March 18, 2008 -- Athletes who risk their careers and reputations by taking human growth hormones may be getting little in return, a new research review suggests.
Combined results from 27 studies did not support the claim that taking human growth hormones boosts athletic performance.
Short-term use of growth hormones was associated with increases in lean body mass, but not improvements in strength.
The studies were small and of short duration, with the longest lasting just 84 days.
Larger, longer studies are needed to conclusively determine whether growth hormone improves athletic performance, and if so, at what cost, researcher Hau Liu, MD, MPH, tells WebMD.
"Based on the current literature, we found no evidence that human growth hormones improved exercise capacity or athletic performance," he says.
Human Growth Hormone Studies
Human growth hormone is produced naturally in the body, and is essential for growth and development. A synthetic version, available since 1985, is used to treat growth hormone deficiency and other medical conditions.
Athletes take it in the belief that growth hormones will improve their performance and help them recover more quickly from injury.
But they are acting on faith, because the research doesn't prove these claims, Liu says.
The studies reviewed by Liu and colleagues from California’s Santa Clara Valley Medical Center and Stanford University included 303 physically fit healthy people -- mostly young men -- given growth hormone treatment either by injection or infusion.
The participants were followed for one month to just under three months to determine if the growth hormone affected body composition, strength, metabolism, and exercise capacity.
Although growth hormone use did seem to lead to increases in lean body mass, it did not appear to improve muscle strength.
And Liu says two of three studies examining exercise performance showed growth-hormone-treated patients had higher lactate levels than untreated control subjects, which could be indicative of diminished exercise capacity. Growth-hormone-treated participants also reported more fatigue.
The study appears in the May 20 issue of the Annals of Internal Medicine, but it was released online today.
"More research, including identification and evaluation of the real-world growth hormone doping protocols, is warranted to definitively determine the effects of growth hormone on athletic performance," they write.
Spotlight on Performance-Enhancing Drugs
Like anabolic steroids, growth hormone is banned by the World- and U.S. Anti-Doping Agency, the Olympic Committee, and most major and amateur sports leagues.
While steroid use can be detected though a simple urine test, this is not the case with growth hormones.
As a result, it is not at all clear how widespread growth hormone use is among student and professional athletes.
"The estimates have been from just about everyone to almost nobody," U.S. Anti-Doping Agency senior managing director Larry Bowers, PhD, tells WebMD. "We just don't know."
The recent release of the Mitchell Report examining performance-enhancing drug use in major league baseball helped shed some light on the issue.
Many of the players named in the report were accused of using steroids and human growth hormones.
The report concluded that there is little scientific evidence linking growth hormone to improved strength in athletes. It also questions the long-term safety of growth hormone use in healthy, fit people.
"As is the case with steroids, human growth hormone is associated with potentially severe adverse effects," the Mitchell Report noted.
In children and adolescents who are still growing, too much growth hormone can lead to a rare condition called acromegaly, characterized by exaggerated bone growth.
"Athletes who take growth hormones are really rolling the dice," Bowers says. "From my perspective, it is better to err on the side of caution if you don't know what the long-term risks are."