Three in Four Former NFL Players Who Died From 2008 Through 2023

The researchers also estimate that around one in four of the former football players had dementia, a common feature of late-stage CTE. Researchers say that CTE is very preventable, since less than 1 percent of brains from the general public show signs of it. Scott Taetsch via Getty Images American football is famously a dangerous sport.

In August, a study found that at least one in four recently deceased former NFL players had a brain disease called chronic traumatic encephalopathy, or CTE, forcing a conversation around safety in the sport. The actual image might be even starker. New work by some of the same researchers suggests that three in four of the retired professional athletes who died from 2008 through 2023 likely had CTE.

The findings were published in the journal JAMA Network Open on October 28. “More than 20 million men alive today in the U.S. Have played football, so understanding how many of them have CTE is an important public health question,” says study co-author Yorghos Tripodis, a biostatistician at Boston University, to Youri Benadjaoud and Betsy-Ann Assoumou at ABC News.

CTE is a progressive brain disease likely caused by repeated head injuries. Symptoms are thought to include mood swings, memory loss, depression and dementia, but CTE can only be diagnosed after death. That’s because one definitive sign is the buildup of the protein tau, also implicated in Alzheimer’s disease, which causes the brain to atrophy.

The autopsy-dependent diagnosis has long skewed CTE research, given that families are more likely to donate brains of former athletes who showed symptoms of the disease. Tripodis and colleagues tried to adjust for selection bias.

They analyzed the medical records of 2,362 former NFL players—in the league for an average of five years—who died between January 2008 and December 2023. Most of them were not brain donors.

But by looking for documentation of dementia or other cognitive issues, the scientists found that those showing potential behavioral signs of CTE were around five times more likely to have their brains donated for research. Then, the researchers found that out of 387 brain donors, nearly 94 percent had CTE.

Adjusting that percentage for the donation bias yielded the estimate that 74.5 percent of former NFL players in the cohort died with CTE. For comparison, less than 1 percent of brains from members of the general population in research banks show signs of CTE, Tripodis tells Jackie Flynn Mogensen at Scientific American.

What’s more, roughly one in four ex-football players had dementia, the team calculates, a figure that is likely an underestimate. CTE and football CTE was first diagnosed in a former NFL player in 2005.

The league didn’t acknowledge an association between the sport and the progressive brain disease until 2016. Zachary Binney, an epidemiologist at Emory University who wasn’t involved in the study, tells Carolyn Y.

Johnson and John Branch at the New York Times that the research was “pretty rigorous, and the methods seem reasonable and valid.” “It is higher than I would have guessed previously,” he adds. “But this paper has a larger data set and applies stronger methods than previous work.” When asked about the findings, the NFL pointed to its response to the August study, report Diana Anos and Nadia Kounang at CNN.

“The NFL continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts,” the organization said. Julie Stamm, a neuroscientist at the University of Wisconsin-Madison, tells CNN that the NFL could do more to protect players, such as banning tackles during practice.

“If the NFL says that, the youth levels, the younger levels, they’ll listen, and that will go a long way in decreasing the overall number of impacts over a lifetime that these individuals sustain, which is what we’ve seen increases the risk for CTE,” says Stamm, who wasn’t involved in the study. Still, studying CTE remains difficult.

Researchers can’t know how many living football players are walking around with the undiagnosed brain disease.

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