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Scientists Studied The Brains Of 111 NFL Players. 110 Had A Degenerative Brain Disease.


Tom Hale

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

The study looked at the brains of high school footballers to NFL legends. Aspen Photo/Shutterstock

“Punch drunk” is the old phrase used to describe boxers who appeared to be dazed, confused, and intoxicated after receiving blow after blow to the head for years. Now we understand this is actually chronic traumatic encephalopathy (CTE), a degenerative brain disease caused by repeated head trauma. Although the link to boxing is widely accepted, the connection between CTE and American football was only publicly acknowledged by the NFL in 2016.

Neurologists have just finished the largest study to date looking at the brains of former football players, including many who played for the NFL. Their study was published in the Journal of the American Medical Association (JAMA) on Tuesday.


Out of 202 deceased American football players, 177 were diagnosed with CTE. Out of the 111 NFL players, 110 showed signs of CTE. That’s 99 percent.

The study authors themselves note that the study has "trememndous selection bias" and limitations. All of the players in the study had their brains donated for research by their families, so they were perhaps more likely to opt into the study if the players had shown symptoms of CTE. That considered, the numbers are still startling.

Comparison of a "normal brain" and brain with CTE. Boston University Center for the Study of Traumatic Encephalopathy

The brains included high school footballers to NFL legends. Here’s how the figures break down: 3 of 14 high school players (21 percent) were diagnosed with CTE, 48 of 53 college players (91 percent), 9 of 14 semi-professional players (64 percent), 7 of 8 Canadian Football League players (88 percent), and 110 of 111 NFL players (99 percent).

Of those with severe CTE, 89 percent had behavioral symptoms, mood symptoms, or both. Around 95 percent had cognitive symptoms and 85 percent had signs of dementia. For the those with mild CTE, 96 percent had behavioral symptoms, mood symptoms, or both, while 85 percent had cognitive symptoms, and 33 percent showed signs of dementia.


The most common cause of death for participants with mild CTE pathology was suicide (27 percent) and for severe CTE it was a neurodegenerative disease (47 percent).

Since the link between CTE and contact sports has only been established relatively recently, larger scale studies such as this are important despite their limitations. Due to growing awareness, fresh efforts are seeing time and money pumped into the study of CTE and sports. Just last year, the NFL put forward $100 million for independent medical research into neuroscience-related topics.

"There are still many unanswered questions relating to the cause, incidence and prevalence of long-term effects of head trauma such as CTE," the NFL said in a statement in relation to this new study. "The NFL is committed to supporting scientific research into CTE and advancing progress in the prevention and treatment of head injuries."


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