Deadly Brain Disease Shadows NFL Legends

At least one in four NFL players who died between 2016 and 2021 had a brain disease that can only be found after death.

Quick Take

A new study in The BMJ found that at least 24.5% of former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy, or CTE.
Researchers studied 235 donated brains out of 878 former players who died in that window, and 215 of them showed signs of CTE.
The true rate could be far higher, with the study’s upper estimate reaching nearly 98%, since most families did not donate brains.
Boston University researchers who pioneered CTE research warn that donated brains are not a random sample, so the numbers should not be read as exact odds for every player.

What The New Study Actually Found

Researchers from Boston University and Mass General Brigham tracked 878 former NFL players who died between 2016 and 2021. Families of 235 of those players agreed to donate brain tissue for study. Of those donated brains, 215 showed signs of CTE, a degenerative disease tied to repeated head impacts. That gives a diagnosis rate of over 91% among donors alone.

But the researchers didn’t stop at the donor pool. They built a population-wide estimate using all 878 deaths as the denominator, not just the brains examined. That math produces the headline number: at least 24.5% of every former player who died in that period, whether or not their brain was studied, likely had CTE. The high end of their range reaches 97.7%.

Why The Lower Number Is Considered The Safe Bet

The 24.5% figure counts as a floor because it assumes zero cases among every unexamined brain, the most cautious assumption possible. Sports reporters covering the study called this the “low end,” with authors themselves saying the real number likely sits “somewhere in the middle” of their wide range. That framing matters. A quarter of dead players confirmed with CTE, treated as a bare minimum, is a very different story than a soft guess.

What makes this study different from earlier CTE research is the denominator itself. Past studies, including Boston University’s famous 2017 finding of CTE in 110 of 111 donated NFL brains, only measured the donor pool. This new paper anchors its estimate to every player who died in the study window, whether or not a family chose to donate. That shift toward a full population count is what elevates this from anecdote to something closer to science.

The Honest Weakness Every Reader Should Know

Brain donation is not random. Families who suspect a loved one suffered from head trauma, memory loss, or mood changes are simply more likely to hand over a brain for study than families with no such worries. Boston University’s own researchers have said this selection bias could push earlier estimates in either direction, and they’ve explicitly warned against assuming that 91% donor rates apply to every living or deceased NFL player.

That doesn’t mean the finding is wrong. It means the true prevalence sits somewhere inside a wide range, and nobody can currently pin it down with precision. The study cannot separate NFL-specific damage from a lifetime of hits absorbed in Pop Warner leagues, high school, and college. It also cannot tell us how many living retirees carry the disease, since CTE remains diagnosable only after death, using today’s tools.

What This Means For Families And The League

For parents weighing whether to let a kid play tackle football, or for retirees wondering about their own memory lapses, this study offers real data instead of speculation. A conservative one-in-four rate among a defined group of NFL decedents is not a scare tactic. It’s a measured, peer-reviewed number built on a clearer methodology than past donor-only studies.

This deserves serious attention from the league, players’ union, and youth football organizers, not dismissal as advocacy noise. At the same time, honest reporting means acknowledging the uncertainty baked into the estimate rather than rounding it up to a scarier number than the data supports. The responsible reading sits exactly where the researchers placed it: a real problem, a confirmed minimum, and a range that demands more study before anyone claims certainty.

Thread grounded: A study estimate that one in four former NFL players developed CTE sparked debate over sampling bias and the true prevalence.

Sides
• Misleading headline: The sample cannot represent every former NFL player.

• Understated risk: The donated brains showed CTE…

— BREAKLING (@BREAKLINGx) August 28, 2026

Independent replication using a broader, less donor-biased sample would settle much of this debate. Until that happens, the smartest move for fans, players, and policymakers is treating 24.5% as a floor worth taking seriously, while resisting the urge to round it up to near-certainty based on the upper bound alone.