A large-scale new study is raising fresh concern about the long-term brain risks of pro football after scientists discovered that at least one in four retired NFL players who died in a large, population-based study had a form of brain damage called chronic traumatic encephalopathy, or CTE. The results offer one of the most definitive estimates yet of the brain disease’s prevalence among pro players who have died.
In a separate study, Boston University, Mass General Brigham and the Concussion & CTE Foundation researchers examined the brains of 1,712 former NFL players who had died from 2008 through 2021. They focused on the players who had died from 2016 to 2021, and of those, 215 of 235, or 93.2%, had CTE pathology. Brain donors are not representative of all players, so the researchers used statistical modeling to estimate prevalence of CTE.
Adopting the most generous possible assumption that none of the players with unexplored brains had CTE they arrived at a minimum prevalence of 24.5%. At the most severe end of the spectrum, that number jumps to 97.7%. The authors note that this latter number is a “mathematical maximum, ” not an estimate of the true rate.
That is crucial because right now CTE can only be definitively diagnosed post-mortem through an autopsy. The researchers have yet to identify a test to find the disease in a living individual. As a result, they cannot just scan all current NFL players, and check how many have the disease. So, the researchers are reporting the pathology of CTE in former NFL players who have died rather than the frequency of CTE in current or retired players.
What is CTE? CTE is a neurodegenerative disease related to repeated hits to the head. Researchers have identified the disease with abnormal tau protein buildup in various parts of the brain. Researchers and physicians also believe the increased risk of CTE is related to a person’s total amount of repeated head hits, even hits that do not result in a diagnosed concussion.
There was also something striking about the severity of the disease. Approximately 70% of the players whose brains showed CTE were found to have Stage 3 or Stage 4, the two most severe forms of the disease out of four. Over 60% of players with CTE were determined to have had dementia based on medical records and family interviews. Among players with Stage 4 CTE, more than 90% had dementia.
The results come on the heels of other research showing increased risk of neurological disease among professional footballers. An earlier 2026 analysis of almost 20,000 former NFL players indicated that they were around four times more likely to die from a neurodegenerative disorder than the general population. That study also found increased death rates due to ALS and other conditions.
But scientists are quick to point out that the new CTE study has some significant flaws. Individuals who donate their brains for research are more likely to have had behavioral or neurological symptoms and the donated players had tended to have longer playing careers and more high-profile careers than some other football players.
