New Analysis Finds CTE Signs in 75% of Deceased NFL Players

Researchers at Boston University estimate that 74.5% of former NFL players who died between 2008 and 2023 had signs of chronic traumatic encephalopathy in their brains. The new figures come from a study published in JAMA Network Open. The team examined brain tissue from 387 deceased players. These individuals represented a subset of the 2,362 former players who died during that 15-year period. Ninety-four percent of the analyzed brains showed some form of CTE.

The study builds on earlier data released in The British Medical Journal in August of this year. That previous work suggested the share of former players with CTE could be as high as 98%. The higher initial estimate reflected uncertainty about how representative the brain donors were of the entire player population. Donors are more likely to have donated tissue if they suffered from cognitive symptoms linked to the condition.

To account for this selection bias, the Boston team calculated that former players with cognitive symptoms were five times more likely to have their brains donated. By adjusting for that factor, the researchers arrived at the 74.5% figure. CTE is a degenerative condition found in people who have taken repeated blows to the head. It can only be definitively diagnosed after death. While it has been identified in first responders and military members, it is rarely seen in the general population.

Experts are urging caution in how the new numbers are interpreted. Dr. Jon LaPook, chief medical correspondent for CBS News, noted that the study measured signs of CTE in the brain rather than actual symptoms experienced by the players. He suggested the figure may be an overestimate. Dr. Kristen Dams-O'Connor, director of the Brain Injury Research Center at Mount Sinai, emphasized that the results cannot be interpreted as representative of current living athletes. Many of the players studied ended their careers decades ago.

The NFL has changed its rules in recent years to reduce concussions. The league has also introduced more protective equipment. Dams-O'Connor said these changes should translate to a lower CTE risk for recent generations of players. The league told CBS News that it continuously strives to make the game of football safer. Dams-O'Connor acknowledged that Boston University used strong methods to adjust for selection bias. She noted that gaps remain, including the roughly 20,000 NFL players who could have died in the period but did not.

Dr. Jeremy Tanner of the UT San Antonio Health Science Center called the study helpful. He stated that even accounting for selection bias, the rate is at a minimum of 20 to 25%. He described that number as eye-opening and a clear signal of the need to advance research. The results also cannot be applied to most people who played youth football or other non-professional contact sports.

Dr. Jay Alberts, director of the Cleveland Clinic Concussion Center, said the data shows the need to look for early warning signs. He argued that researchers should listen more carefully and use better measurements. He pointed to instrumental activities of daily living, such as driving or balancing a checkbook. These tasks draw on cognitive and motor function at once. In Alzheimer's and Parkinson's disease, these abilities begin changing five to seven years before diagnosis. Alberts suggested CTE may follow a similar pattern.

Better early detection could lead to interventions that might slow or even potentially reverse the condition. Alberts and Tanner both highlighted ongoing research into biomarkers possibly tied to CTE. 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. 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.