A new study designed to shed light on the dangers that some of the largest pro football players face has been dismissed by the National Football League.

The Scripps Howard News Service study investigated the 3,850 deaths of professional-football players in the last century.

The study concludes that the heaviest athletes are more than twice as likely to die before their 50th birthday than their teammates.

Most of the 130 players born since 1955 who have died were among the heaviest athletes in sports history, according to the study. One-fifth died of heart diseases, and 77 were so overweight that doctors would have classified them as obese, the study found.

"Clearly, these big, fat guys are having coronaries," said Charles Yesalis, a Penn State professor of health policy and sport science.

But in a statement, NFL spokesman Greg Aiello dismissed the Scripps Howard study, saying: "The issue of obesity in our society transcends sports and must be dealt with in a comprehensive, responsible way. This media survey contributes nothing."

Scripps Howard compared the mortality rates for professional-football players with the 2,403 Major League Baseball players who have died in the last century. The comparison found that football players are more than twice as likely to die before age 50.

The average weight in the NFL has grown by 10 percent since 1985 to a current average of 248 pounds. The heaviest position, offensive tackle, went from 281 pounds two decades ago to 318 pounds.

The Scripps Howard study used the body-mass index to determine whether a player was obese. The NFL has previously decried the standard for not distinguishing between muscle and fat.

More than 500 players on NFL training-camp rosters last summer were listed as weighing more than 300 pounds, an exponential increase in the past two decades.

In the pre-season, San Francisco's Thomas Herrion collapsed and died after an exhibition game. A Denver coroner concluded the 315-pound player had an enlarged heart and blockage of the right coronary artery.

Medical experts say that in addition to coronary artery disease, the combination of size and extreme lifestyle put players at risk of hypertension and disease.

At a memorial service for Herrion, NFL Commissioner Paul Tagliabue pointed out that he already had asked medical experts to study the cardiovascular health of players.

"We need to understand in a serious way what the risks are, to the extent that there are risk factors," Tagliabue told reporters. "We've got to address them. We are working on it."

The study has yet to be completed.

A 1994 study conducted by the National Institute for Occupational Safety and Health, conducted at the request of the NFL Players Association, found that while players generally weren't dying sooner than average, offensive and defensive linemen had a 52 percent greater risk of dying from heart disease than the general population.

The NFLPA declined to comment on the Scripps Howard survey.