Study estimates CTE in three-quarters of deceased former NFL players

Nearly three-quarters of former NFL players who died from 2008 through 2023 had signs of CTE, according to a Boston University-led study published Wednesday in JAMA Network Open.

The researchers estimated a 74.5% prevalence of chronic traumatic encephalopathy among deceased former players, using records from about 2,362 people. It is the first population-level estimate aimed at getting beyond a long-running problem in CTE research: the brains available for study are not a random sample of football players.

The catch: Families of former players with cognitive or CTE-related symptoms were estimated to be about five times more likely to donate a relative's brain for research than families of players without those symptoms. Among the nearly 400 donated brains in this study, about 93% to 94% showed CTE. Researchers adjusted that figure to estimate the rate across the broader group of deceased players.

That adjustment is the point of the new paper. Earlier work based on donated brains found CTE at much higher rates, including a 2017 study in which 99% of former NFL players' donated brains showed signs of the disease. But brain donation often comes after a family has seen troubling symptoms. The new estimate is still an estimate, not a direct count of every former player's brain.

What it means: CTE is linked to repeated blows to the head and involves abnormal accumulations of tau protein in the brain. It can affect memory, concentration, mood and impulse control, but the presence of CTE-related brain changes does not necessarily mean someone had dementia or noticeable symptoms during life. The study estimated that about 27% of the former players in its analysis had dementia, which can have several causes.

CTE can only be definitively diagnosed after death because its microscopic brain changes cannot yet be reliably identified in living people. That limitation matters here: the findings do not establish how many living former players, active NFL players, youth players or other contact-sport athletes have CTE. Experts also noted that players whose careers ended decades ago may not face the same risks as more recent generations, after rule changes and equipment such as Guardian Caps were introduced.

The NFL's response: The league said it continues to work on reducing concussions and head impacts through rule changes and protective equipment. The number to watch is whether researchers can develop a reliable way to identify CTE during life, when treatment and support could actually reach the person affected.