New Study Finds 75% of Deceased NFL Players Had CTE

An estimated 75% of former National Football League players who died between 2008 and 2023 had chronic traumatic encephalopathy, according to a study published in JAMA Network Open on Wednesday. This figure represents the highest estimate to date for the prevalence of the condition among deceased professionals.

The research team examined data from 1,966 deceased players and 396 donated brains. They calculated that approximately 1,760 of the 2,360 players who died during the 15-year period likely had CTE. The study also estimated that 27% of the group suffered from dementia. Researchers noted that the new 75% figure is three times higher than a previous estimate from August, which placed the rate at 25% for a five-year span.

Yorghos Tripodis, director of statistics and data management at the Boston University Alzheimer's Disease and CTE Center, led the study. He stated that the high percentage was unexpected. “I had to double-check the numbers,” Tripodis said. He explained that the figures are estimates because CTE cannot currently be diagnosed in living patients. “Right now we don't know how to diagnose CTE when people are alive, so we are trying to estimate,” he added.

The methodology aimed to correct for a known bias in brain donation. Families of players with cognitive symptoms were roughly five times more likely to donate brains than those without symptoms. The team used statistical analysis to account for this disparity, comparing donated brain tissue with national death records. They found that 93% of the examined donated brains showed signs of CTE, compared to about 1% of brains in donation banks across the U.S., Austria, and Brazil.

Experts outside the study urged caution regarding the results. Dr. Jim Kelly, a professor emeritus of neurology at the University of Colorado Anschutz, noted that the researchers lacked autopsies for five times as many players as they had available. He suggested that some autopsies might have shown only minor lesions, which may not cause behavior changes or dementia.

Dr. Julian Bailes, chair of neurosurgery at Endeavor Health, explained that repeated head impacts cause tau proteins to accumulate in the brain. This buildup can affect areas regulating behavior and emotions, leading to memory loss, depression, and mood swings. Bailes emphasized the need for better diagnostic tools for living patients. “If you can't tell if someone has a certain disease until they're dead, you really can't help them,” he said.

Tripodis stressed that reducing the frequency of brain injuries is the primary path to lowering risk. An NFL spokesperson responded in an emailed 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 the Guardian Cap and a dynamic kickoff rule designed to lower collision speeds.