Higher naturally occurring levels of the male hormone testosterone appear to protect men from fatal heart attacks or strokes and death from all manner of causes, researchers in Britain said on Monday.
But the researchers cautioned men not to begin testosterone supplementation based on the results of this 10-year study, saying the benefits and risks are unclear.
The role of testosterone in men's health is controversial, with the relationship between men's natural testosterone levels and overall health not well understood, according to the researchers.
But this study led by Dr. Kay-Tee Khaw, a professor of clinical gerontology at the University of Cambridge School of Clinical Medicine in Britain, found strong benefits in men with higher natural levels of the hormone.
Men in the upper 25 percent of natural testosterone levels had a 41 percent lower risk of dying from heart attack, stroke and other cardiovascular conditions, cancer and all other causes, compared to men with the lowest levels, the researchers found.
"Low testosterone seems to predict increased risk of total mortality in cardiovascular disease as well as cancer," Khaw said in a telephone interview.
The researchers tracked 11,606 British men ages 40 to 79 who had no known cancer or cardiovascular disease at the start of the study. They joined the study from 1993 to 1997 and were followed until 2003.
Among these men, 825 died during the study period. The researchers measured their testosterone levels using frozen blood samples provided earlier, and compared their levels to a group of men still alive at the end of the study period.
Khaw said the relationship between testosterone levels and cardiovascular disease mortality was comparable in magnitude to well-established risk factors like high blood pressure and cholesterol levels.
Thus, low testosterone levels could point to men at elevated risk for cardiovascular death who may not have other known risk factors, the researchers reported in the journal Circulation.
Khaw said the findings suggest that men with low levels of testosterone might be able to cut their risk of death with testosterone supplementation, but did not recommend doing this without more research backing up these results.
She pointed to the experience involving hormone therapy in women. Early studies suggested hormone therapy could protect post-menopausal women from heart disease, but later and larger research yielded the opposite results.
"The anxiety about testosterone supplementation is that high testosterone may be a risk factor for prostate cancer," added Khaw, who noted that the study looked only at naturally occurring levels of the hormone and not supplementation.
Testosterone is the primary "male" hormone that helps maintain muscle mass and strength, fat distribution, bone mass, sperm production, sex drive and potency. Women have testosterone too, but at lower levels.
Doctors have used testosterone therapy to treat men with abnormally low testosterone levels. Some athletes and bodybuilders use it to promote muscle mass and strength.