"We don’t know yet whether normalizing the [testosterone] level will reduce the excess risk we identified in our paper, but many studies have shown that you will feel better," study leader Kevin S. Channer, MD, tells WebMD.
But observational studies like Channer's can be misleading, notes William O'Neill, MD, professor of cardiology at the University of Miami Miller School of Medicine. O'Neill, who was not involved in the U.K. study, warns that only a clinical trial can prove whether hormone replacement therapy can improve heart health.
"There is no proof that fractures or cancer or heart disease significantly improve for men on testosterone replacement therapy," O'Neill says. "A lot of men want to feel younger and more virile and have more sex drive. In this regard it is similar to estrogen replacement for middle-aged women. They feel more youthful and have better vaginal tone, but other long-term benefits aren't proven."
What the study does show, O'Neill says, is that low testosterone can identify men at risk of heart disease.
"So you go to your doctor and check your testosterone level and it is low. Now it looks like you are at risk of heart disease," he says. "But there are a lot of well-known, well-established things you can do to lower risk of heart disease: Lose weight, lower your blood pressure, exercise, stop smoking, and lower your cholesterol."
The link between low testosterone and heart disease applies only to men. Women with high testosterone levels are at increased risk of heart disease.
In a way, the new findings are ironic. Researchers once thought that the female sex hormone estrogen was the reason why women have relatively less heart disease than men do. Now it appears to be the male sex hormone testosterone that protects men.
The U.K. study shows that free testosterone measurements are a better measure of heart risk than are total testosterone measurements. But O'Neill says that in most cases, total testosterone will give doctors a good idea of a patient's heart risk.
In an editorial accompanying the Channer study, Ronald C.W. Ma and Peter C.Y. Tong of the Chinese University of Hong Kong call for clinical trials to investigate whether testosterone replacement therapy can lessen men's heart risk.
Ma and Tong warn, however, that too much testosterone is clearly a heart risk, and that the goal of testosterone replacement should be to approximate -- not to exceed -- normal testosterone levels.
The Channer study, and the Ma/Tong editorial, appear in the Oct. 20 online issue of the journal Heart.