Boston University Research: 75% of Deceased Ex-NFL Players Showed CTE Signs

An estimated 75% of professional football players who died between 2008 and 2023 had signs of chronic traumatic encephalopathy, according to a study published in JAMA Network Open on Wednesday. The finding marks the highest estimate to date, tripling the figure from a study released in August by the same research group, which placed the rate at 25% for a five-year period.

The study, led by Yorghos Tripodis, director of statistics and data management at the Boston University Alzheimer’s Disease and CTE Center, analyzed data from 396 donated brains and records for 1,966 other deceased former NFL players. Tripodis said the team had to double-check the numbers because the results were surprising, though he noted the figure remains a best guess due to the lack of a definitive diagnosis for living patients.

Previous research has faced criticism for selection bias, as families of players with cognitive symptoms are more likely to donate brains for study. A prior analysis found that 99% of donated brains from former NFL players showed CTE signs. To correct for this, the new study factored in that families of players with symptoms were about five times more likely to donate brains. After adjusting for this bias and accounting for the ages at death, the researchers estimated that roughly 1,760 of the 2,360 former players in the dataset had the condition.

While 75% of the deceased players showed structural damage associated with CTE, the study estimated that only about 27% had dementia. Tripodis stated that while dementia can stem from various causes, it is very likely that CTE is the driver in this specific population. Dr. Julian Bailes, chair of neurosurgery at Endeavor Health, explained that repeated head impacts cause proteins called tau to build up in the brain, leading to damage in areas that regulate behavior and emotion.

Dr. Jim Kelly, a professor emeritus of neurology at the University of Colorado Anschutz, noted that because the condition is currently diagnosable only through autopsy, these numbers remain estimates. He observed that some autopsies reveal few lesions, which may not lead to behavioral changes or dementia. Bailes agreed that the findings call for more research into diagnosing CTE in living patients, stating that it is difficult to help those with the disease if it is only identified after death.

The NFL responded to the findings in an emailed statement, saying the league continues to strive to make the game safer by implementing strategies to reduce concussions and head impacts. These measures include redesigned helmets, such as the Guardian Cap, and the dynamic kickoff rule, which lowers collision speeds. Tripodis emphasized that reducing the number of brain injuries and impacts substantially decreases the risk of developing the condition.