At least one in four NFL players who died from 2016 to 2021 had CTE

At least one in four former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy, according to a study in The BMJ that set out to measure prevalence without relying only on brains that families chose to donate.

Daniel Daneshvar of Massachusetts General Hospital and colleagues identified 878 former players who died in those six years. They obtained 235 brains. CTE was diagnosed in 215 of those brains. The conservative figure the paper leads with is simple arithmetic: 215 of 878 is 24.5 percent. If every undonated brain had been free of the disease, that would still be the floor. The ceiling, if every undonated brain had it, is 97.7 percent. The true share sits somewhere in that range. In people who do not take repeated blows to the head, CTE at death is under 1 percent.

Ann McKee, who directs Boston University's CTE Center and is a co-author, has said the design was meant to blunt the selection-bias charge that followed earlier brain-bank papers. Those papers found CTE in nearly every donated football brain. Families who donate are more likely to have watched a relative decline. By starting from every death in a six-year window, then adding the donated subset, the new paper can state a minimum that does not depend on that filter.

What the stages show

Stage IV pathology, the most severe form, was tied to dementia symptoms, with a risk ratio of 1.44. CTE can be diagnosed only after death, by examining tissue. In life the symptoms overlap with Alzheimer's disease and other dementias, which is why the prevalence question has been so hard to close.

A wider look at 1,712 former players who died from 2008 to 2021 produced a possible range of 18.5 to 98.7 percent. The 2016-2021 window is the one the authors trust more, because donation rates were higher. Donors had to have played at least one NFL game after 1949, the year hard-shell plastic helmets became mandatory.

The largest predictor, the authors and outside researchers keep repeating, is not a single concussion. It is the cumulative force of hits over a career. That is a harder fact for a league to price than a spectacular helmet-to-helmet foul, because it is the ordinary play, repeated thousands of times.

What the league now has to answer

Daneshvar called the numbers a wake-up call and said money should move toward treatment and, eventually, a cure. The NFL has spent two decades arguing that rule changes, helmet design and spotters have reduced risk. This paper does not measure those changes. It measures the men who already played.

Families of current players now have a floor: at least a quarter of the men who died in a recent six-year stretch had the disease. They also have a ceiling that is close to everyone. The gap between 24.5 and 97.7 percent is the research problem that remains. Filling it requires more brains from men who died without a public neurological story. Until those brains are studied, the honest statement is the one the paper already made. The minimum is one in four. The rest is not yet counted.