Current football helmets don't adequately protect against hits to the side of the head, which can lead to sometimes-lethal concussions and brain swelling, researchers have found.

Ten helmets in tests reduced the likelihood of traumatic brain injury by an average of 20 percent compared with no helmet in a simulation using crash test dummies. The most effective helmet reduced the risk by only 30 percent.

Concussion risks in sports are under increasing scrutiny as some deaths among young football players have been deemed preventable. New research has found abnormalities in the brains of former NFL players compared with those who didn't play the game. Current tests of helmets focus on impacts that lead to broken skulls, and don't adequately assess the chances of traumatic brain injury, researchers said.

"None of them are fantastic, sadly, and maybe that's the take-home message," said John Lloyd, the study author and research director at San Antonio, Florida-based Brains Inc. "Maybe if football players realized that their helmet only reduced their concussion risk by 20 to 30 percent, they'd lead with the head less often."

Professional sports leagues, including the NFL and Major League Baseball, have changed their medical protocols for treating players with head injuries in response to concussion data. Football is the deadliest sport among youths, and 12 percent of football deaths are caused by head or neck injuries involving students who returned to the game after a concussion. Helmets may provide another target to make sports safer, Lloyd said.

The research will presented at the annual meeting of the American Academy of Neurology, which is based in Minneapolis.

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