Findings published in the Journal of the American College of Cardiology showed that of 2,400 Swedish men in their 70s and 80s, those with the highest testosterone levels were less likely to suffer a heart attack or stroke over the next several years than men with the lowest levels.
But the results do not prove that testosterone itself deserves the credit, and it's too soon to recommend testosterone replacement to try to lower heart risks.
"What we can say is that elderly men with high testosterone levels are relatively protected against cardiovascular events, and therefore lower testosterone is a marker for increased cardiovascular risk," said Asa Tivesten, at Sahlgrenska University Hospital in Goteborg, Sweden, who led the study.
It's known that any serious health condition can lower testosterone levels, as can obesity. But in the study, the researchers accounted for a number of health factors -- including the men's weight, blood pressure and any diagnoses of diabetes, heart disease or stroke at the outset.
Of 604 men in the bottom quarter for levels of the "male" hormone at the study's start, 21 percent had a heart attack, severe chest pain or stroke over roughly five years.
That compared with roughly 16 percent of the 606 men who started out with the highest testosterone levels.
Even accounting for health factors, men in the highest-testosterone group still showed a 30 percent lower risk of heart disease or stroke compared with the other three-quarters of the study group.
But that doesn't rule out the possibility that something other than testosterone may be at work, said JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital in Boston, who was not involved in the study.
"Low testosterone may be a marker of other health conditions that put men at higher risk of cardiovascular disease," she said.
Potential reasons for why higher natural testosterone levels may be good for the heart include the fact that higher testosterone generally means less body fat and more lean muscle.
What's needed, she added, is evidence from clinical trials that actually test whether testosterone replacement in older men cuts the risk of heart disease and stroke.
Those trials are ongoing and so far, she noted, the results are mixed on whether testosterone replacement improves "intermediate" outcomes like cholesterol or blood sugar levels.
No one yet knows if it affects the ultimate outcomes of cardiovascular disease and lifespan.
"There are many unanswered questions, and I don't think this means that men should be trying to boost their testosterone with testosterone replacement therapy," she said.
The experience with hormone replacement therapy (HRT) in women offers a cautionary tale.
Before 2002, many women used HRT in the hopes of warding off heart disease and osteoporosis. Then a large U.S. clinical trial found that women given pills containing estrogen and progesterone actually had higher risks of blood clots, heart attack, stroke and breast cancer than women given placebo pills.
Now HRT is largely used only for treating severe hot flashes -- and then, only at the lowest dose and for the shortest time possible.
"So there are concerns about the risks in men," Manson said.
Among those are the potential for testosterone to contribute to blood clots, liver damage or prostate cancer.
"This is a study of endogenous (natural) hormone production. It does not provide information about what is happening when hormones are given as a therapy," Tiveston said.
