Five new US clinical studies on testosterone treatments for older men showed mixed results on whether the male hormone therapy carries cardiovascular risks, according to research published Tuesday.
The US Food and Drug Administration in 2015 stepped up its warning about testosterone products, saying they could increase the risk of heart disease and heart attacks.
Four of the five studies, part of the Testosterone Trials or TTrials, looked at the effects of testosterone in gel form compared with a placebo on men 65 and older.
The TTrials involved 788 participants with low testosterone levels seemingly due to age only. They were conducted in 12 US teaching medical centers across the country for a year and were mainly funded by a grant from the National Institutes of Health.
A fifth study, not part of the TTrials, looked at the link between testosterone replacement therapy and cardiovascular effects. The observational study focused on 8,808 men 40 and older over three years.
The results were published Tuesday in the Journal of the American Medical Association (JAMA).The scientists in the TTrials studies found that after one year of testosterone therapy, bone density and strength of the men improved and anemia was reduced.But the therapy may worsen plaque in coronary arteries, the researchers warned.
There was a 20 percent increase in the build-up of plaque within the walls of blood vessels in the heart during the year.
Taken together, the TTrials "do not materially change the unfavorable balance of safety and efficacy to initiate testosterone treatment" in older men, wrote David Handelsman, a doctor at the University of Sydney in Australia, in an editorial published in JAMA. "Low testosterone levels due to obesity and other aging health problems are better addressed by lifestyle measures" directed at those problems, Handelsman said, also warning of cardiovascular risks for women taking testosterone.
In another JAMA editorial, Eric Orwoll, a professor of medicine at Oregon Health & Science University, noted that the TTrials did not address the critical issues of whether there are important long-term adverse effects.
"At this point, clinicians and their patients should remain aware that the cardiovascular risks and benefits of testosterone replacement in older hypogonadal (low testosterone) men have not been adequately resolved," Orwoll wrote.
Thomas Gill, a professor of medicine at the Humana Foundation and a lead author of the research, said the latest studies demonstrate that if a man with low testosterone is prescribed the hormone for diminished sexual function, he may have some additional benefits on hemoglobin levels and bone density.
"Looking globally at testosterone therapy, the strongest evidence is for sexual function," Gill said.
While the outcome of the cardiovascular trial raised concern, he said, a larger and longer study would be needed to determine the clinical significance of the findings.