Study Estimates 75% of Deceased Former NFL Players Had CTE, Experts Urge Caution
Boston University researchers found signs of the brain disease in 94% of 387 donated brains, then adjusted for who donates. Outside doctors say the figure shouldn't be applied to today's players.
A new study from Boston University estimates that about three in four former NFL players who died in recent years had chronic traumatic encephalopathy, the degenerative brain disease tied to repeated blows to the head, though doctors outside the research team warn the number should not be read as a measure of risk for athletes playing today.
The study, published in JAMA Network Open, examined brains donated by 387 former NFL players who died between 2008 and 2023. They were a subset of the 2,362 former players who died in that period. Ninety-four percent of the donated brains showed some form of CTE. The researchers then adjusted for the likelihood that brain donations skew toward players who had symptoms, estimating that players with cognitive symptoms were five times more likely to donate. After that correction, they put the share of all former players who died in the window with CTE at 74.5%, which is nearly 75%.
CTE can only be definitively diagnosed after death. It has also been found in other athletes, first responders and military members, but is rarely seen in the general population. The new estimate follows a study published in The British Medical Journal in August that put the share of ex-NFL players who died between 2016 and 2021 with CTE somewhere between 25% and 98%, a range that reflected uncertainty over how representative brain donors are.
CBS News chief medical correspondent Dr. Jon LaPook said the 75% figure may be an overestimate, noting the study measured signs of CTE in the brain, not actual symptoms in life. 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 said Boston University used "strong methods" to address selection bias but gaps remain, including about 20,000 NFL players who could have died during the period but did not appear in the data, and that the findings do not apply to youth football or other non-professional contact sports. She expects recent players to have lower CTE risk because of rule changes and better protective equipment.
Dr. Jeremy Tanner of UT Health San Antonio called the work helpful for seeing the bigger picture. Even accounting for selection bias, he said, the true share is "at a minimum 20 to 25%," a figure he called eye-opening.
Dr. Jay Alberts of the Cleveland Clinic Concussion Center said the findings show doctors need to look for early warning signs. He argued CTE may have a "silent phase" that is not truly silent, and said better measurements are needed. He suggested tracking everyday tasks such as driving or balancing a checkbook, which in Alzheimer's and Parkinson's begin changing five to seven years before diagnosis.
The NFL told CBS News it "continuously strives to make the game of football safer," including by reducing concussions and head impacts. With no test that can diagnose CTE in a living person, the central question for players, families and the league remains how to spot the disease early enough to matter.
