San Francisco 49ers center Jeremy Newberry has played seven seasons in the NFL. A large, menacing-looking man who is listed at 6 feet 5 and 310 pounds in the team's media guide, he knows the sport allows little room for self-doubt.

But as he stood outside the 49ers' locker room at their Santa Clara, Calif., training complex this week, days after teammate Thomas Herrion collapsed and died following a preseason game in Denver, Newberry expressed reservations about his weight and profession.

"I think the life expectancy for offensive linemen isn't great," Newberry said. "For me, having young children, it's a somber thought. But it's part of the job."

The cause of Herrion's death has not been determined. It's possible an ailment like a previously undisclosed heart condition killed him. Herrion's father suffered from diabetes and died last year of a stroke, and his mother suffers from high blood pressure. Still, many observers, including 49ers offensive linemen, wonder whether Herrion's weight was a factor. He was listed at 6-3 and 315 pounds, and his agent said he'd been 15 to 25 pounds heavier than that last season.

The NFL was concerned even before last weekend about whether players are obese and at greater risk for serious health problems. Commissioner Paul Tagliabue appointed a group of medical experts to collect data and study the cardiovascular health of players, but that process isn't completed.

"There's a rush to judgment that his death was related to his obesity, and that's an open-ended question," said Elliot Pellman, the chairman of the New York Jets' medical department and the NFL's medical liaison. "We're trying to answer the questions: Is there obesity in the NFL? And if there is obesity, are the players at more or less or the same risk as their counterparts in the real world? Those are questions we have to answer."

Tagliabue attended a memorial service Tuesday night for Herrion, who was 23, and told reporters: "We need to understand these guys are bigger than most people in society. They are fitter than most people in society, and their jobs are more demanding. . . . We need to understand in a serious way what the risks are, to the extent there are risk factors. We've got to address them. We are working on it."

The NFL game has become one of behemoth linemen. A 300-pound player was a rarity in the late 1980s. But there were 552 players listed at 300 pounds or more on NFL training camp rosters this summer; another 82 players were listed between 295 and 299 pounds. The Cleveland Browns, Green Bay Packers and Houston Texans each had 23 players weighing at least 300 pounds to lead the league. The Jets had the fewest 300-pounders, with nine. Many of those players will be cut, but most accounts place the number of 300-pounders who played in the league last season at about 350.

A 2003 study by University of North Carolina endocrinologist Joyce Harp, published in the Journal of the American Medical Association, said that 97 percent of NFL players were overweight and 56 percent qualified as obese (30 pounds or more over a healthy weight). She took the heights and weights of 2,100 players as listed on the league's Web site and calculated the players' body mass index using the government standard based on height and weight.

Harp wrote "the high number of large players was not unexpected, given the pressures on professional athletes to increase their mass. However, it may not be without health consequences," citing previous studies that documented obesity-related problems, including sleep apnea, high blood pressure and other cardiovascular problems.

"The high prevalence of obesity in this group warrants further investigation to determine the short- and long-term health consequences of excessive weight in professional as well as amateur athletics," she wrote.

Many people, including NFL officials, believe the study was flawed because it fails to take into account a player's muscle mass and percentage of body fat.

"It's okay if you're an actuary for life insurance," Pellman said of BMI. "But medically, we don't define obesity that way. It's not designed for people that large. The study the commissioner has ordered will do a lot more than take heights and weights off the Internet. The data must be gathered in a scientific way."

Said 49ers Coach Mike Nolan: "If you put 300 pounds on my body, you have an obese man. If you put 300 pounds on some of our players' bodies, you don't."

A national report released this week based on data by the Centers for Disease Control and Prevention between 2002 and 2004 said that 22.7 percent of adults nationwide are obese, up from 22 percent for 2001 to 2003. The NFL certainly recognizes the scope of the problem: In 2003, the league announced it was giving a $2 million grant over four years to help combat child obesity nationwide.

Asked what he believes the results of the NFL's study eventually will show, Pellman said: "What I would say is, there is an obesity problem in the United States. I believe when you take the total NFL population and match it up to the general population, the NFL will be less than the general population. But we don't have the data yet."

Steven Blair, the president and chief executive officer of the Cooper Institute, a health and fitness organization in Dallas, said his organization's studies show no increased mortality rate among people who fall under the obese category of BMI if they also are physically fit.

"You have to be concerned" about Herrion's death, Blair said. "But this was a seemingly healthy young man, and to say it's because he was 300 pounds is absurd in my opinion. I remember in the old days when Roger Brown, who played for the Lions, was the only 300-pounder in the league. But in the old days, weight training was not part of their regimen. I see around the league a lot of muscular people. Occasionally you'll see the pot bellies, but it's complete and utter nonsense that there are that many obese and overweight players."

But other outsiders also say that NFL linemen are overweight to an unhealthy degree.

