Head trauma has become an existential question for football — and people have long wondered how common brain disease is for players of the sport.
A new study published Tuesday begins to answer: for NFL players, at least 25 percent of those who died over a recent six-year period had the neurodegenerative disease known as CTE, though researchers believe the true rate is likely even higher.
Researchers who analyzed hundreds of cases found that at least one in four ex-NFL players who died from 2016 to 2021 had chronic traumatic encephalopathy, or CTE, at their time of death. The study, conducted by experts at Mass General Brigham, Boston University, and the Concussion & CTE Foundation, highlights the safety issues in a popular sport played by scores of college athletes and roughly 17,000 high school students in Massachusetts.
To continue reading, please login or subscribe to Globe.com
“Although this study was just looking at former professional football players, these athletes didn’t just get their head impact exposure at the professional level,” said Dr. Daniel Daneshvar, the study’s lead author and chair of physical medicine and rehabilitation at MGB. “They got exposed to head impacts at the collegiate level, at the high school level, and in many cases, the youth level. All of those hits accumulated to increase their risk of having this pathology in their brain.”
Daneshvar called the findings a “wake-up call.”
Among the general population, CTE affects less than 1 percent of people. According to the study’s results, in a 50-person professional football team, at least 12 players could develop CTE, Daneshvar said.
“To see that, at a minimum, 25 percent of NFL players have this pathology in their brain when they die, that means that we need to move towards how to treat this disease and how to cure it for these individuals,” said Daneshvar, who has treated NFL players with dementia.
In 2017, researchers said they found CTE in 110 of the first 111 brains of former NFL players that had been donated at that point. The new study allows researchers to estimate how many CTE cases could be expected among all NFL players, not just those whose brains were donated to science.
The NFL began removing players with suspected head trauma from games in 2009, four years after Dr. Bennet Omalu published a paper identifying CTE in the brain of former Pittsburgh Steelers center Mike Webster, whose autopsy he performed in 2002. The NFL initially denied — and tried to discredit — Omalu’s research, which became the subject of the 2015 movie Concussion, starring Will Smith.
In 2009, a spokesperson for the league acknowledged that concussions can lead to long-term problems.
The stories of football players suffering in their retirement years are legion. The 2001 Patriots had seven former players die between the ages of 35 and 50.
In 2012, former Patriots linebacker Junior Seau died by a gunshot wound to the chest, a decision he made to preserve his brain for research. He was found to have Stage 2 CTE. Former Patriots tight end Aaron Hernandez, who died by suicide in 2017 while serving a life sentence for murder, was found to have the most advanced CTE case (Stage 3) for someone his age (27).
Amid a class-action lawsuit filed by some 5,000 former players in 2013, the NFL mandated independent “concussion spotters” on sidelines. The league settled the suit for $1 billion in 2015.
In a statement Tuesday, an NFL spokesperson emphasized the league’s commitment to supporting the physical and mental wellbeing of its players.
“The NFL continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts,” the spokesperson said.
CTE is a progressive neurological disease likely caused by repeated head injuries, including concussions as well as smaller impacts. While the disease is most often associated with football players, other athletes, including hockey, rugby, and soccer players, are also at risk. CTE has also been found in the brains of people in the military.
Symptoms can include cognitive impairment, such as memory loss, as well as behavior and mood changes, which can be severe.
The disease can only be definitively diagnosed after death by analyzing brain tissue.
In the new study, Daneshvar and his team examined more than 1,700 NFL players, including people who played just a single game in the league, who died between 2008 and 2021. The researchers zeroed in on deaths that occurred in the latter six years when brain donation, often by players’ family members, was most frequent.
From 2016 to 2021, 878 former players died. Of those players, 235 donated their brains and 215 of those brains were found to have CTE, according to results published in The BMJ, a peer-reviewed journal.
That’s how the study concluded that at least 25 percent of the NFL players who died had CTE. The researchers noted, however, that the actual rate of CTE among former players is likely higher since there were probably cases of the disease in the 643 athletes whose brains weren’t donated.
The study also found that about 60 percent of people with CTE had dementia and exhibited severe signs of impairment, including not being able to feed or groom themselves.
“It shows that this pathology obviously isn’t something benign in the brain,” Daneshvar said.
He called for a “substantial investment” in treatments and cures. There are ways to treat symptoms of the disease, but no interventions that target the underlying process.
In the meantime, the new findings should prompt greater efforts across all levels of the sport to reduce the number of head injuries, experts said.
CTE, Daneshvar said, is not linked to just a handful of concussions. Risk is associated with the cumulative impact load a person’s brain experiences over years or decades — more on the order of thousands of hits.
Youth, high school, and collegiate football programs should follow NFL protocols on full-contact practices, which limits them to once a week, said Daneshvar, whose own son is playing flag football in the fall.
“If we did that at all of those other levels of play, we would reduce the number of head impacts by well over 60 percent and that would result in substantially reduced rates of neurodegenerative diseases later in life,” he said.
High school football programs take the risks of head trauma seriously, said Milton High head coach Steve Dembowski, the coaching representative for the Massachusetts Interscholastic Athletic Association’s football committee. “We don’t tackle ‘live’ [in practice] all year.”
Some teams, he added, use “thud” tackling — the drill stops after an initial collision, instead of players bringing each other to the ground.
But on-the-ground reports at local practices reveal that guidelines are not always followed everywhere.
At all levels, some players are also turning to newer equipment technology, such as safety caps that go over helmets and are designed to absorb impact.
Erin Hanson, CEO of Guardian Sports, which makes a safety cap, said the latest study reinforces the understanding that players must reduce the impacts of all head injuries, not just concussions, they might experience over the course of their careers.
But equipment, Hanson said, is “one piece, and it is not the largest one.”
“No helmet or piece of equipment prevents or treats CTE, and we have never claimed one does,” Hanson said.
The NFL mandates every player — save for rarely-tackled quarterbacks, kickers and punters — wear the padded helmet coverings during practices with body contact.
Starting in 2024, players had the option to wear them in games, but few do. Two Patriots — offensive lineman Jared Wilson and wide receiver Romeo Doubs — are among them.
“You can get ankle replacements, shoulder replacements, knee replacements,” Wilson told the Globe in February, adding: “You can’t replace your brain.”
The MIAA considers soft-shell helmet coverings to be optional for games and practices. Dembowski, the Milton High coach, rattled off several recent opponents that scrimmaged against his team in protective caps: Weston, Westwood, Xaverian, Wellesley, and Swampscott.
Sharon High, which has since merged with Dedham to form a cooperative team, wore the protective caps in games last season following the catastrophic brain injury sophomore Rohan Shukla suffered in a November 2024 game.
Ben Volin and Nicole Yang of the Globe Staff contributed reporting.