A new study in older men, published online November 20 in the Journal of Clinical Endocrinology & Metabolism, has shown that those with testosterone levels in the mid-range had the lowest rates of death from any cause.

This U-shaped association of testosterone with mortality differs from that seen in prior research, said lead author Bu Beng Yeap MBBS, FRACP, PhD, from the University of Western Australia, Perth.

"There was no benefit of having a high-normal testosterone level. Therefore, an optimal rather than a high testosterone level predicts [best] survival," Dr. Yeap told Medscape Medical News.

Trying to untangle all of this information on testosterone and its metabolites is difficult because different studies have provided conflicting results, particularly with regard to testosterone replacement therapy, Dr. Yeap conceded. While some research has suggested lower mortality in men treated with testosterone as opposed to controls, others have found the opposite.