By Chaitanya Madamanchi, M.D.:

Men who take testosterone supplements may be putting themselves at increased risk of death, heart attacks and strokes, according to a study published Tuesday in the Journal of the American Medical Association.

The new research looks at more than 8,000 male veterans with low testosterone. Researchers compared the rates of cardiovascular ills among those who'd received testosterone supplementation and those who had not, and found that men who used testosterone were 29 percent more likely to die, have a heart attack or a stroke after three years of use.

This difference could be seen even after the researchers took into account age, blood pressure, the presence of heart disease and various other factors.

More Middle-Age Men Turn to Testosterone for an 'Edge'

Testosterone supplementation is a billion-dollar industry that has experienced a more than five-fold increase from 2000 to 2011, according to the study, with U.S. doctors writing 5.3 million prescriptions each year. Men take testosterone for a variety of reasons, from the hope that it will improve their sexual function to increasing their muscle mass and strength.

Dr. Michael Ho, a cardiologist at the University of Colorado and lead author of the study, said he was surprised when he found that the risks of testosterone supplementation appeared to be the same for men regardless of whether they had existing coronary artery disease.

"This study provides some information about potential adverse effects [of testosterone supplementation]," Ho said. "This study should help inform the discussion between patient and providers about the risks and benefits before making an individualized decision."

Dr. Steven Nissen, chairman of cardiovascular medicine at the Cleveland Clinic, who was not involved in the study, said the finding underscores concerns that he and other cardiologists already had about testosterone supplementation.

"The widespread use of testosterone replacement in men is concerning, with no studies that show long-term safety," he said, adding that the findings should serve as a "warning to slow down the rush to place large numbers of men on hormone replacement therapy."

The problem, Nissen explained, is that direct-to-consumer advertising of low-testosterone treatments has led many men to ask their doctors about supplementation.

"It is now imperative that the FDA insist on large randomized controlled trials to find out if this therapy is safe or not," he said.

Dr. Anne Cappola, an endocrinologist at the University of Pennsylvania and author of an accompanying editorial to the JAMA study, said she prescribed testosterone "to those for whom it is indicated and may derive benefit," according to guidelines from the Endocrine Society.

But, she said, "a large number of men are taking testosterone, and it is not clear that all are doing so based on the right indications. … Men should make sure they are on testosterone for the right reasons, as there may be risks involved."

Companies marketing prescription testosterone supplementation defended their products. AbbVie, the company behind the popular AndroGel testosterone product, pointed to past studies suggesting that testosterone supplementation, in men with low testosterone, protects against metabolic syndrome and early death.

"FDA-approved testosterone-replacement therapies have been used to treat men with low or no testosterone (hypogonadism), who have been diagnosed by a physician, for 20 years, with therapeutic risks well documented in the prescribing labels," the company said in a statement to ABC News.

Meanwhile, Lilly, which markets Axiron testosterone gel, said it actively monitored all adverse events reported in men taking testosterone supplements.

"Axiron is a prescription medication, approved by the FDA, for men with certain conditions associated with a deficiency or absence of testosterone," Lilly said in a statement to ABC News. "Lilly does not condone the use of our medicine for off-label purposes."

Doctor's Take

For some men who are truly experiencing health effects because of low testosterone, such decreased libido, decreased strength, and low energy levels, therapies that increase testosterone levels may indeed be beneficial and improve their quality of life.

However, it's important for men to remember that these symptoms can occur even if their testosterone levels are not low. In light of this, it is important that men undergo appropriate testing to ensure that they actually have low levels of testosterone before they start treatment.

The best thing that men who are curious about testosterone supplementation can do is to talk to their doctors about all the risks and benefits rather than basing a decision on an advertising campaign.