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Researchers at Boston University have found more evidence supporting a link between repeated knocks to the head and chronic brain disease.
The results, just published in the journal Brain, add weight to concerns about the effect of repeated mild head trauma in athletes, whether they're pros or peewees.
"The sheer volume of cases I think is going to just overwhelm anybody that wants to be in denial about the existence of this problem," Dr. Robert C. Cantu, a co-director of Boston University's Center for the Study of Traumatic Encephalopathy told ESPN.
Researchers, including Cantu, looked at brain samples taken after death from 85 people (ages 17 to 98) who had experienced repetitive mild traumatic brain injury, such as concussions, throughout their lives. They compared those samples with others from similarly aged people without a history of brain injuries.
The group with a history of head trauma included 17-year-old Nathan Stiles (a high school player who died after a 2010 head injury), 1960s running back Cookie Gilchrist, and other notable professional athletes.
The group was dominated by athletes: 80 altogether, including some men who were also in the military.
Roughly 80 percent (or 68) of all the people with histories of hits to the head showed evidence of chronic traumatic encephalopathy (CTE for short), which results in gradual degradation of brain tissue.
CTE's mildest symptoms include headache and attention problems. In more advanced stages of CTE, people can experience depression, dementia and aggression.
The researchers found evidence of CTE in 50 American football players — 33 of whom played in the National Football League.
"This study clearly shows that for some athletes and war fighters, there may be severe and devastating long-term consequences of repetitive brain trauma that has traditionally been considered only mild," the authors of the study concluded.
The findings come amid controversy over the effect of head trauma on younger players and growing scientific evidence of persistent brain injury in athletes.
There's also a consolidated lawsuit by former players against the NFL. Thousands of them allege that the league withheld data suggesting that head trauma could lead to brain damage.
CTE has been seen in athletes before, but the latest findings of an association with head trauma is the most extensive one to date. "By understanding its evolution from isolated focal disease to widespread devastating disease associated with dementia," Ann McKee, a neuropathologist who led the BU study, told Shots in an email. "We now have much clearer ideas about how to identify this disease in living people and how to treat it."
Even so, the researchers agree that it's hard to know how widespread the problem may be. "It's a gambler's game to try to predict what percentage of the population has this," Chris Nowinski, a co-author of the study and co-director of the Boston University center, told the New York Times.