With the NFL preseason in full swing, I can’t help thinking about the incremental neurological damage that’s being inflicted on the players with each vicious tackle and violent collision. The damage — chronic traumatic encephalopathy, the degenerative brain disease better known as CTE — has often been decades in the making.
Chris Nowinski, the former professional wrestler-turned-neuroscientist who now runs the Concussion and CTE Foundation, knows the grim arithmetic only too well. He observes that the risk of developing CTE appears to climb with every additional season of football played, and among the hundreds of former players that Boston University scientists have examined, more than half of those who played twelve seasons or longer turned out to have the disease.
CTE isn’t caused by a single blow to the head. It’s the accumulation of thousands of smaller ones, hits that didn’t register as concussions but that imperceptibly and invisibly damaged brain tissue over years. In some people, for reasons researchers still don’t fully understand, that deterioration doesn’t stop when the blows stop. It keeps progressing, causing the brain to degenerate in a manner disturbingly similar to Alzheimer’s disease.
Here is where the science gets uncomfortable for a nation that organizes its autumn Saturdays and Sundays around football: Nobody can say with certainty how often CTE produces violent behavior, because there is no way to diagnose the disease in a living person. Researchers only learn about a case after a family donates the brain for post-mortem examination, and by then, they’re reconstructing personality changes from secondhand memory, sometimes decades removed from the behavior in question. That makes the data inherently incomplete and selection-biased — families are more likely to donate when something clearly went wrong.
But the anecdotal pattern is hard to ignore. Nowinski has personally known men from the CTE brain bank who killed others before killing themselves, including a former wrestling colleague who murdered his family. Having studied the disease for 20 years and known some of its victims personally, Nowinski doesn’t believe these homicides happen in the absence of underlying brain damage.
None of this is abstract for Nowinski, who played football at Harvard. Two of his own teammates have since been diagnosed with CTE after dying under difficult circumstances. He describes a “tremendous sense of urgency” to find a way to diagnose the disease in the living and eventually develop real treatments, because he knows he may be looking at his own future, or a friend’s.
That urgency ought to extend well beyond the NFL and the research lab, into every Pop Warner sideline and youth soccer field in the country. A 2023 study published in JAMA Neurology examined the brains of 152 deceased contact-sport athletes under age 30 and found CTE pathology in 63 of them — most cases mild, but present across football, soccer, hockey, rugby, and wrestling. Those findings are accompanied by an important asterisk: It does not mean that four in ten young athletes are developing CTE. It means that among a highly selected group of families willing to donate a young person’s brain — usually because something had already gone wrong — the disease showed up far more often than anyone would like.
There is also a straightforward fix available for the youngest kids, and Nowinski is blunt about it: Stop allowing children to be hit in the head repeatedly. I was reminded of that admonition recently when, at a local park, I witnessed a soccer coach repeatedly tossing a ball to a teenage girl who “headed” it back to him. During the five minutes or so I watched the back-and-forth, she probably took at least 50 hits to the head.
Data from the CDC comparing youth tackle football to less violent flag football found that players aged 6 to 14 in tackle leagues absorbed roughly 15 times as many head impacts, and 23 times as many high-magnitude impacts, as kids playing flag. Hockey and soccer organizations have already adopted minimum age or other restrictions for body checking and hits to the head, reflecting growing concern about concussions, repetitive head impacts, and their possible long-term neurological consequences, including CTE. Youth football, by and large, has not — kids as young as five are still being taught to tackle.
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The obstacle isn’t scientific ignorance so much as institutional denial. The NFL now formally recognizes football’s link to CTE, but the National Federation of State High School Associations, the body that governs most American high school sports, does not. That gap matters because it shapes what coaches are trained to do and what parents are told before they hand a five-year-old a helmet.
CTE research still cannot calculate an individual child’s risk. But the state of our current knowledge should settle one argument: Pre-teen children have no business absorbing repeated blows to the head in the name of sport. In the vast majority of cases, we are simply raising kids, not professional athletes-to-be, and we are giving some of them, silently and irreversibly, a disease with no cure.
Henry I. Miller, a physician and molecular biologist, is the Glenn Swogger Distinguished Fellow at the Science Literacy Project. He was the founding director of the FDA’s Office of Biotechnology.