New Study: At Least 1 in 4 Former NFL Players Who Died 2016-2021 Had CTE

Researchers at Mass General Brigham published a study Tuesday in The BMJ putting a hard number on something the NFL has spent two decades trying not to talk about. At least 25% of former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy, the degenerative brain disease known as CTE.

The figure is built off death certificates, demographic data, and brain donations, according to NPR.

How they got the number

CTE can only be diagnosed after death, via brain dissection. That's the core problem researchers have wrestled with for years. Most CTE data has come from brain banks, and brain banks skew toward families who already suspected something was wrong, usually because a father, husband, or son showed memory loss, rage, depression, or other red flags before he died.

That selection bias means older CTE prevalence numbers, some running as high as 90%, were never a real population estimate. They were a snapshot of the worst cases.

Dr. Daniel Daneshvar, the study's lead author and chair of physical medicine and rehabilitation at Mass General Brigham, set out to fix that. His team pulled every former NFL player who appeared in at least one game since 1949, cross-referenced CDC death certificates, and built a list of 1,712 players who died between 2016 and 2021, according to NPR. They narrowed to that window because it's when brain donation rates were highest, giving them the best shot at an honest denominator.

Of the 878 former players who died in that period, 235 donated their brains, and researchers found CTE in 215 of them, according to Reuters, carried by Yahoo Sports. Applying that donation-based rate across the full population of deceased players gets you to the 25% floor.

Why researchers say the real number is higher

Daneshvar was blunt that 25% is a minimum, not a ceiling, according to NPR. The study also flagged 215 death certificates belonging to players who never donated their brains but whose certificates listed a neurodegenerative disease as cause of death, a pattern consistent with undiagnosed CTE.

At the brain bank level, the numbers are far starker. Of more than 330 NFL player brains donated to the UNITE Brain Bank at Boston University between 2008 and 2021, 93% came back positive for CTE, according to both NPR and CBC News. That figure isn't the population estimate. It's the heavily self-selected sample the population estimate was built to correct for. Previous headlines have typically used this number, which is why the new BMJ study matters: it's the first attempt to separate "how common is CTE in people who suspected they had it" from "how common is CTE in every player who ever suited up."

Where the damage comes from

Daneshvar told Reuters that NFL players die from neurodegenerative disease at roughly four times the rate of the general population. But he was equally clear about where the head trauma actually piles up.

"The bulk of the head impacts that these former NFL players experienced didn't occur at the NFL level," Daneshvar said, according to Reuters. "They occurred at the collegiate level ... and at the high school level and in many cases the youth level. And all of those cumulative hits to the head added up to result in an increased risk."

This finding reframes the debate. It's not purely an NFL problem to fix with better helmets and stricter concussion protocols at the pro level, though the league has made changes there too. The 2011 Collective Bargaining Agreement limited contact practices during the season, and the Ivy League has banned full-contact tackling in practice, according to Reuters. The exposure that matters most, according to the study's own author, starts in Pop Warner leagues and high school locker rooms, long before any of these men signed an NFL contract.

What the league says, and what's unresolved

An NFL spokesperson told Reuters the league "continuously strives to make the game of football safer," citing efforts to reduce concussions and head impacts, and said the NFL is "committed to ensuring that the NFL community has access to a robust — and expanding — set of resources" for players concerned about their health. The league did not dispute the study's findings or methodology in that statement.

CBC News noted the study also found dementia was common among the brain donors, and researchers are urging prevention measures focused on reducing repetitive head impacts at every level of the sport, not just the pros.

What isn't resolved: how much higher than 25% the true number actually is. The study's authors themselves call it a floor. Until more former players' brains are studied regardless of whether their families suspected symptoms, the ceiling stays unknown, and so does the real scope of the risk facing every kid who puts on pads before he's old enough to drive.