

There was, however, no improvement in aerobic endurance. "If anything, we found a hint of evidence that it actually may worsen your performance," Liu said.

Nor did people taking growth hormone increase their ability to lift things.

Two of three articles showed increased lactate levels, a factor which can actually hurt athletic performance.

And there were unwanted side effects.

"They're using small doses, and even then, there were adverse effects," said Mary Chavez, chairwoman and a professor of pharmacy practice at the Irma Lerma Rangel College of Pharmacy at Texas A&M Health Science Center, in Kingsville. "We need to be cautious, because even here, some of these people are getting into muscle tears and edema and fatigue. Nationally, there is a bill before Congress to make it a controlled substance, not just prescription-only."

Last December, a bill to make human growth hormone a controlled substance was submitted in both the Senate and the House; it is currently moving through the committee process.

More information

The Nemours Foundation has more on growth hormone in young people.

SOURCES: Hau Liu, M.D., affiliated clinical assistant professor, medicine, Stanford University School of Medicine, and associate chief, endocrinology, Santa Clara Valley Medical Center, San Jose; Todd Schlifstein, M.D., assistant professor, rehabilitation medicine, New York University School of Medicine, New York City; Mary Chavez, Pharm.D., chairwoman and professor, pharmacy practice, Texas A&M Health Science Center, Irma Lerma Rangel College of Pharmacy, Kingsville; March 17, 2008, Annals of Internal Medicine, online

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