Last weekend, I began to understand why some football players have brain injuries that can be as severe as combat vets.

I was the guest on a three-hour, live radio broadcast from Bozeman, Mont., and I was discussing the study out of Boston that found neurodegenerative brain diseases among former soldiers and athletes, but none among a control group that had no history of concussions or traumatic brain injury. One small study showed that any brain injury could increase the risk of chronic traumatic encephalopathy. Another larger study showed that professional football players were four times more likely than the general population to suffer from CTE.

Then the station got a call from Corey Widmer, and we spent the next half hour discussing his eight-year career as a middle linebacker with the New York Giants … and the number of times he got his bell rung.

“I was pretty much in the trenches for the whole time,” Widmer told me. “The middle linebackers typically aren’t covered, so you’ve got to go over the guard who tends to be a pretty big guy. The impacts are a lot more than any other position except for fullback.”

Widmer said linebackers average about 240 pounds while the guards were averaging 310 to 320 pounds.  “We’d run at each other for 10 or 15 feet, picking up some pretty fair momentum, and then collide,” he said. “We got some of the biggest impacts.”

At Montana State University, where he’s currently in the Hall of Fame, Widmer was taught to tackle with his head up. “I always got dinged around. I remember my rookie year, I hit a guy from Kansas State and we both got knocked out. We were sitting there staring at each other and waiting to see who could get up first,” said Widmer.

That didn’t change when he played professional football. “When I hit, I hit with my face, and I would literally bend the steel face mask every game,” he said. “Sometimes it would pancake the whole helmet.”

The Rydell helmets had a plastic lining that would freeze rock-solid in cold weather, he said. That was common in Montana and New York. And the turf used to freeze in Giants Stadium, so when his helmet hit the ground, his brain took another bruising.

That’s what happened when Widmer suffered a concussion so severe that the coaches held him out of the game and sent him to medical specialists for a battery of tests. Afraid of losing his job (and a million-dollar paycheck), he stormed out of the doctor’s office. Shortly after that, he found himself in the middle of a fight on the practice field.

“It was at that moment that I noticed something had changed,” he told me. “I felt more aggravated at times. It was then that I became a complete believer that concussions can change personalities.”

Widmer misses football these days, the adrenalin-charged games, the 18-hour days leading up to each game, and the responsibility for never letting his teammates down. Today, he’s looking for something as fulfilling and exciting as football.

“I used paragliding to fill the void,” he said., “It’s a pretty extreme sport.”

But five years ago, Widmer had an accident in the Chilean Andes and broke his back. While he’s back on his feet again, he needs another challenge.

Sound familiar?  This echoes the stories that scores of vets have told me about how they felt in combat and the letdown they felt when they finally got home.

“Football is basically controlled combat,” neuroscientist John Medina, author of the best-selling “Brain Rules,” told me the other day.   Widmer agrees. And the NFL is looking for ways to protect its athletes better.

There’s a study currently underway at the Boston VA Healthcare Center, where researchers are reportedly finding that some combat vets are aging more quickly than the general public.

Last week, USA Today reported that America’s newest combat veterans, former soldiers and Marines in their 20s and 30s, appear to be growing old before their time. It said scientists are seeing early signs of heart disease, diabetes, slowed metabolism and obesity that would be more common to middle age or later.

The project’s co-director, William Milberg, a Harvard Medical School professor, was quoted as saying, “They should have been in the best shape of their lives. The big worry, of course, is we’re going to have to be taking care of them until they’re in their 70s. What’s going to happen to them in the long run?”

USA Today said some form of early aging seems most common to those with signs of blast-related concussion and PTSD, which seems to involve about 30 percent of the 340 vets being studied.

It quoted Milberg as saying that researchers were initially alarmed to discover a former soldier, younger than 40, with brain lesions, obesity, high blood pressure and diabetes. When they ran the patient through magnetic resonance imaging (MRI) scans, Milberg said the scans looked like they belonged to someone in their 70s,

“That’s when we got alerted that maybe we were going to see something like these precursors we associate with old age (but) in a younger population,” he told USA Today.

That was followed by a story in UK’s Daily Mail, in which Milberg was quoted as saying that the brains of about 150 veterans showed significant signs of stress.

When I asked the VA Boston Healthcare Center for a copy of their research report, I was told: “At this time there is no report or published paper. Drs. Milberg and McGlinchey are in the process of writing up their research for peer review and publication, so we have nothing we can send you.”

