In 2009, Ann McKee, MD, director of the brain bank at the Bedford Veterans Affairs Medical Center, pulled out a photograph of a tissue sample from the brain of a deceased eighteen-year-old. “I’m not allowed to talk about how he died,” she explained to the writer Malcolm Gladwell, who’d met with McKee as part of his research for a piece about traumatic brain injury. “But this is completely inappropriate.”

The teenager had been a football player, McKee said, and the image of his brain showed the amount of decay usually found in patients who have reached advanced age. It was troubling. The brain of an otherwise-healthy young adult man should not show signs of neurodegenerative decline.

It is generally understood that people who sustain multiple blows to the head—like athletes who play contact sports, and combat veterans—have higher rates of Chronic Traumatic Encephalopathy (CTE). A neurodegenerative disease, CTE causes the early onset of symptoms that resemble Alzheimer’s, dementia, and Parkinson’s including impaired judgment, aggression, suicidality, and problems with memory and cognition. To neuropathologists like McKee who are trained to look for signs of CTE, the disease causes the brain to look as though it’s begun to decay. This is because, in fact, it has.

Recent animal research has led scientists to new understandings about CTE that were unreachable in previous studies, which relied solely on the examination of brains from human cadavers. The combination of data from animal experiments and empirical evidence from human subjects has led researchers to more sound conclusions about the risks associated with repetitive head trauma. Many of these findings are remarkable, carrying serious implications for public health and policy, especially as it pertains to competitive sports and athletics in general.

In 2009, McKee and her team had seen and analyzed thousands of brains. Still, she told Gladwell, they needed to see more cases involving football players before they could draw any airtight conclusions about head trauma and CTE. Other factors, like performance-enhancing drug use, or possibly a genetic predisposition to neurodegenerative disease, might also play a role.

Speaking before the House Judiciary Committee in 2009, McKee described another brain she’d examined. It belonged to a former NFL player, and showed signs of serious damage. In photographs taken without a microscope, tangled ropes of tau, the protein associated with Alzheimer’s, were visible. Littered across the organ were dark spots in which the tau tangles had built up. “May I remind you,” she asserted, “that in a normal 45-year-old, absolutely none of these changes would be found. In fact, you wouldn’t find any of these changes in a normal 65-year-old, 85-year-old, or 110-year-old.”

The brain’s deterioration, McKee said, followed the pattern of the other 10 former football players she’d examined. It’s only a total of 11 brains, she explained, but “I’ve only seen this unique pattern of change with this severity in individuals with a history of repetitive head trauma caused by football as well as boxing.”

Importantly, at that time head trauma told an incomplete story. Must it be severe enough to cause a concussion? How many blows can the brain handle? Is the direction or the angle of the hit important, in terms of whether it increases the risk for traumatic brain injury or CTE?

McKee has since built her case, publishing more than 35 studies on the subject and analyzing hundreds of brains that belonged to football players as well as other athletes who’d sustained repetitive blows to the head. In summer 2017, a story in The New York Times shook the football world: McKee’s lab had examined 111 brains of NFL players. 110 had CTE.

Approximately six months later, McKee joined a team of researchers from Boston University who, on Jan. 18, 2018, published a groundbreaking study with mice and humans that led them to some surprising conclusions. According to their research project, which spanned seven years, avoiding concussions is a misguided and potentially ineffective method of preventing CTE. Rather, the focus should be to prevent all blows to the head—especially in cases involving children and teens, whose brains are still developing.

In this study, research with animals allowed scientists to conduct controlled experiments to gauge the relative risk of CTE caused by certain kinds of head trauma. Since the condition can only be diagnosed post-mortem, animal studies offered a deeper insight into CTE than would be possible if the researchers had only examined the brains of dead football players: “We see it even after one exposure to the impact, and it not only persists, but it will progress,” explained Lee Goldstein, MD, PhD, who led the study. “It spreads through the brain. It will spread as you age.”

In this study, young mice exposed to very minor impacts showed signs of CTE, leading Goldstein and his team to conclude that minor head traumas that don’t cause concussions can very easily lead to degenerative brain disease. And in the United States, approximately 1.2 million children aged six to 12 play tackle football. Does the data from this study therefore have potential policy implications?

Drs. Goldstein and McKee were quoted in an article published by CNN on Jan. 18, 2018, the very same day their research appeared in the journal Brain. Their study’s findings had inspired a campaign by the Concussion Legacy Foundation, with support from NFL Hall of Famers and former players, to limit tackle football to children older than 13.

Conversations about CTE and football tend to focus on the injuries of collegiate and professional athletes. In recent years, as the risks for younger players have become better-known, fewer parents have elected to let their kids play. Medical professionals are perhaps especially cautious when it comes to contact sports, especially those who have witnessed, firsthand, what happens to the brain of a child who’s sustained repetitive head trauma.

In a July 2017 interview with the Boston Globe, McKee explains the moment in which she realized she could no longer call herself a football fan: “We got the brain of this kid, 13 years old. He was playing football and he just had this massive traumatic brain injury. He had the kind of injury you would have if you got into a motor vehicle accident. If a truck hit you…And I thought, I just can’t do this anymore. I just can’t.”

A sea change in public opinion regarding football, especially as pertains to youth participation in the sport, is possible. In mice, researchers have confirmed what had long been suspected about the relationship between football and CTE—by methods that would be impossible with human subjects. Past revelations about risks associated with spinal injury and concussions have been met with decisive action to better protect players from these injuries and to ensure they recover fully before going back onto the field. In this case, armed with new information gleaned from research with animals, policymakers and public health officials may be better equipped to protect the health and safety of American children.

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