1 in 4 former NFL players who died from 2016 to 2021 had CTE, study estimates

By Nadia Kounang, CNN

(CNN) — At least 1 in 4 former National Football League players who died between 2016 and 2021 had chronic traumatic encephalopathy, according to a new study.

The study, released Tuesday in the journal BMJ, is “one of the most informative estimates to date of CTE burden among former NFL players,” according to an editorial published with it.

CTE is a neurodegenerative disease associated with repeated blows to the head. It can be diagnosed only after death, although symptoms may include memory loss, impulse control problems, anxiety, depression and anger issues. It’s most often seen in people who play contact sports such as football, hockey and soccer, but it has also been detected in the brains of troops who have been injured in explosions and in some people who experience domestic violence. In the brain, it is marked by an abnormal buildup of the protein tau.

A separate recent analysis detected the disease in 99% of former NFL players who had donated their brains for research. However, a significant limitation of that study was in its potential bias: It was done in a group of people whose brains had been donated by family members who may have noticed symptoms while the person was still alive.

For the new study, researchers from Mass General Brigham, Boston University and the Concussion & CTE Foundation — many of whom had been involved in the previous CTE research — set to overcome that limitation by analyzing the total number of NFL deaths between 2008 and 2021.

The researchers compared data from death certificates against the number of brain donors with confirmed CTE. They further narrowed the time period to between 2016 and 2021, when the highest number of brain donations had been received.

Of 878 former players who died in that time frame, 235 had donated their brains for research. Among those, 215 had been diagnosed with CTE. Many of the donations had been analyzed at brain banks at Boston University and the University of California, San Francisco.

An NFL spokesperson said Tuesday that the league “continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts.”

“The NFL remains ​committed to ensuring that the NFL community has access to a robust – and expanding – set of resources ​to enhance their physical and mental well being. We encourage former players to utilize these ⁠resources to identify and seek treatment when they are concerned about their health.”

The study’s lead author, Dr. Daniel Daneshvar, chair of physical medicine and rehabilitation at Mass General Brigham and an associate professor at Harvard Medical School, said that repeated traumatic brain injuries are a known factor in elevated rates of neurodegenerative disease.

“Similarly, we and others have shown that in NFL players, specifically, there is about a four times higher rate of death from neurodegenerative disease than the general population,” he added.

The ​study also found that dementia was common among ​the brain donors, with the researchers urging prevention measures focused on cutting down on repetitive head impacts across all levels of the sport.

“The ‌bulk ⁠of the head impacts that these former NFL players experienced didn’t occur at the NFL level. They occurred at the collegiate level … and at the high school level and in many cases the youth level. And all of those cumulative hits to the head added up to result in an increased risk,” Daneshvar said.

Dr. Rachel Grashow, director of research initiatives for the Football Players Health Study at Harvard University, said the new study is “important,” but she also noted that a diagnosis of CTE didn’t always correlate with symptoms. CTE is diagnosed in four stages based on location and accumulation of the protein tau.

“The scientific community looks at this paper and says, ‘OK, now we’ve got a denominator. We know who’s got these proteins. We know who doesn’t. That’s helpful.’ The worry is that the rest of the world will see this … number and say ‘that’s symptoms,’ ” said Grashow, who was not involved in the new research.

For current players, she said, the real question for scientists involves trying to delineate who had symptoms and why, teasing out whether those symptoms were happening because of CTE or were only amplified by it.

“Head injury is absolutely bad for you, and it causes low testosterone, it causes sleep apnea, it causes depression, it causes high blood pressure, causes tinnitus. It causes a lot of things that are bad for you, and those things, if left untreated, are really bad for your brain. And we don’t know how much tau accumulates or how that synergizes with brain injury. This is a big question mark.”

The NFL’s 2011 Collective Bargaining ​Agreement limited the number ​of contact practices during the ⁠season. The current CBA was ratified in 2020 and runs through March 2031. The Ivy League banned full-contact tackling during practices five years later.

The US Supreme Court cleared the way for the NFL’s settlement of concussion-related lawsuits with thousands of retired ​players in 2016.

“If the changes that have been implemented at the NFL level, including reducing ​the amount of ⁠contact in sports practices to less than one per week, were propagated at the collegiate, high school and youth levels, athletes would be better off,” said Daneshvar, who urged current and former athletes who notice cognitive symptoms to get checked out by a neurodegenerative ⁠disease ​expert.

“We know that nearly 70% of head impacts are occurring in ​practice. So without changing a single minute of game time at any of those levels, we can be substantially reducing the cumulative head impact ​burden that these individuals are experiencing throughout their lives.”

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Jill Martin and Reuters contributed to this report.