A new report concludes that low levels of the sex hormone might raise men's risk of dying from heart disease.
Researchers followed more than 3,600 elderly men living on their own for about five years on average. Over that time, about 6% died of heart disease, with higher mortality in men with lower levels of free testosterone.
The results add to a confusing tangle of data. Some show low testosterone levels are linked to earlier deaths, including those due to heart disease, while other data don't.
Pharmaceutical companies are also promoting testosterone therapy for problems like grumpiness, lack of energy and decreased libido.
Causation versus correlation
The main problem in this area – the question of causation versus correlation – is one that also mars the new report, according to Dr Frederick Wu, who wasn't part of the study.
"Low testosterone is associated with poor health," Dr Wu, a hormone expert at the University of Manchester in the UK, said. "But it does not mean that low testosterone is the cause of poor health or increased mortality."
Earlier this year, a large meat-analysis concluded that declines in testosterone are unlikely to shorten a man's life span, but instead might be related to declining health.
Zoe Hyde of the Western Australia Centre for Health and Ageing, who worked on the latest study, said that was not a likely explanation when it comes to heart disease.
"There is good evidence that testosterone has beneficial effects with regard to the cardiovascular system.
For example, testosterone has been shown to increase lean mass (including muscle), whilst decreasing fat mass. It can also have some positive effects on cholesterol levels," she said.
The researchers, who published their findings in the Journal of Clinical Endocrinology & Metabolism, did adjust for various risk factors.
But that still doesn't prove low testosterone is harmful to the heart, according to Dr Wu. "This conclusion is somewhat premature," he said.
One recent clinical trial that tested a testosterone gel on elderly men had to be stopped early because the drug turned out to cause heart problems – not prevent them.
Hyde acknowledged that her study is not definitive. "We need to wait for the results of clinical trials before we can properly understand both the benefits and also the risks of testosterone therapy," she said.
(Reuters Health, Frederik Joelving, November 2011)