Last week California joined Illinois as the second state to attempt to bring forward legislation to ban tackle football for kids under 12. Now, there is growing evidence to support the movement. A recent study has revealed a new reason why tackle football is dangerous for young kids.

A new study published in the Annals of Neurology has revealed that professional football players who played tackle football as kids suffered symptoms of brain disease much earlier than those that hadn’t. The study was part of Dr. Ann McKee’s ongoing and groundbreaking research on chronic traumatic encephalopathy or CTE in football players.

With the new awareness of CTE, many professional football player’s families have donated their brains to the study, which McKee has used to uncover her findings. According to the study, of the 211 brain samples analyzed, the 84 players who had played tackle football as kids showed symptoms, like cognitive and behavioral problems an average of 13 years earlier than the players who didn’t start until they were over the age of 12.

“It’s as though the brain of these people who started playing early football was less resilient to pathology,” says McKee, chief of neuropathology at Boston VA Healthcare System, and director of Boston University’s CTE Center. “It’s sort of like they have a weakened nervous system, and set you up for earlier onset of any of these disorders. That was a surprising finding.”

McKee’s research is ongoing as she attempts to learn more about how the game affects kids from an early age and how long they can play without significantly increasing their risk of developing CTE. However, according to McKee, there’s already enough evidence to support the idea of waiting until kids are older. “The data supports that you should not play tackle football until you’re more physically mature,” McKee told TIME.

—Shahrzad Warkentin

Featured photo: Pixabay


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