New Study Estimates About 75% of Recently Deceased NFL Players Had CTE, and Experts Urge Caution

A new study estimating that nearly 75% of NFL players who died over a 15-year period had signs of chronic traumatic encephalopathy, or CTE, in their brains is drawing attention. Experts say the finding underscores the need to gather more data on the condition.

CTE is found in people who have taken repeated blows to the head and can be definitively diagnosed only after death. It has also been identified in first responders and military members, but it is rarely seen in the general population.

The Boston University research, published in JAMA Network Open, builds on data released in The British Medical Journal in August. That earlier work put the share of ex-NFL players who died between 2016 and 2021 and had CTE as high as 98%. The broad estimate reflected uncertainty over how representative the studied brain donors were of all NFL players, since donors are more likely to have symptoms believed to be linked to CTE.

The Boston team examined brains donated by 387 players who died between 2008 and 2023. They were a subset of the 2,362 former NFL players who died in that span. Ninety-four percent of the donors had some form of CTE. The researchers estimated that former players with cognitive symptoms were five times more likely to have their brains donated than others, and from that they calculated that 74.5% of players had some form of CTE.

CBS News chief medical correspondent Dr. Jon LaPook cautioned that the figure may be an overestimate. He noted that the study measured how many former players showed signs of CTE in the brain, not how many had actual symptoms.

Dr. Kristen Dams-O'Connor, director of the Brain Injury Research Center at Mount Sinai, said the results "cannot and should not be interpreted as being representative of current living athletes." She noted that many of those studied ended their careers long ago. The NFL has since changed rules to reduce concussions and introduced more protective equipment, which she said "should translate to lower CTE risk in recent generations of players." The league told CBS News it "continuously strives to make the game of football safer." Dams-O'Connor added that Boston University used "strong methods" to adjust for selection bias, but gaps remain, including the roughly 20,000 NFL players who could have died in the period but did not. The results also cannot be applied to most people who played youth football or other non-professional contact sports.

Dr. Jeremy Tanner of the UT San Antonio Health Science Center called it a helpful study. "Even taking that selection bias into account, when you look more broadly, it's at a minimum 20 to 25%, which is eye-opening and really shows the need to both advance the research," he said.

Dr. Jay Alberts, director of the Cleveland Clinic Concussion Center, said the data shows the need to look for early warning signs. Rather than a truly silent phase, he said, "I think what we need to do is listen more carefully and use better measurements." He pointed to instrumental activities of daily living, such as driving or balancing a checkbook, which draw on cognitive and motor function at once. In Alzheimer's and Parkinson's disease, these begin changing five to seven years before diagnosis, and CTE may follow a similar pattern. Better early detection could lead to interventions that might "slow it or even potentially reverse it."

Alberts and Tanner also highlighted research into biomarkers possibly tied to CTE. Ongoing studies, including one with a site at UT Health San Antonio, follow current or former players over their lifetimes. Alberts called for more long-term research, and Tanner said such work can benefit more than just former NFL players. He expressed hope that tools and biomarkers will one day detect these brain changes during life, allowing researchers to "learn ways to better prevent or treat these diseases."