A study on former NFL players' brains found that 99% had signs of degenerative disease

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Dave Duerson's brain was one of those examined and diagnosed with CTE at BU.

The latest study from an ongoing Boston University examination of the brains of former football players has yielded more ominous results.

In a study published July 25 in the Journal of the American Medical Medical Association, investigators reported that 177 out 202 brains of deceased American football players showed signs of chronic traumatic encephalopathy or CTE, the degenerative brain disease that's strongly linked to repeated blows to the head.

For former NFL players, the results were even more stark: 110 out 111 players' brains were diagnosed with the disease.

At varying levels of severity, CTE manifests with memory problems, mood disorders, depression, and dementia. There's still a lot we don't know about the disease and its causes, but this new data gives scientists even more reason to think professional football players are likely to suffer from CTE. It also suggests that these athletes are likely to have more severe forms of degenerative brain disease than the average patient.

That's a big deal when talking about America's favorite sport. The NFL has been accused of denying or concealing the risks of head injuries in the past, which led to a $1 billion lawsuit between the league and thousands of former players. Football players like Junior Seau and Dave Duerson, who both committed suicide, asked that their brains be examined for signs of the disorder and were diagnosed with CTE after their deaths.

Chris Nowinski, the executive director of the Concussion Legacy Foundation and author of "Head Games: The Global Concussion Crisis," previously told Business Insider that it's hard to understand just how bad this sort of disease can be "until you live this every day and really hear the horror stories of what happens to families when things go wrong."

What the new study tells us

The longer and more seriously someone played football, the study found, the more likely they were to have severe CTE. People who stopped playing after high school all had mild pathology, while those who played in college, semiprofessional, and professional leagues mostly had severe CTE.

Even the individuals posthumously diagnosed with "mild" CTE had showed signs of behavior problems, cognitive issues, and mood disorders when they were alive. Substance use disorders, a likelihood of committing suicide, and impulsivity were also common. In addition to those traits, those with severe CTE were frequently diagnosed with dementia.

"It is no longer debatable whether or not there is a problem in football - there is a problem," Dr. Ann McKee, who led the study, told The New York Times. Even if CTE was expected to be somewhat common, the fact that 99% of NFL players in the study showed signs of the disease indicates that it's extremely prevalent among former players.

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How risky are concussions?

The brains that BU's CTE Center studied were all donated for research based on suspicions that the individuals they once belonged to might have developed the disorder. Unfortunately, CTE can only be diagnosed after death, but many of the players whose brains were examined displayed symptoms before death that are linked to the disorder.

So it's not a surprise that CTE was so common among this sample.

However, as the Times reports, approximately 1,300 former NFL players have died since the CTE Center began this research. Even if zero of the brains that were not examined in this study showed signs of CTE, that would still make the minimum CTE prevalence for former NFL players approximately 9%. The researchers suggest that's significantly higher than the rate in the general population. And it's likely the incidence is even higher than that.

What we still don't know

The NFL has already admitted that there's a link between playing football and developing CTE. But we still don't know what causes CTE in the first place.

It's possible that concussions, the bell-ringing hits that leave players confused and potentially knocked out, play a role. But it's perhaps even more likely that the degenerative condition is triggered by the hundreds or thousands of smaller hits to the head that players endure.

As the new study points out, the vast majority of football players aren't college or professional players. Most people who play football play at some point as kids or high school students but then stop. We don't yet know how risky that exposure is, but it could be dangerous.

"It's an ethical question, what is our culture comfortable with," Nowiski told Business Insider. "Is government underwriting brain damage for children through school sports?"

Oher sports may be risky as well. CTE was first identified as "dementia pugilistica" in former boxers, and at least one study found that 17% of former boxers' brains showed the disease. Concerns have also been raised about the consequences of heading the ball in soccer and about contact sports like hockey and rugby.

It's important to understand these overall risks and to compare them to the health and social problems associated with avoiding sports. Perhaps the games can be changed in ways that make them less dangerous - youth football leagues have already made an effort to do boost safety and have reduced concussion rates. But how do we decide when an activity is safe enough?

No one wants to suffer the effects of a degenerative brain disorder. If there's a way to help athletes avoid that, we need to figure out the best way to do so.