Testosterone and Heart Attacks: Q&A
Why are the findings at odds?
"The studies are quite different in the way they are being conducted," Anawalt says.
The studies look at men of different ages and at different time periods. The Texas study focused only on men 66 or older who were on Medicare. The UCLA study looked at a wider age range of men.
Researchers have looked at different time periods to see if testosterone raises heart attack risk, says Sander Greenland, PhD, professor emeritus of epidemiology and statistics at UCLA. He was a researcher on the UCLA study and reports consultant work in various testosterone lawsuits.
His team tracked heart attacks soon after beginning the treatment. "We were looking at the first 90 days," he says.
The Texas researchers followed men between 1997 and 2005.
The men who are studied may differ in health habits, and that could affect results, Baillargeon says.
How might testosterone raise or lower heart attack risk?
The link between testosterone therapy and heart attack is complicated, Baillargeon says. Testosterone may help the heart by improving cholesterol and decreasing body fat and inflammation.
It could also raise heart disease risk in a number of ways, Baillargeon says. Men on testosterone therapy might retain more salt and water while using it, which could lead to high blood pressure and other problems, he says.
Does the research so far tip the balance one way or the other?
Experts disagree. "I think if you look at all the data in summary, there is not a clear trend towards increased risk of cardiovascular events -- stroke and heart attack, and early death -- or a clear trend toward blood clot formation [with testosterone use]," Anawalt says.
In June, the FDA added a general warning label to testosterone products, describing the risk of blood clots in the veins. The blood clot warning is not related to the FDA's ongoing evaluation of the possible link between testosterone and heart attack, according to the agency.
Greenland says the studies, overall, do show a risk. "More studies have found an association than have not," he says.
Experts do agree that, if needed, testosterone therapy can be helpful.
How is low testosterone defined, and how many men have it?
About 5 million American men have low testosterone, according to the National Institutes of Health.
Testosterone helps make sperm and maintains muscles and bones. Low testosterone can affect a man's sex drive and mood.
"Low testosterone by itself is not a disease," Anawalt says. "It is the combination of having symptoms and side effects associated with too little testosterone, plus a low blood testosterone level that you have confirmed on two or more occasions on early-morning blood tests."
Blood levels of testosterone change throughout the day.