The key new findings:
- Testosterone had no effect on memory or mental function, based on tests given before, halfway and at the end of treatment to nearly 500 men with age-related memory decline.
- Among almost 140 men who underwent heart artery imaging tests to see if the hormone slowed progression of plaque, those who used testosterone had more plaque buildup and narrower arteries after a year than the fake gel group. Those changes could signal increased chances for heart attacks although none occurred in the study. Men in this sub-study were already more vulnerable for heart problems because of conditions including artery disease, obesity and high blood pressure.
- Among about 200 men given bone imaging tests before and at the end of treatment, those on testosterone showed increases in bone density and strength, especially in the spine, while minimal changes were found in the group that used fake gel. The improvement was similar to bone changes seen with treatment for osteoporosis, although most men studied did not have that bone-thinning condition, which can lead to fractures.
- Among 126 men with anemia — a fatigue-linked condition involving inadequate red blood cells — those on testosterone showed substantial improvement. By the study's end, anemia had vanished in almost 60 percent of men on testosterone compared with 22 percent of the fake gel group. The hormone group also reported having more energy.
"The overall health benefits, however, remain to be determined," the researchers said.
The studies were published Tuesday in the Journal of the American Medical Association and JAMA Internal Medicine. AbbVie Pharmaceuticals provided its gel for the study and helped pay for the research but had no other role in the study.
The research was not designed to look at risks and does not apply to younger men or those with normal levels of testosterone, said study leader Dr. Peter Snyder, a University of Pennsylvania hormone specialist. It's also not known if other forms of testosterone supplements would have similar effects in older men with low levels.
Prescription testosterone products, including gel, are approved only for men with low levels of the hormones caused by various medical conditions. Benefits and risks are unknown in men whose levels are low due only to aging, the FDA says. The agency requires testosterone labels to include possible risks for heart attacks and strokes, based on some previous studies.
A separate study published Tuesday in JAMA Internal Medicine found that men using prescription testosterone gel, patches or injections had fewer heart attacks and strokes than non-users during about three years of follow-up. But this was only observational data in men aged 40 and up, not rigorous research testing the hormone against a placebo.
Clarifying testosterone's effects on heart problems, fractures and age-related disability will require larger, longer studies, said Dr. Evan Hadley of the National Institute on Aging. He said decisions about whether to use testosterone should take into account men's individual risks for conditions the hormone could affect.