Years of repeated head impacts raise CTE risk — even if they're not concussions

Two soccer players battling to head the ball.

High-impact sports like American football, soccer and rugby often involve repeated blows to the head, and although these impacts don't always cause concussions, a new study shows that even minor hits can damage the brain.

Until now, researchers thought chronic traumatic encephalopathy (CTE) — a degenerative brain disease linked to repeated head trauma that is characterized by mood, behavior, thinking and memory problems — began mainly with the buildup of abnormal protein in the brain. This protein, called tau, normally helps keep neurons healthy, but in its abnormal form, it can kill them. In fact, CTE can only be diagnosed with certainty after death, because at that time, doctors can directly examine tau protein levels in the brain tissue.