In a study published by medical journal JAMA, chronic traumatic encephalopathy (CTE) was found in 99% of deceased NFL players' brains that were donated to scientific research.
According to CNN, each brain studied was required to have football as its main exposure to head trauma. 202 total brains of deceased football players, including high school, college and professional, were studied. A whopping 177 were diagnosed with CTE.
It should be noted the study points out potential bias since relatives of players could have submitted the brains due to clinical symptoms they noticed while the players were alive.
Regardless, the JAMA study's results are alarming, especially since it is the largest CTE study to date.