"There's no question that the super-sizing that's occurred in the NFL, college and high school the last 30 years has tipped the scales in a negative way," said Arthur (Archie) Roberts, an all-America quarterback at Columbia who played three NFL seasons in the 1960s before becoming a cardiac surgeon.

"It means there is a serious alert for a health imbalance," Roberts said. "The real problem is what's happening inside these men to their cardiovascular risk factors. The combination of large body size is associated with increased risk factors for diabetes and hypertension, which lead to so many other problems. Doctors have learned over the last 30 years that so many bad outcomes are related to cardiovascular problems that might have been avoided."

Roberts now heads the New Jersey-based Living Heart Foundation, which is working with the NFL Players Association on a study of past and present players, trying to assess the cardiovascular health consequences of excess weight and other issues. "Cardiac arrest in the locker room is tragic but, thank God, a rare event," Roberts said. "But many of the risk factors that are in these players' bodies are not apparent now but will be apparent later in life. We have to shift the pendulum and evaluate and educate the younger players, make it a total process.

"With retired players we're finding high cholesterol and high blood pressure. We already know sleep apnea is associated with heart arrhythmia and hypertension. You have a lot of risk factors building in players. We have to make them aware and start educating them on how to take care of themselves to avoid problems later on. We have the technology to do it. We have a support system of doctors and hospitals involved in this study willing to do it. It's now a matter of getting players to buy into it. This is not mystical."

Roberts said the problem extends to the high school level. "Many high school kids are also super-sizing with the dream of playing in the NFL," he said. "We're finding increases in deaths at those levels. We used to have 30 to 40 sudden cardiac deaths a year in all sports. There's a national registry now and the number is close to 300. About 80 percent of those are in football and basketball. Something is going on. It's the evolution of cardiovascular disease and its risk factors, one of which is large body size."

Mackie Shilstone, a New Orleans-based athletic trainer who said he has worked with more than 300 NFL players, including 20 linemen, over the past 10 years, believes players are putting their lives at risk by being so heavy.

"When I talk to these linemen, I ask them, 'How long have you been this big and fat?' " Shilstone said. "Most of them say it goes back to high school. They carry so much fat around their midsection, and you do it for so many years, you have big problems down the road. . . . These guys are playing in the shadow of death. Later in life, these guys won't make it. Heart disease doesn't care who you are or how much money you make. It will take you out.

"It's men playing a child's game and death should not be part of the equation."

Shilstone said he once worked with an NFL player who had high blood pressure (190/110), elevated cholesterol and a blood sugar level that qualified him as a diabetic. After losing 34 pounds, his health improved.

Shilstone said he thinks overweight players are a far bigger concern than other issues that get more publicity, like steroids. "If you saw these guys on the street in regular clothes and asked what do you think of that guy, you'd say he's a fat man," he said. "We have to give them far more nutritional counseling. The problem is the players don't always listen. Age is mandatory; maturity is optional. We're not dealing with a lot of mature people here.

"What's amazing to me is that I've never heard a team say we want you to come in big and fat. We have to give these players guidelines on what is acceptable in terms of body fat. I kept Lomas Brown in the game for 18 years at 278 pounds, with 16 percent body fat. It can be done."

But players say all that it takes is a quick look around the locker room to realize that the days of the 270-pound offensive lineman in the NFL are gone. The league's pass-blocking rules allow offensive linemen to use their hands far more, so the old-time emphasis on athleticism and footwork was replaced by brute strength and girth.

When Newberry, the 49ers' center, was asked this week what the solution to the prospective health woes of linemen is, he said: "Try to play at 200 pounds." He quickly added: "But that ain't going to happen."

Former NFL great Reggie White died in December at age 43 because of respiratory disease and other health problems that may have been complicated by his sleep apnea. A study in the New England Journal of Medicine done two years ago of more than 300 NFL players revealed an unusually high rate of sleep apnea (14 percent, as opposed to 4 percent of the general population). It climbed even higher for linemen -- to 34 percent. Newberry said he knew when White died that he, too, suffered from sleep apnea; he said he even had stopped breathing for short periods while on the operating table undergoing previous surgeries for other injuries. Newberry said he's also had blood-pressure problems. Ongoing knee problems have his football future in doubt but he's not yet ready to retire, as his worried mother and wife might like him to do. But with one young daughter and another child on the way, the news about White's death led Newberry to undergo surgery this past offseason to correct his sleep apnea. Suddenly, he was more concerned than ever about his health.

"I had my first child," he said, "and I wanted to stick around a lot longer."

A 2003 study reported that 97 percent of NFL players were overweight and 56 percent were obese. "We need to understand in a serious way what the risks are," Paul Tagliabue said. Thomas Herrion "was a seemingly healthy young man, and to say [he died] because he was 300 pounds is absurd," said Cooper Institute's Steven Blair.