Study puts CTE rate in deceased former NFL players at 75%
Boston University researchers adjusted for donation bias to estimate that nearly three-quarters of players who died between 2008 and 2023 had signs of the disease.
By Samir Patterson ·
The prevalence of chronic traumatic encephalopathy in former professional football players is substantially higher than previous estimates suggested.
A study published in JAMA Network Open on Wednesday found that approximately 75% of former NFL players who died between 2008 and 2023 showed signs of CTE in their brains.
This figure represents the highest estimate to date. In August, the same research group reported that one-quarter of deceased NFL players had CTE based on a five-year dataset. The new analysis tripled that percentage.
Yorghos Tripodis, director of statistics and data management at the Boston University Alzheimer’s Disease and CTE Center, said the results were unexpected. "I had to double-check the numbers," he said. "Right now we don't know how to diagnose CTE when people are alive, so we are trying to estimate."
The study team combined data from 396 donated brains with national death records for 1,966 other deceased former NFL players. They used this data to create a statistical model that accounts for the fact that families of players with cognitive symptoms are more likely to donate brains.
A previous Boston University study found that 99% of brains donated by former NFL players had CTE. Tripodis and his team determined that families of players with symptoms were five times more likely to donate brains than families of those without symptoms. The new model corrects for this selection bias.
The researchers estimated that about 1,760 of the roughly 2,360 former players who died during the 15-year period had CTE. They also estimated that 27% of these players had dementia. Tripodis noted that while dementia can stem from various causes, CTE is a likely driver in this specific population.
Dr. Julian Bailes, chair of the neurosurgery department at Endeavor Health, explained that repetitive head impacts cause proteins called tau to build up in the brain. This accumulation leads to structural damage that is only visible during an autopsy. "If that happens over and over again, that damage accrues," Bailes said.
The NFL released a statement saying the league "continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts." The league has introduced redesigned helmets and the dynamic kickoff rule to lower collision speeds.
Dr. Jim Kelly, a professor emeritus of neurology at the University of Colorado Anschutz, noted that the study relies on estimates because the condition cannot be diagnosed in living patients. "These are all estimates. They had no autopsies on five times as many players who died as they did have autopsies for," Kelly said. Tripodis emphasized that reducing the number of brain impacts remains the primary way to lower the risk.
