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When it comes to men's bodies, testosterone is a marker of youth. Levels of the sex hormone tend to peak during the teen years through early adulthood and then decline gradually as men age.

The consequences of this loss can be harsh: sleep disturbances, physical changes from increased body fat and reduced muscles to hair loss, reduced sexual desire. But while the idea of replacing testosterone with gel, patches and injections may sound tempting, there haven't been a lot of studies on the subject. Those that have been published have had mixed results, leave many physicians confused about the risks versus benefits of such therapy.

Now a study on 83,000 veterans provides some evidence that it can work. In a study published in the European Heart Journal, researchers found that patients with low testosterone levels who received testosterone replacement therapy (TRT) could be at lower risk for heart attack or stroke.

The study -- the largest to-date on TRT and with the longest followup period -- involved men who were treated between December 1999 and May 2014 at the Kansas City VA Medical Center. Only 63 percent of the men achieved normal testosterone levels with TRT, and that group had significant fewer deaths and cardiovascular events than the group that did not.

"This is the first study to demonstrate that significant benefit is observed only if the dose is adequate to normalize the testosterone levels," Rajat S. Barua, a cardiologist who is a co-author of the paper, said in a statement.

The researchers emphasized that their study does not draw any definitive conclusions about TRT and that further long-term followup is needed. Previous studies have shown that testosterone therapy can increase the risk of heart attack or stroke and has been linked to other scary effects such as causing faster-growing prostate cancers, blood clots and sleep apnea.

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