A landmark study has put a hard floor under a question that has shadowed football for two decades: how common is CTE among the men who play it?
The NFL CTE study, published Tuesday in the medical journal The BMJ, found that at least one in four former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy, the degenerative brain disease linked to repeated head impacts. Researchers called it the largest ever effort to estimate the disease’s prevalence among deceased professional players, and they were blunt that the true figure is almost certainly higher.
Here is what the NFL CTE study actually found, why the number carries such a wide range, and what it does and does not tell us about the sport today.
What the NFL CTE Study Found
The researchers started with every player who appeared in at least one NFL game, debuted after 1949, and died in the six-year window from 2016 to 2021. That came to 878 men.
Of those, 215 had brains donated and examined, and 93.2 percent of the donated brains showed CTE. Extrapolated across the full group, that yields a minimum prevalence at death of 24.5 percent.
The ceiling is far higher. If every player whose brain was never examined also had the disease, the rate would reach 97.7 percent. The truth sits somewhere in between, which the authors said was the honest way to frame it.
Why the Range Is So Wide
The wide band comes from a problem researchers call selection bias.
Families who suspect something was wrong are more likely to donate a brain, so the donated pool is not a random sample. That is why the team reported a floor and a ceiling rather than a single tidy figure.
For context, community brain bank studies have found CTE in less than 1 percent of the general population. Against that baseline, even the conservative 24.5 percent floor is a striking jump for former NFL players.
The Dementia Link in the NFL CTE Study
A second finding may matter more day to day than the headline percentage.
More than 90 percent of players with stage IV CTE, the most advanced form, also carried a dementia diagnosis. But the relationship was messier at lower stages, and roughly 40 percent of donors with no CTE at all also had dementia.
The lesson researchers drew is that brain pathology and real-world symptoms are not the same thing. You cannot read one cleanly off the other.
What It Does Not Say
The NFL CTE study has real limits, and the authors named them.
Because CTE can still only be diagnosed after death, the research says nothing about how common the disease is in active players or living retirees. There is no validated test for the living.
The cohort skews old, too. The average age at death was around 66, meaning most of these careers unfolded before 2005, well before the league restricted kickoffs, banned helmet-to-helmet hits, and funded safer equipment research. As one researcher put it, the data may not represent the NFL of 2026.
For anyone who wants the wider public health frame, our earlier report on the Harvard study linking flight crew cancer risk to radiation shows how occupational exposure research reaches similar limits. The full paper is available through The BMJ, which published the peer-reviewed findings.
A quarter is the floor, not the ceiling, and the men counted here mostly played a rougher, less regulated game than today’s. Whether the reforms of the last twenty years have moved that number is the question this study was not built to answer, and the one that matters most to every player still on the field.
