Among sports fans, American football is considered the most popular sport in the U.S.  In the last decade, young men have trained to become physically larger so they can compete in this rough game.  But recently, doctors have been concerned that these athletes are gaining too much weight, putting them at risk of heart disease. 

Justin Bannan is a big man.  He stands at 189 centimeters [six feet, three inches] and weighs 140 kilograms [310 pounds].  As a defensive end for the Baltimore Ravens football team, he needs that weight to block his opponents.

?A lot of times you're taking on two offensive linemen at a time and, uh, these guys are huge,? Bannan said.

Bannan's size is comparable to other professional players.  The Ravens' head physician, Dr. Andrew Tucker, says for the last two decades, bigger is seen as better for linemen [offensive and defensive players who line up in forward positions].

"Being [a] larger size in the blocking scheme, as well as on the defensive line has become increasingly important," Dr. Andrew Tucker said. Dr. Tucker is the Baltimore Ravens physician.

While size has mattered on the playing field, it is also raising concerns among sports medicine experts.  Dr. Tucker has studied the risk for cardiovascular disease among 500 players in the NFL [National Football League].  

"We sort of expected that the largest, our largest athletes, the offensive, defensive linemen would compare not so favorably to the general population with respect to glucose [blood sugar] and cholesterol,? Dr. Tucker said. ?In fact our larger athletes, as well as the average NFL player, compare better than the average American with respect to glucose and comparable from lipids [fats]."

But these young athletes showed a greater prevalence of high blood pressure, compared to other men their age.  

High blood pressure can lead to heart disease, stroke and kidney failure, especially as we age and become heavier.

In a 2006 study of early mortality among players in the National Football League, medical experts suspected body weight was a factor in their deaths.  Fifty-two percent of those players died of heart problems, stroke and cancer.  Those are common problems linked to obesity.

Twenty-three year old Thomas Herrion weighed almost 150 kilograms [330 pounds] when he collapsed after an exhibition game in 2005.  An autopsy showed an enlarged heart and a coronary artery was blocked.

Forty-three year old Reggie White had retired from the Green Bay Packers when he died of a cardiac arrythmia [irregular heartbeat] in 2004.

Staying in good physical condition after those playing days are over is a concern for Justin Bannan.

"I don't think you're going to train exactly the same that you are now when you're retired, so I think you're really going to have to make some lifestyle changes just to have some good quality of life down the road," Bannan said.

The NFL study was published in the Journal of the American Medical Association.