A recent study found that roughly 75% of deceased NFL players had at least some case of CTE.
Chronic traumatic encephalopathy (CTE) is a progressive, degenerative brain disease linked to repeated head impacts rather than a single injury, according to the Mayo Clinic.
The study from Boston University researchers consisted of more than 2,300 deceased former players aged 80 or older who died between 2008 and 2023, nearly 400 of whom were donors.
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Out of the 396 who donated their brains to research, 93.5% of them were diagnosed. Researchers estimated that former NFL players with clear cognitive symptoms were roughly five times more likely to donate their brains than those without such symptoms.
Donors also died younger on average – 67 years old compared to almost 75.
CTE can only be diagnosed after death and is identified in four stages, with stage 4 being the worst.
“Many cases may have been early stage at the time of death and possibly symptom free,” the study noted.
The study also estimated that 27.2% of the players had a history of all-cause dementia during life, but it did not conclude whether dementia was caused by CTE.
A study released in August found that at least 1 in 4 people who have played in the NFL might expect to end up with CTE at some point in their lives.
The symptoms found in those with CTE include memory loss, mood swings, erratic behavioral actions and more.
While the disease was first found in boxers, it has become associated with football players in this modern era due to the repeated blows to the head sustained on every snap of the ball. It has, however, also been found in athletes participating in hockey, rugby and other sports.
But its connection to football became public when beloved players like Junior Seau, Mike Webster, Frank Gifford and others were diagnosed with CTE after their deaths. Webster was dubbed “Patient Zero” after Dr. Bennet Omalu examined his brain and became the first to diagnose an NFL player with CTE, jump-starting a concussion crisis within the game.
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There were 168 documented in-game concussions during the 2025 NFL season, which was a 30% increase from the 129 recorded during the 2024 campaign. There were a total of 538 evaluations and 26 medical timeouts as well.
OutKick’s Scott Thompson contributed to this report.