The study, reported in the American Journal of Cardiology, followed more than 3,400 NFL players who were active between 1959 and 1988. It found that 334 had died by 2007 -- only about half the rate that would be expected based on U.S. norms.

But certain players -- the ones who were biggest during their careers -- had higher risks of dying from heart disease or stroke.

Defensive linemen, in particular, had a 42 percent higher risk of death from cardiovascular disease compared with U.S. men in general.

Of 498 defensive linemen, 41 died of cardiovascular causes.

The findings build on evidence that football players' big bodies can become a health liability in the long run, according to Dr. Sherry L. Baron, a researcher at the National Institute for Occupational Safety and Health in Cincinnati, Ohio, who led the study.

Often, professional athletes' muscle mass can make for a high body mass index (BMI) -- a measure of weight in relation to height.

And there's the argument that a high BMI based on muscle is not so bad, Baron pointed out in an interview.

"But I think this makes it clear that if you're big and muscular at a young age, it could have a long-term (health) effect," Baron said.

The problem, she noted, is that once big athletes are no longer in the game, it's very hard to keep up their former physical activity levels. Sometimes, injuries can make it physically impossible.

Other studies have found that after retirement, pro football players tend to have more heart risk factors -- like high blood pressure, unhealthy cholesterol levels and obesity -- than the general public.

And that research, too, suggests that body size is the culprit.

Besides the findings on defensive linemen, the current study showed that players with a BMI of 30 or higher during their careers -- which would qualify them as "obese" -- were twice as likely to die of cardiovascular causes as their lighter peers.

The study does have limitations, according to Dr. Martin Goldman, a cardiologist at Mt. Sinai Medical Center in New York who has studied NFL players' heart risks.

One, he told Reuters Health, is that it relied on information from death certificates, which does not always give the whole picture. A death from a drug overdose, for example, can be classified as a heart disease death.

There are also a lot of other unknowns, Goldman said. The researchers don't know how players' BMIs changed over time, or what kind of lifestyle they led after retirement.

Those factors are presumably important, but it's not clear from this study what role they had in big players' later risk of heart disease death, Goldman noted.

Still, Goldman said the bottom line seems to be that size matters.

"I think body size is the important thing here," he said. The big players, Goldman added, need to make an effort to "get down in size" once they are not longer in the game.

That means cutting down substantially on calories -- since many players, Goldman noted, get used to eating a lot to keep up their high activity levels and muscle mass.

"They don't necessarily change their eating habits, even though they're not exercising as much," he said.

Both Baron and Goldman said there are implications beyond the NFL. Many of today's college and high school football players bulk up substantially -- and there's evidence from some studies that it can boost their risk factors for heart disease later on, Baron said.

"Young athletes may strive to look like the professional players," Baron said, "but they need to realize there could be long-term health effects."

For its part, the NFL has responded to the issue of retired players' heart health, Baron noted.

Since 2007, the NFL Player Care Foundation has funded free heart screenings for retired players, as part of a larger research project.

SOURCE: bit.ly/xPPpyF American Journal of Cardiology, online January 27, 2012.

• A Permanent Economic Emergency