The rough game of American Football may have caused a rare brain disease that can lead to memory loss and dementia in more than 95% of players tested. Scientist detected CTE (chronic traumatic encephalopathy) in brain tissue of 87 out of 91 former players tested.

The disease, which is caused by repeated head trauma, is mainly detected among former National Football League stars, because of the repeated smaller collisions that generally occur on the field. Neuropathology chief at the VA Boston Healthcare System Dr Ann McKee, who led the research, said that the team faced a lot of scrutiny with the public claiming that they are "blowing this out of proportion".

The criticism is based on CTE being a very rare disease, and McKee's team has been accused of sensationalising the effects. However, McKee responded: "This is a very real disease. We have had no problem identifying it in hundreds of players."

Cost of football

The research results add to concern raised by NFL veterans as well as researchers that the sport causes significant damage to players' brain. The issues were highlighted in March, when 24-year-old San Francisco 49'ers linebacker Chris Borland announced his resignation, saying he is concerned about the effect the violent game would have on his health.

In April, the NFL was the subject of a class-action lawsuit settlement that would see the league pay $1bn to thousands of former footballers who may have long-term brain damage after suffering serious concussions during games. The payment, which gives each player up to $5m, settles some 300 court actions brought by more than 5,000 ex-players that were combined into a single case. The judge did not introduce a cap on the total amount to be paid.

NFL will 'protect players'

However, it is not just the pros who should be worried. McKee's research also found that almost 80% of tested players from amateur, semi-professional and professional levels had symptoms of CTE in their brain tissue. In a statement, a spokesman for the NFL said that the league is dedicating to making the sport safer for players.

"We… continue to take steps to protect players, including rule changes, advanced sideline technology, and expanded medical resources," the spokesman said. "We… 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 2013 a book by ESPN reporters Mark Fainaru-Wada and Steve Fainaru, League of Denial, detailed the story of the trauma and mental decline of American football star Mike Webster, and the subsequent revelations that his problems were caused by injuries sustained during his football career. The book's story was also featured in a documentary made for the US public broadcaster PBS.