Men aged 40 or over with low levels of testosterone may be at increased risk of fatal heart attacks or death from any cause, a British study suggests.

In fact, "The magnitude of the effect was very similar to that of [high] cholesterol or blood pressure," said lead researcher Dr. Kay-Tee Khaw, professor of clinical gerontology at the University of Cambridge School of Clinical Medicine.

However, more work is needed to see whether testosterone supplements should be recommended for men with naturally low levels of the hormone, she said.

"We need to replicate these findings," Khaw said. "We hope we can entice other investigators to look at testosterone levels and see if these findings are confirmed."

Her team published the findings in the Nov. 27 issue of Circulation.

The study included more than 11,600 men ages 40 to 79 who were free of known cardiovascular disease and cancer at the start of the trial. It was done because "there have been lots of studies suggesting that low testosterone may not be good for health," Khaw said. "So, we wanted to see if this could be demonstrated in a large population. Testosterone is hard to measure, the test can be expensive."

The men were divided into four groups based on their blood testosterone levels.

Those men in the highest quarter of testosterone readings -- with at least 19.6 nanomoles of the hormone per liter of blood -- had a 41 percent lower risk of dying over 10 years than those in the lowest quarter of testosterone readings -- less than 12.5 nanomoles of testosterone per liter of blood.

One major question is whether low testosterone is a risk factor itself or just a marker for other risk factors, said Dr. Victor Montori, associate professor of medicine at the Mayo Clinic in Rochester, Minn. He has done his own studies on testosterone replacement therapy.

"It does not mean that replacing or normalizing levels of testosterone would reverse the outcome," he said. "There are other hormones in the blood that are related to other risk factors, such as diabetes and hypertension."

In any case, a testosterone replacement regimen "would not be a walk in the park," Montori said. "It would be a major intervention."

According to Dr. Jorge Plutzky, director of the Vascular Disease Prevention Program at Brigham and Women's Hospital in Boston, the experience of women taking hormone replacement therapy (HRT) shows that hormonal regimens can have their dangers.

Beginning in the 1990s, millions of older American women took HRT, which replaced two female hormones, estrogen and progestin. Early trials had indicated that the therapy might reduce the risk of cardiovascular diseases such as heart attack and stroke in older women.

Instead, the Women's Health Initiative, a major study released in 2002, found that women taking HRT were at increased incidence of stroke, blood clots and breast cancer, noted Plutzky, who is also a spokesman for the American Cancer Society. HRT prescriptions dropped off precipitously after the study's release.

So, much more research is needed on the link between testosterone levels and mortality before doctors can recommend the regimen to men, Khaw said. Such studies might provide "insights and better understanding of disease mechanisms, such as how and why testosterone might be related to poorer health through, for example, insulin metabolism, lipid metabolism or inflammation," she said.