Treatment with testosterone improves sexual function and mood in older men with low testosterone levels, report Yale researchers. The results of the Testosterone Trials (TTrials), conducted at 12 sites nationwide, including Yale School of Medicine, were the first to convincingly show the benefits of testosterone for men over age 65, said the researchers.

The study, conducted in partnership with the National Institute on Aging, was published by the New England Journal of Medicine.

As men age, their testosterone levels tend to decline, leading to decreases in sexual function, mobility, and energy. While testosterone has been studied as a potential treatment, the results of previous trials have been inconsistent.

To test the potential benefit of testosterone treatment in men who had low testosterone levels for no other reason than advancing age, Yale researchers collaborated with investigators at 12 institutions, led by the University of Pennsylvania, to conduct the TTrials. Yale enrolled the largest number of participants at any one site (84 of 790) for these double-blind, placebo-controlled trials that investigated the efficacy of testosterone gel for multiple outcomes, including sexual function, physical function, and vitality.

The researchers found that men who received testosterone therapy for one year, versus those on placebo, saw significant improvements in sexual function, including sexual activity, sexual desire, and erectile function.

"There appears to be benefits for treatment with testosterone among men who have unequivocally low levels of testosterone that are attributable solely to age," said Thomas Gill, M.D., the Humana Foundation Professor of Medicine (Geriatrics) and a study co-author. "The benefits were quite convincing for sexual function."

While participants enrolled in the trial that assessed physical function did not see significant improvements in their walking ability -- as measured by an increase of 50 meters or more in their distance walked in 6 minutes -- an increase was found when all study participants were evaluated. In addition, men enrolled in the vitality trial saw modest benefits in terms of improved mood and fewer depressive symptoms.

While the results were somewhat mixed, Gill noted an overall benefit that had not been seen in previous studies. "One way of interpreting the results across trials is a global impression of change," he said. "We found that testosterone improved men's impression that their sexual desire, walking ability, energy level, and overall health were better."

Researchers also reported that there were no increases in adverse side effects a year after testosterone therapy was discontinued. However, a larger trial would be needed to conclusively demonstrate safety over time, the researchers said.