With the U.S. market for testosterone replacement therapy at nearly $2 billion (thanks largely to Androgel® sales) and as many as 13.8 million men older than 45 in the U.S. suffering from low levels of testosterone, it’s no wonder that the amount of research on testosterone and the male libido has ramped up in recent years.
The newest study, reported in the New England Journal of Medicine, suggests that estrogen might play a larger role in male libido than previously thought. The study found that lowering estrogen, the main sex hormone in women, in men undergoing low testosterone treatment resulted in drops in libido and an increase in body fat while testosterone levels improved.
The study followed 400 healthy men between the ages of 20 and 50 who had normal testosterone levels who received monthly injections of a drug that shuts off testosterone production in the testes. The men were then divided into five groups, with one administering a daily dose of a placebo gel and the other four applying varying doses of a testosterone gel daily. At the same time, half of the men received a medication that blocks the conversion of testosterone to estrogen.
The researchers watched the men over a 16-week period in which the study participants answered questions about their physical function, health status, and sexual function, among other tests like CT scans and leg strength exercises.
One thing became clear among the study’s participants: Sexual function was dependent on both testosterone and estrogen, as it declined in men deprived of testosterone, but even more so in men deprived of both of the hormones.
Currently, researchers don’t fully understand the role of estrogen in male sexual desire. That being said, the study’s researchers were surprised by the findings, because the common believe is that testosterone causes men to have stronger sex drives than their counterparts, according to Joel Finkelstein, one of the study’s authors and an endocrinologist at Massachusetts General Hospital.
“What will surprise many people is that loss of sexual desire in men with low testosterone is due to lack of estrogen,” Finkelstein said. “People think estrogen in men makes them very effeminate; they think of it as a female hormone, they think it is testosterone that gives men their sexual desire.”
In men, the body naturally converts a certain amount of testosterone into estrogen, and as the body’s levels of testosterone decrease, so, too, do estrogen levels. According to Finkelstein, the study’s findings shouldn’t change how individuals are treated for low testosterone. However, it should discourage drugmakers from developing new forms of testosterone replacement therapies that can’t be converted into estrogen.
Studies of this kind are likely to become more abundant in coming years so scientists and researchers can better understand the impact of hormone replacement therapies (HRT) on the body, from side effects to interactions with other drugs and genetics.
Has your doctor pointed out concerns over your estrogen and testosterone levels? We’d love to hear more about your experiences with HRT!