Almost all NFL players have rare brain disease caused by head trauma

CTL was found in 87 of the 91 deceased former NFL players tested

There's been a longstanding controversy over the injuries football players suffer (Getty Images)

A large majority of NFL players may suffer from chronic traumatic encephalopathy (CTE), a rare brain disease believed to be caused by repeated head trauma.

Researchers from the Department of Veteran Affairs and Boston University tested 91 dead former NFL players, and found it in 87 of them — that's 95 per cent.

Dr Ann McKee, chief of neurophysiology at the VA Boston Healthcare System and director of the lab where the tests were done, told PBS: "People think that we're blowing this out of proportion, that this is a very rare disease and that we’re sensationalizing it.

"My response is that where I sit, this is a very real disease. We have had no problem identifying it in hundreds of players."

One observation was that 40 per cent of those who had CTE were offensive or defensive linemen — positions that don't offer suffer big hits.

That has led researchers to conclude it's the repeated smaller head collisions that pose the greatest risk.

And it's not just pro-players. The disease has been identified in 79 per cent of those tested who played football at any level going all the way back to high school.

The disease cannot be officially diagnosed until after death, even though brain scans can give indications.

Many former NFL players have sued the league because of injuries sustained because of the health problems they get later in life — from severe headaches to dementia to amyotrophic lateral sclerosis.

In April, a class-action lawsuit between the NFL and nearly 5,000 former players was settled in a deal that could cost the league up to $1 billion.

The NFL told PBS: "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."