The likelihood of CTE is raised by the force, not just the quantity, of head blows.

For years, researchers studying chronic traumatic encephalopathy, or CTE, believed the primary cause of it was repetitive hits to the head, whether or not those hits caused concussions. They believed the more frequently that a person sustained head blows, the more likely they were to develop neurological and cognitive struggles later in life.

A new collaborative study conducted by researchers at Boston University, Mass General Brigham, and Harvard Medical School—using brains donated to BU’s UNITE Brain Bank adds a new wrinkle to the research around CTE. The study found that the clearest predictor of what could cause a person to suffer brain disease later in life was the cumulative force of thousands of hits to the head, and not just the sheer volume of concussions suffered.

The study is the largest one to date, examining the root causes of CTE, which is associated with everything from memory loss to impulsive behavior to suicidal thoughts and depression.

By using data from 34 published studies that tracked blows to the head measured by sensors inside football helmets, the researchers were able to see how 631 former football players, whose brains were donated for research to BU, have been impacted. The study found that 71 percent of the brains examined—451 of the 631—had some level of CTE, while 180 showed no sign of the disease. The worst forms of CTE showed up in players who had absorbed the greatest cumulative force of hits to the head, meaning they were hit often and hard. (The individuals who absorb the hardest hits to the head are defensive backs, wide receivers, and running backs.)

Reference: Leveraging football accelerometer data to quantify associations between repetitive head impacts and chronic traumatic encephalopathy in males, Nature Communications, DOI 10.1038/s41467-023-39183-0