An analysis of the medical records of more than 2,000 deceased former NFL players estimates that a staggering 74.5% of them likely had chronic traumatic encephalopathy, a neurodegenerative brain disease tied to high-impact sports such as football.
Boston University has been on the forefront of diagnosing CTE for years and spearheaded the newstudy. Yet because the brain disease currently can be diagnosed only after death, conclusions from previous studies were marred by selection bias — a systematic error that occurs when those chosen for analysis do not properly represent the target population.
Eliminating selection bias was the impetus for the study published Wednesday in the medical journal JAMA Network Open that combined data from 2,362 players who died from 2008 to 2023. The total included 396 players who donated their brains and National Death Index records of 1,966 deceased players who didn’t. Nearly 94% of the donated brains had CTE.
The 74.5% estimated prevalence was concerning and efforts to diagnose CTE during life must continue, said Julia Gallini, lead author of the study conducted by Mass General Brigham and the Concussion & CTE Foundation in addition to Boston University, in a statement.
“More than 20 million American men alive today have played football,” Gallini told MedicalResearch.com. “It is crucial to learn how many may have CTE to ensure the medical community is prepared to support families fighting suspected CTE.”
The new analysis is the first comprehensive effort by scientists to understand the prevalence of CTE among deceased former NFL players, according to the study. The focus was to minimize selection bias, Gallini said, as earlier studies showed that players with cognitive symptoms while they were alive were about five times more likely to have their brain donated than players without cognitive symptoms.
“We used this estimate to scale down the 94% CTE prevalence in our brain bank to a 74.5% CTE prevalence among all deceased former NFL players,” said Gallini, a Boston University PhD candidate in Biostatistics.
A study by Boston University two months ago examined whether severe CTE was linked to cognitive decline. Among all NFL brain donors, nearly 60% had dementia and 90.4% of those with the most severe form of CTE — Stage IV — had dementia.
“No other environmental or occupational exposure ever studied is known to have increased dementia risk at death by that amount,” said Yorghos Tripodis, senior author of the paper and a professor of biostatistics at Boston University.
Brain donors in the study were more likely than non-donors to be white, to have died younger and to have played longer in the NFL.
“Even after accounting for differential brain donation, our findings suggest that the prevalence of CTE among deceased NFL players remains high,” the study said.
The August study published in the British Medical Journal estimated that one in four former NFL players who died between 2016 and 2021 had CTE. Of the 878 players who appeared in at least one NFL game and died in that six-year period, at least 25% had CTE.
However, Dr. Daniel Daneshvar, the study’s lead author, said 25% was an estimate on the “low end.” The study found that the maximum possible prevalence of CTE was about 97%, and that the true rate “is somewhere in the middle,” Daneshvar said.
The NFL “continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts. We encourage former players to utilize these resources to identify and seek treatment when they are concerned about their health,” the organization said in a statement.
The NFL Players Association said Wednesday that such studies “are critical to improving our understanding of football’s long-term impacts.” The union had more to say after the August study: “This is a sobering reminder that football carries real risks, and those risks can have lasting consequences for players and their families. It also reinforces one of the NFLPA’s core priorities: improving player safety and supporting players throughout their lives, both during and after their careers.”
The prevalence of CTE in college, high school and youth tackle football players is a growing concern even though data is sparse because the disease can’t be detected until death.
CTE might also be an issue with NASCAR drivers. Boston University diagnosed Hall of Fame driver Fred Lorenzen with Stage 3 CTE after he died in December at 89. Lorenzen, who lived with dementia for 20 years, is the first confirmed NASCAR driver diagnosed with the disease.
“We are making significant progress towards diagnosing CTE in living patients, which will allow us to start clinical trials to find treatments and ultimately a cure,” Gallini said. “We invite former players to enroll in studies aimed at diagnosing and treating CTE during life. We hope this informs conversations on CTE prevention.
“This disease is preventable,” Gallini continued. “Repeated head impacts are the only known risk factor, so we need to limit the number of times players are hit in the head.”
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