The brain disease chronic traumatic encephalopathy, believed to be caused by repeated head trauma, has been found in 87 of 91 deceased former NFL players tested, according to researchers.
"People think that we're blowing this out of proportion, that this is a very rare disease and that we're sensationalizing it," Dr. Ann McKee, chief of neurophysiology at the VA Boston Healthcare System and director of the lab where the tests were conducted, told PBS' "Frontline." "My response is that where I sit, this is a very real disease. We have had no problem identifying it in hundreds of players."
In research conducted by the Department of Veteran Affairs and Boston University, 40% of those testing positive for CTE were offensive or defensive linemen, according to the report.
Though those linemen aren't typically subjected to the big concussion-causing hits sustained by other players on the field, it's the consistent minor collisions that could pose a greater risk to players, according to the research.
The disease has been also been found in 79% of those tested who played football at any level going back to high school. For former NFL players tested, that number rises to 96%.
Signs of the disease's existence in living players can be identified with brain scans but CTE cannot be officially diagnosed until after death.
The suicides of Hall of Fame linebacker Junior Seau in 2012 and former Chicago Bears safety Dave Duerson in 2011, who were both diagnosed with CTE following their shooting deaths, helped raise awareness of the neurodegenerative disease.
Many former NFL players have filed lawsuits against the league because of head injuries they sustained during their playing days, which they believe are the cause of other problems including headaches, dementia and amyotrophic lateral sclerosis.
In April, a settlement agreement between the NFL and nearly 5,000 former players as part of a class-action lawsuit was approved by a federal judge. The agreement could reportedly cost the league up to $1 billion.
The NFL issued a statement to "Frontline": "We are dedicated to making football safer and continue to take steps to protect players, including rule changes, advanced sideline technology, and expanded medical resources. We continue to make significant investments in independent research through our gifts to Boston University, the [National Institutes of Health] and other efforts to accelerate the science and understanding of these issues."
The NFL said the number of concussions suffered by players dropped 25% last season and by 36% over a three-year period.
Follow Matt Wilhalme on Twitter @mattwilhalme.
MORE FROM SPORTS