Older men will be glad to learn that in the largest study to date, testosterone gel improved sexual function and mood in men 65 and up with low testosterone levels. Previous trials of testosterone in this age group had given inconsistent results.

Those men who used a gel containing testosterone saw their blood testosterone rise to that of a typical young man. They reported improvements in all aspects of sexual function — including sexual activity, sexual desire and the ability to get an erection. “The benefits were quite convincing for sexual function,” study co-author, Thomas Gill, said in a statement.

Testosterone improved men's impression that their sexual desire, walking ability, energy level and overall health were better.

As men age, their testosterone level tends to drop. This is thought to contribute to a decline in sexual function, mobility and energy. But in 2003 the Institute of Medicine reported that there was no clear evidence that added testosterone benefitted older men with low T.

That was the main impetus for undertaking this study, also known as the TTrials.

The study, which was actually a group of seven different coordinated trials, was conducted at 14 different centers across the country. In all, 790 men 65 and older whose testosterone was low, apparently only due to age, either applied a testosterone gel or a gel with no testosterone daily for one year. Men were evaluated at 3, 6, 9 and 12 months, with all results self-reported by questionnaire.

Aside from the sexual benefits, men also reported better mood and decreased severity of depressive symptoms. There was no increase seen in overall energy. Results on walking ability — how far a man could walk in six minutes — were mixed. Adverse effects were similar in men who received testosterone and those who received placebo, but the TTrials were too small to draw any valid conclusion about testosterone and adverse effects.

Gill, Professor of Medicine and Epidemiology at Yale Medical School, noted one overall benefit that had not been seen in previous studies. “We found that testosterone improved men's impression that their sexual desire, walking ability, energy level and overall health were better.”

And since you're only as sexy as you feel, that's important.

The TTrials also tested testosterone's effect on cognitive function, bone, cardiovascular and anemia. Those results have not yet been fully analyzed but will be forthcoming.

The study appears in the New England Journal of Medicine.