First concussions, then sub-concussive hits, and now contact delivered by 10-year-olds: It looks like blows to the head are never good for your brain, no matter how mild they may seem.

A new study of retired NFL veterans found that the worst cases of cognitive functioning were found in retirees who started playing football before they were 12. The study's findings suggest that the brain is affected by many more hits suffered during play than was previously thought.

NFL vets who started playing at an early age scored well below the marks of their counterparts -- about 20 percent worse, on average. The study involved 42 former NFL players between ages 41 and 65.

The reduced cognitive performance of those who started football before 12 was "significantly worse" on every test administered, according to the study. The participants featured an even mix of NFL players who started football before 12, and those who started after.

The age of 12 was selected because it is considered a critical point in brain development for males. At 12, boys are believed to have completed crucial periods of brain development. Injuries suffered before this point in life can result in longer recoveries and greater associated problems.

According to Robert Stern, the study's senior author, the conclusion is obvious: "The earlier you start, the more issues you may have," according to The New York Times.

The study provides an important counterpoint to the NFL's lauding of declining concussion rates the past two years. Concussions may well be down, but that might not solve the brain injury crisis that is afflicting the league.

Youth football participation may see further reluctance from parents who accept the study at face value, prompting a continued decline in youth football enrollment and greater calls to reform the game.

To Stern, the call-to-action is a no-brainer.

"It makes logical sense that kids, during a time of rapid brain development, should not be exposed to hit after hit after hit to their head," he said. "The idea of dropping kids off at a field during a very important period of maturation and fostering hit after hit after hit, it doesn’t make sense to me, personally."

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