Research conducted on almost 100 deceased NFL players revealed that over 95 percent of them tested positive for the degenerative brain disease known as chronic traumatic encephalopathy (CTE).
In a study published by Frontline on Friday, a total of 87 out of 91 players were found to have the disease. The CTE research was carried out by the Department of Veterans Affairs and Boston University.
The chief of neuropathology at the VA Boston Healthcare System, Dr. Ann McKee, told Frontline that CTE is a "very real disease."
"People think that we're blowing this out of proportion, that this is a very rare disease and that we're sensationalizing it," McKee said. "My response is that where I sit, this is a very real disease. We have had no problem identifying it in hundreds of players."
Although research had suggested that concussions were one of the likely causes of CTE, new evidence suggests that "minor head trauma that occurs regularly in football may pose" a greater risk than the occasional violent collision.
The study noted that 40 percent of the positive tests were done on offensive or defensive linemen, who are subject to violent collisions on almost every play in a football game.
In a statement, the NFL said that it continues to strive to make game safer.
"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," the league said. "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."
In 2010, the league donated $1 million to the same brain bank that helped carry out the research published by Frontline.
Although the high number of CTE cases should be alarming for the NFL, researchers did note that the research was slightly skewered because many of the brains donated to the lab came from people who already believed they had the disease.
To put that in perspective, imagine if this study had been done with only former NFL kickers. CTE likely would've been found in far fewer brains, but that wouldn't mean it's not prevalent.
Even if the study's 95 percent number is a little high, it's still an alarming issue for the NFL -- and you can count former NFL tight end Tom Crabtree among those who are alarmed.
What an exciting way to start my weekend. I probably have CTE. https://t.co/1Ct0MK9qCT— Tom Crabtree (@itsCrab) September 18, 2015
Three former players who committed suicide in the past four years -- Dave Duerson, Ray Easterling and Junior Seau -- were all found to have CTE.