Study Finds 75% of Deceased NFL Players Had CTE

A new analysis suggests that chronic traumatic encephalopathy was present in the brains of an estimated 75% of professional football players who died over a 15-year period. The study, published in JAMA Network Open on Wednesday, presents the highest prevalence rate for the disease recorded to date. This figure is three times higher than a previous estimate from the same research group, which found that about 25% of players who died over a five-year span showed signs of CTE.

Yorghos Tripodis, director of statistics and data management at the Boston University Alzheimer's Disease and CTE Center, led the research. He noted that the high percentage was unexpected. "I had to double-check the numbers," Tripodis said. He explained that the figure is an estimate because CTE cannot currently be diagnosed while a person is alive. The center manages the UNITE Brain Bank, which examines donated brains for damage caused by repetitive head trauma.

Diagnosing CTE is difficult because the microscopic changes in the brain do not show up on standard scans. The condition can only be confirmed through autopsy. Previous studies have faced criticism for selection bias, as families of players with cognitive decline are more likely to donate brains. An earlier Boston University study found CTE signs in 99% of donated brains from former NFL players, a rate that likely overstates the disease's true prevalence among all deceased players.

To account for this bias, Tripodis and his colleagues combined data from 396 donated brains with national death records for 1,966 other former NFL players who died between 2008 and 2023. They analyzed factors including age at death and estimated rates of mild cognitive impairment and dementia in players over 50. The team determined that families of symptomatic players were about five times more likely to donate brains. After adjusting for this disparity, they calculated that approximately 1,760 of the roughly 2,360 players who died during the study period had CTE.

About 93% of the donated brains examined showed signs of the disease. For context, the researchers noted that only about 1% of brains donated to banks in the U.S., Austria, and Brazil show signs of CTE. The study also estimated that about 27% of the deceased players had dementia. However, not everyone with CTE develops cognitive decline, and some individuals never experience symptoms.

Dr. Jim Kelly, a professor emeritus of neurology at the University of Colorado Anschutz, urged caution regarding the findings. He was not involved in the research. Kelly pointed out that the study relied on autopsies for a small fraction of the deceased players. "They had no autopsies on five times as many players who died as they did have autopsies for," he said. He also noted that some autopsies may have revealed only minor lesions, which might not lead to behavioral changes or dementia.

Dr. Julian Bailes, chair of neurosurgery at Endeavor Health in the Chicago area, explained that repeated head impacts cause tau proteins to build up in the brain. This accumulation 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 stated that reducing the number of brain injuries is the primary method for lowering risk. In an emailed statement, an NFL spokesperson said the league continuously strives to make the game safer. The league has introduced measures such as redesigned helmets and the dynamic kickoff rule, which lowers collision speeds.