Nearly three out of four former NFL players who died over a 15-year span had chronic traumatic encephalopathy, according to research published Wednesday in the medical journal JAMA Network Open. The findings represent the highest population-level estimate to date for the degenerative brain disease among former professional football competitors.
Led by researchers at Boston University, the analysis evaluated records from 2,362 former players who died between 2008 and 2023. The authors calculated that an estimated 74.5 percent of those deceased athletes had the condition, which has been linked to repetitive impacts to the head.
Correcting for donation bias
Past inquiries into the disease faced significant statistical hurdles because CTE can only be diagnosed posthumously through an autopsy. Families of athletes who exhibited mood swings, memory loss or other behavioral symptoms were far more inclined to submit tissue for research, skewing previous raw datasets. In the examined group, 396 players had donated their brains to the Understanding Neurologic Injury and Traumatic Encephalopathy Brain Bank, and 93.5 percent of those donated samples showed signs of CTE.
To produce a more representative figure for all 2,362 deceased players, the team adjusted for this selection disparity. The researchers determined that relatives who observed cognitive problems were roughly five times more likely to donate a brain. After applying statistical corrections to account for the remaining 1,966 players who were not autopsied, the calculated rate settled near 75 percent.
“No study like this can remove every possible bias. But even under very conservative assumptions, the estimate does not go below 60%,” senior author Yorghos Tripodis, a biostatistics professor at Boston University, told ABC News. Even the team’s lowest conservative modeling placed the rate at 63.7 percent, Yahoo Sports reported.
By comparison, researchers noted that fewer than one percent of brain tissue samples collected from community banks in the general population display markers of the disease.
Symptoms and dementia risks
CTE involves an accumulation of abnormal tau proteins that damage neural tissue and cause cell death over time. However, the presence of these structural changes does not necessarily guarantee that an individual will develop clinical symptoms during life, experts said.
The study estimated that 27.2 percent of the deceased athletes suffered from dementia during their lifetimes. While that neurological decline can stem from multiple causes, Tripodis told NBC News that CTE was very likely the underlying driver within this specific group.
Outside neurologists emphasized that any population-wide calculation remains an estimation until physicians discover reliable tools to detect the illness in living patients. Dr. Julian Bailes, neurosurgery chair at Endeavor Health, told NBC News that microscopic tau changes do not appear on standard clinical scans, complicating diagnosis and patient care during retirement.
The league’s response
In response to the publication, the NFL Players Association called such studies essential to understanding football’s long-term physical toll. The union stated it “remains committed to supporting scientific research, investing in resources that aid players’ physical and mental well-being, and expanding access to care.”
The NFL reiterated that it works continuously to minimize head impacts. In an emailed statement cited by NBC News, a league spokesperson said the organization “strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts.” In recent years, the league has introduced revised kickoff formats and approved padded helmet coverings known as Guardian Caps.
Scientists say the next major hurdle will be discovering biomarkers that allow clinicians to diagnose CTE in living patients, opening the door to early medical interventions before severe cognitive decline takes hold.
