As men age, their testosterone levels decrease, but prior studies of the effects of administering supplements of the hormone to older men have been inconclusive. Now, researchers at University of California, San Diego School of Medicine and 12 other medical centers in the United States have shown that testosterone treatment for men over the age of 65 improves sexual function, walking ability and mood.

The findings are published in the February issue of the New England Journal of Medicine.

Researchers across the nation have partnered with the National Institute on Aging to conduct the Testosterone Trials (TTrials), a coordinated group of seven studies to analyze the hormone. The first three studies that were conducted focused on sexual function, physical function and vitality.

“Low testosterone levels can result in excessive fatigue, weakness, depression and the loss of sexual drive in men over 65,” said Elizabeth Barrett-Connor, MD, study lead at the UC San Diego School of Medicine trial site and Distinguished Professor in the Department of Family Medicine and Public Health. “The results of the TTrials show for the first time that testosterone treatment of older men who have unequivocally low testosterone levels does have some benefit, including improved walking ability, sexual function and mood, with a decrease in depressive symptoms.”

The TTrials were led by researchers at the Perelman School of Medicine at University of Pennsylvania. Nearly 800 men enrolled in the study were randomized into two groups: one taking a daily testosterone gel for a year and the other a daily placebo gel. Efficacy was evaluated at months three, six, nine and 12.

In 2003, the Institute of Medicine reported that there was insufficient evidence to support any beneficial effect of testosterone in men age 65 and older. This report was the driving force for the TTrials, which are now the largest trials in the nation to examine the efficacy of testosterone treatment in older men whose levels are low, based on age alone.

Barrett-Connor adds that decisions about testosterone treatment for these men will also depend on the results from the remaining four studies in the TTrials, which include cognitive function, bone density, cardiovascular and anemia and have not yet been conducted.

The 13 medical centers involved in the TTrials are: UC San Diego School of Medicine, Perelman School of Medicine at  University of Pennsylvania, Albert Einstein College of Medicine, Baylor College of Medicine, Brigham and Women’s Hospital, Harbor-UCLA Medical Center, University of Alabama at Birmingham, Northwestern University Feinberg School of Medicine, Puget Sound Health Care System, University of Florida School of Medicine, University of Minnesota School of Medicine, University of Pittsburgh School of Public Health and Yale School of Medicine.

The TTrials were supported, in part, by a grant from the National Institutes of Health (NIH) (U01 AG030644). They were also supported by funds from the National Heart, Lung and Blood Institute, National Institute of Neurological Diseases and Stroke and National Institute of Child Health and Human Development.

Full study: www.nejm.org/doi/full/10.1056/NEJMoa1506119