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. 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 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.
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