I don’t doubt the veracity of the published reports, but they appear to be based on preliminary data. It will bear watching to see what the final results will show.  And there’s no indication when this data will be published.

But the results as reported would certainly be consistent with what we already know about stress.

In his best-selling book “Brain Rules,” which is a must-buy for anyone interested in understanding the human brain, Dr. John Medina notes that chronic stress leads to heart attacks and strokes. And stress ravages the immune system, leaving people increasingly vulnerable to infection.

“Not surprisingly, people who experience chronic stress are sick more often,” he wrote. “A lot more often. One study showed that stressed individuals were three times as likely to suffer from the common cold. People were especially vulnerable to the cold-producing virus if the stressors were social in nature and lasted more than a month. They were also more likely to suffer from autoimmune disorders, such as asthma and diabetes.”

Medina said stress is behind more than half of the 550 million working days lost each year due to absenteeism. “The Centers for Disease Control and Prevention asserts that a full 80 percent of our medical expenditures are now stress-related,” he added.

So if the team of Boston neuroresearchers does find that combat vets, especially those suffering from PTSD and TBI, are aging more quickly than the rest of our population, it won’t be a huge surprise. But it should be a factor in the way we fund our healthcare treatment for vets in the decades to come.

Backstopping the Boston study that was the subject of my last blog (“Disturbing New Study”), a different team of researchers reported this week that National Football League retired players are four times more likely than the general population to die of brain diseases.

Dr. Ann McKee, a pathologist and co-director of the Center for the Study of Traumatic Encephalopathy at Boston University, told the Los Angeles Times that the new research “opens new avenues for research and validates our neuropathological findings…. It raises our concern about the risk of CTE, dementia and ALS and the way these conditions overlap.”

McKee’s team studied the brains of four military vets and four athletes, all of whom had been subjected to previous concussions, and compared them with four people with no history of brain damage. All the vets and the athletes showed symptoms of chronic traumatic encephalopathy (CTE), but none of the others did, the team reported last May. After showing that they could replicate that degenerative brain disorder in blast-exposed laboratory mice, the team concluded that everyone who suffered a brain injury — even a mild concussion — could be at risk of developing degenerative brain diseases later in life that can lead to memory loss, bad judgment, depression, outbursts of anger, thoughts of suicide and potential dementia.

The new study, reported Wednesday in the journal Neurology, was much broader. A team from the National Institute of Occupational Safety and Health, which is part of the Centers for Disease Control, tracked 3,439 retired football players with five or more seasons in the NFL.

The bad news is that they found these athletes four times as likely as other men their age to die of Alzheimer’s disease or amyotrophic lateral sclerosis (ALS), better known as Lou Gehrig’s disease. And it found that the league’s speed players, those who built up more speed before they made a tackle or were brought down by one, were at even greater risk.

The good news is that the risk is still relatively small. Among the 3,439 players the researchers tracked, 1,116 died during the study period. Of those, only 27 were found to have a neurodegenerative disease as an underlying or contributing cause of death.

“Although the results of our study do not establish a cause-effect relationship between football-related concussion and death from neurodegenerative disorders, they do provide additional support for the findings that professional football players are at an increased risk of death from neurodegenerative causes,” the study concluded.

Still, it was enough to shake up the NFL, which announced on Wednesday a $30 million contribution to the Foundation for the National Institutes of Health to support “research on serious medical conditions prominent in athletes and relevant to the general population.” It was the largest single philanthropic donation ever made by the NFL in its 92-year history.

“We hope this grant will help accelerate the medical community’s pursuit of pioneering research to enhance the health of athletes past, present and future,” said NFL Commissioner Roger Goodell. “This research will extend beyond the NFL playing field and benefit athletes at all levels and others, including members of our military.”

Good for the NFL. More research is clearly needed. But we also ought to be thinking about whether we can justify risking this kind of brain damage in sports or in wars that are not clearly in defense of our homeland.

For years, we’ve known that military vets make up an abnormally large percentage of our prison population, but new studies are showing that prison inmates are seven times more likely than the general population to have suffered a brain injury.

According to Scientific American magazine, about 8.5 percent of all Americans have a history of traumatic brain injury, with about 2 percent being disabled as a result. But it said that 60 percent of the prison population has had at least one TBI, which can alter behavior, emotion and impulse control.

On average, each year that a brain-injured person spends behind bars costs taxpayers $29,000.  Then think of the lost productivity and the lost lives of more than 2 million Americans in our system of so-called “corrections.”

That’s a loss so huge that it boggles the mind.