The "placebo effect" may play a part in the athletic performance-enhancing effects of growth hormone, particularly in men, new findings suggest.
"Athletes are doping with growth hormone to improve performance, despite any firm scientific evidence that it does so," Dr. Kenneth K. Ho said at the Endocrine Society's annual meeting in San Francisco.
Ho, of the Garvan Institute of Medical Research, Sydney, Australia and colleagues randomly assigned 64 young adult recreational athletes to get growth hormone or an inactive placebo, without the participants or researchers knowing which was which, for eight weeks.
"We found that athletes who believed that they were taking growth hormone actually felt that their performance had improved and actually demonstrated improvement in physical performance, even though they were taking a placebo," Ho reported.
In general, everyone showed a small improvement in performance after the study, usually about 1 to 2 percent, he said.
"This is a well recognized training effect. But among those who wrongly thought they received growth hormone, the performance enhancement was about twice that — between 3 percent and 5 percent," Ho noted. "This phenomenon was far greater in men than in women."
"It is clear from our study that the mind plays amazing tricks on the body and this placebo effect has been known for many centuries. To our knowledge, this is the first study of the examination of a placebo effect in a sporting arena," Ho added.
The study was funded by the World Anti-Doping Agency and the Australian Government Anti-Doping Research Program.