The most extensive examination to date of deceased athletes’ brains shows that most had signs of brain damage after suffering repeated head injuries — including two high school football players who died in their teens.

Being published Monday by Boston University School of Medicine researchers, the study reports on the autopsies of 85 brain donors, most of them professional athletes. It comes as concerns mount over the dangers of head injuries in contact sports and some call for banning tackle football for younger children.

The work provides new insight into an Alzheimer’s-like condition, called chronic traumatic encephalopathy, that is thought to be caused by repeat concussions or blows to the head. The autopsies revealed extensive evidence of protein tangles called tau clogging brain tissue and causing the destruction of brain cells in football players, wrestlers, hockey players, boxers, and military veterans who served in combat zones.


“The sheer size of our study should make any doubters no longer doubt’’ that CTE is a real condition caused by repeat head injuries, said study co-author Dr. Robert Cantu, a neurosurgeon and co-director of the BU Center for the Study of Traumatic Encephalopathy.

These findings could prove helpful to the mega lawsuit against the National Football League filed last spring by thousands of former players and their families, who claim that the National Football League hid information that linked football-related head injuries to dementia, depression, and other cognitive problems. It also underscores the potential dangers of youth football, months after a September Pop Warner game played in Central Massachusetts resulted in five concussions for 10- to 12-year olds.

Some neurologists, however, emphasized that there’s still reason for skepticism about whether multiple blows to the head really do lead to tau tangles. “Yes we can all agree now that this is a real brain condition, but we don’t all agree on whether multiple concussions cause the emergence of this entity,’’ said Peter Warinner, director of sports neurology at Brigham and Women’s Hospital who heard the study findings presented at a recent research conference in Switzerland.

The researchers reported in the journal Brain that 68 of the 85 individuals they examined, all of whom had experienced repeated head trauma, had evidence of CTE. But they cautioned that the study was not designed to establish the frequency of this type of brain damage in athletes. They didn’t see any signs of tau in the brains of 18 controls, who were matched by age and had never experienced concussions or other brain injuries.


Symptoms of CTE were first described in retired boxers in the 1920s and have been documented in football players, hockey players, boxers, military veterans, and those with a predilection for head banging. While the condition hasn’t been found in the brains of those without head trauma, Warinner said that could simply be due to the fact that it’s rare and that more brains in the general population need to be autopsied.

The new study described four stages of the disease, noting that symptoms can progress for years after head trauma. It starts with headaches and problems with concentration in the early stages, followed by depression, aggression, explosive anger and short-term memory loss. Then comes more serious cognitive impairment, and eventually full-blown dementia where a person doesn’t recognize loved ones.

Athletes and military veterans who experienced such symptoms before they died donated their brains for further research. “We’re not studying a group that went on to live productive lives after their football or military careers,’’ said Cantu. “Those who decide to have their family member’s brain studied want to figure out what went wrong near the end of his life.’’

Study leader Dr. Ann McKee, a BU neurologist who directs the Bedford VA Medical Center brain banks used for the study, said certain genetic factors most likely combine with the number and severity of head blows through a person’s lifetime to determine the likelihood of developing the condition, which has no treatment and no diagnostic test beyond an autopsy.


Bolstering the evidence that lasting brain damage can occur from repeat concussions, the study found that the damage seen in an autopsy was far more extensive in athletes who died after age 50 and who played professionally in contact sports such as boxing, football, or hockey. These players also exhibited more severe memory loss and personality changes before they died.

“I think what this study says is that if individuals play football — especially if they have concussions that aren’t properly managed — they can develop areas of brain damage,’’ said McKee. What’s not known is just how many head impacts are too many. McKee said finding early signs of tau deposits in the brains of the two football players who died in high school doesn’t necessarily mean that the damage they sustained would have been permanent if they stopped playing football soon after their teens.

High school football player Nathan Stiles — who died in 2010 after bleeding occurred in his brain during a football game — had early signs of CTE in his brain when it was autopsied as part of the study. The 17-year-old didn’t die from that condition but from the brain bleed, likely caused by an earlier concussion that hadn’t had time to fully heal before Stiles was tackled in subsequent games.

Ron Stiles, Nathan’s father, said he still wonders why his son died when they followed all the rules: Nathan sat out of practices and games for three weeks after his concussion, and he had no lingering symptoms and received his doctor’s consent before resuming play. He also had no signs of bleeding on a brain scan after the concussion.

“We sent the scans to Boston after we donated his brain, and the researchers told us absolutely nothing was there,’’ said Stiles, who lives with his wife and daughter in Spring Hill, Kansas. “It’s definitely a good thing to do the research and try to get better understanding of this.’’

The new study is sure to prompt renewed calls for restrictions on children playing contact sports, but much is still unknown about the dangers to youth. Cantu said he’s in favor of replacing tackle football with flag football for all children under age 14 since their developing brains may be more vulnerable to impacts, but Warinner said there aren’t any studies to suggest that such a restriction would prevent long term harm to the brain.

The 2010 Massachusetts concussion law has raised awareness about the dangers of putting high school players with concussions back into practices and games before the brain has time to heal and mandates that doctors sign off before a player can return after a concussion. Cantu, however, would like to see high school teams adopt the new NFL rule that limits contact practices, which involve tackling, to once per week during the regular season.

“There’s no talk of setting up formal rules for limiting contact practices,’’ said Paul Wetzel, spokesperson for the Massachusetts Interscholastic Athletic Association, a nonprofit organization that represents more than 370 high schools in the state. “But most football coaches will tell you that two or three games into the season, they’re limiting contact practices to avoid injuries.’’

Pop Warner decided to limit contact practices this year, said Jon Butler, the organization’s national executive director, and prohibits players with concussions from returning to practices and games without a doctor’s consent.

The league for 5- to 14-year olds also has rules to prevent serious head injuries from occurring during a game, but that doesn’t mean coaches always follow them. The Central Massachusetts game that led to multiple concussions was a “clear violation of Pop Warner’s rules,’’ said Butler in allowing lopsided teams with more players on one side than the other. “That game should have stopped three to four minutes after it started.’’