Experts believe a new test to detect human growth hormone may bring sports authorities a step closer to catching doping athletes.
"This new test is more sensitive to human growth hormone than what we've had in the past," said Ho. "My message to athletes would be to train harder instead of cheating."
It has been notoriously difficult to identify athletes illegally using human growth hormone. Not only is the hormone naturally produced in the body — making it harder to detect synthetic versions — but the concentrations of it normally circulating in the body vary enormously and can disappear within minutes.
Human growth hormone is produced by the pituitary gland and helps cells regenerate. Synthetic versions of the hormone are routinely prescribed to children with growth problems, or tuberculosis and AIDS patients who need to maintain their body weight.
It is also widely taken among some anti-aging advocates since it can improve skin elasticity. But improper use of the hormone can lead to problems including the nerve disorder acute carpal tunnel syndrome, diabetes, and unnatural growth of the bones.
The new test works by finding proteins triggered by the hormone. "We've been able to identify markers that show abuse by measuring when other hormones and proteins released by human growth hormone reach certain levels," said Dr. Olivier Rabin, WADA's science director. Rabin said that these biological markers are not affected by any other differences between athletes, such as ethnicity, gender, or physiology.
WADA has already introduced another test, which identifies the synthetic version of human growth hormone in the body, on a limited scale. That test was in place at the Athens and Turin Olympic Games. The agency hopes to use both tests together to maximize their chances of detection. But finding cheating athletes on a large scale will be difficult since the hormone can only be detected in blood — only trace amounts are present in urine. And blood tests are not used as regularly as urine tests.
While designing the new test, Ho and his colleagues also made another interesting discovery: human growth hormone doesn't work on its own.
In their research, Ho and colleagues looked at the effects produced by human growth hormone on its own and in combination with testosterone, in nearly 100 recreational athletes.
In the study, 64 men were given either a placebo, human growth hormone, testosterone, or a combination of the latter two, for eight weeks. In the other half of the study, 33 women were given a placebo or the growth hormone, for eight weeks. Their physical performances were then tested in various categories, including how much weight they could lift, how high they could jump and how fast they could sprint.
"We found that growth hormone does not increase muscle mass or improve performance," Ho said. "Only when you combine growth hormone with testosterone does it have an effect," he said. When taken together, the two substances have a synergistic effect, lowering the body's fluid and fat levels while building muscle.
But the conclusions from Ho's study are limited. Ho acknowledged that while study participants were given "high but safe" doses of human growth hormone and testosterone, professional athletes that are doping would probably use much higher levels for longer periods.
While Ho and colleagues concluded that the differences between athletes on various treatment regimens were not statistically significant, some experts think the differences cannot be altogether dismissed.
"In the laboratory, very small differences may not be significant for scientists," said Dr. Charles Yesalis, professor emeritus of health and human development at Pennsylvania State University. "But we can't always measure small differences that are unbelievably important in sport." Yesalis was not connected to the study.
Experts also suspect that the vast majority of doping athletes already use a cocktail of banned substances. "Athletes taking human growth hormone probably take it in conjunction with a steroid," said Dr. Todd Schlifstein, a sports medicine rehabilitation physician at New York University Medical Center's Rusk Institute. Human growth hormone is thought to prolong the effects of banned substances.
And because there is not yet any widespread test for human growth hormone, athletes can continue taking it even when they are being drug-tested. "This is possibly a way for athletes to maintain the effects of steroids without taking the chance of getting caught," Schlifstein said.
With the new tests however, WADA hopes that will no longer be the case. Rabin said WADA is now working to make the human growth hormone tests more widely available, and expect them to soon make a dramatic impact on professional sports.
Others, like Yesalis, are not so sure. "We have heard for years that a reliable test is coming soon," he said. "When I see athletes getting smaller and no Olympic or world records being broken, that's when I'll believe it."