A study published in the April 2004 issue of the journal Biology of Reproduction, found that a byproduct created in the intestine when the soy isoflavone daidzein is digested has an antiandrogen effect that could stop the progression of male and female pattern baldness and prostate cancer. The compound, known as equol, works by blocking the androgenic hormone dihydrotestosterone (DHT), known to stimulate prostate growth and scalp hair loss.
The researchers administered equol to rats for four to seven days and found a decrease in weight of two areas of the prostate. In a second experiment, equol was given to rats whose testes had been removed, rendering them unable to produce dihydrotestosterone. Injections of DHT stimulated prostate growth, but simultaneous treatment with equol prevented this from occurring. Equol did not influence hormone levels, but prevented DHT from functioning as it normally would by binding to the androgen receptor. Testosterone, estrogen, and dehydroepiandrosterone (DHEA) were not influenced by equol.
Over the past decade, pharmaceutical agents that inhibit the conversion of testosterone to dihydrotestosterone have been developed, but these drugs have side effects. Equol's mechanism of action is different, because if works by preventing the functioning of DHT rather than by blocking its formation. Senior author Robert J. Handa, PhD, of Colorado State University's College of Veterinary Medicine, explained, "Directly binding and inactivating DHT without influencing testosterone gives equol the ability to reduce many of the harmful effects of androgens without affecting the beneficial ones."
"This molecule is remarkable, stated study coauthor Kenneth Setchell, PhD, of Cincinnati Children's Hospital Medical Center, who first identified equol in humans. He added, "These findings are of immense clinical importance because blocking the action of the potent androgen DHT has been one of the holy grails of the pharmaceutical industry as a strategy for treating prostate cancer and androgenetic hair loss in women and men. This natural metabolite made from soy isoflavones, which are found in high amounts in soybeans, does this very effectively."