The largest study yet of dead former NFL players found that over 99% had permanent brain damage

It’s the most damning evidence against the American football establishment to date.

A new study has found that 110 of 111 deceased former National Football League (NFL) players had evidence of chronic traumatic encephalopathy (CTE), or permanent brain damage as a result of repeated blunt force injuries to the head. Such injuries can result in behavioral changes or cognitive decline, like memory loss or dementia.

The study, by a team of researchers led by Boston University and the Veteran’s Association in Boston, was published July 25 in the Journal of the American Medical Association. The researchers were looking at the association of CTE in football players in general, and were funded in part by both the Concussion Legacy Foundation and the NFL itself. More broadly, they found that 177 of 202 deceased players who played at any level (including college and semi-professional) for an average 15 years (ranging from roughly 10 to 20 years) also had evidence of CTE.

Researchers conducted the study in two parts. First, a team of neuroscientists interviewed family members about the football players’ health and behavior. They asked for evidence of any kind of substance abuse, Parkinson’s disease, PTSD, sleep disorders, and even chronic headaches. Next, a separate team blinded to the interview results performed examinations on the late players’ brains and looked for evidence researchers previously decided were indicative of CTE—things like the lesions or patterns of tangled or darkened fibers in the brain.

CTE falls on a spectrum, and—unsurprisingly—professional football players tended to have some of the most severe brain damage compared to players at the semiprofessional or college level. Eighty-six percent of professional players had severe CTE, whereas only 56% of other groups of players did (excluding former high school players, of whom three out of 14 had any kind of CTE). In total, 84 of the 202 players had severe CTE. According to family interviews, 89% of these players showed either behavioral or cognitive changes, and 85% of them showed signs of dementia. Among the other 27 players who had only mild CTE, 95% of them had changes in their mental health, such as signs of depression or anxiety.

This evidence is the largest to date that suggests that playing American football leads to lasting brain damage. Back in 2015, research found that 87 out of 91 players who had donated their bodies to science had evidence of CTE as well.

The NFL has settled lawsuits with former players, agreed to insure them for concussions and other injuries they incurred for up to $5 million, and even put a new concussion protocol in place to try to intervene when players do get hurt. But according to SB Nation, this protocol works only some of the time. Medical professionals have to give players the all-clear before they return to the field, but players have an incentive to try to stay in the game.

There is, of course, a chance that this sample is biased: Players’ families may have decided to donate their loved ones’ bodies to the study because they believed that there was a link between American football and brain injury, or that their loved ones suffered from the condition.

CTE can only be diagnosed after death, and there’s no evidence that shows conclusively that rough play in football directly causes permanent brain damage. However, given the strong correlation between people playing football and suffering these types of injuries, it’s increasingly hard to ignore the mounting evidence of a link.

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