It's easy to imagine how blinding blows to the head can lead to severe brain injury, but new research suggests that even minor hits may, over time, lead to long-term problems.
Doctors say repeated head trauma, like the everyday minor hits sustained during a football or soccer season may someday lead to thinking and memory problems.
New research from Dr. Jeff Bazarian and his colleagues at the University of Rochester Medical Center in New York suggests a blow to the head appears to weaken the brain's natural protector and gatekeeper, called the blood-brain barrier.
For the study, he took blood samples from 67 college football players before and after games.
Even though none had suffered a concussion, those who took more hits to the head had higher levels of a protein that leaked from their brain into their blood stream.
"The body has never seen these proteins before, so it forms antibodies against it, just like if it were a virus," Dr. Bazarian says.
When that happens the body treats the protein as the enemy.
"The next thing that we think happens, is when that blood brain barrier opens up again with the next hit -- we think those antibodies now go back to the brain and attack," Dr. Bazarian explains.
If that theory proves true in future research it could lead to new ways to treat traumatic brain injuries, like drugs to block that "attack" response.
Previous studies have found football and soccer players can suffer 70 to 100 of these minor hits to the head during just one game.