Men lose testosterone as they age and this is believed to affect their sense of well-being and sexual function. In recent years, more than a million men smeared testosterone gels on their bodies in the hope that that this would rejuvenate them and boost their libido.

Findings of a landmark study, however, suggests that while the treatment provides modest improvement in men's walking strength, mood and sex lives, testosterone treatment is not a fountain of youth as the gains were observed to eventually wane.

For the new study published in The New England Journal of Medicine on Wednesday, Peter Snyder, from the University of Pennsylvania, and colleagues asked about 800 men to rub their skin with either a testosterone gel or a placebo for a year.

Those in the testosterone group experienced moderate improvements in sex lives but the benefits in erectile function were not comparable to those seen with Viagra. They also had slightly better improvements in mood and walking strength compared with those in placebo albeit the researchers found no difference in terms of energy boost.

"Testosterone treatment had a moderate, significant benefit with respect to sexual function but no significant benefit with respect to walking distance (among participants in the Physical Function Trial) or vitality," the researchers wrote in their study. "Testosterone treatment also had a significant benefit with respect to other prespecified outcomes, including walking distance when men in all three trials were included and mood and depressive symptoms."

The results of the study suggest the treatment is not the answer for age-related conditions. The findings likewise suggest albeit do not prove that the hormones increases energy and strength and builds muscles.

"The results show that testosterone therapy did yield certain benefits, but at this point their clinical importance is uncertain," commented Eric Orwoll, from the Bone Density Lab at Oregon Health and Science University in an accompanying editorial. "Therapy was not a panacea, and the findings alone might be insufficient to support a decision to initiate testosterone therapy in symptomatic older men."

Earlier research suggests that boosting testosterone levels may elevate risk for heart attack and stroke as well as prostate issue but the researchers said that they have not found an increase in adverse events among participants who took the hormone.