The new football season is well underway, and with it comes the longstanding debate about the role football plays in long-term brain disease. Now, researchers report having found evidence of brain disease in 95% of brains tested belonging to former NFL players.

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The study supports past research that found repeated minor head trauma is the biggest risk to neurological health for footballers.

Researchers with the Department of Veterans Affairs and Boston University, MA, identified chronic traumatic encephalopathy (CTE) in 87 of 91 deceased NFL players, indicating that there is a link between football and long-term brain disease.

The findings were first reported by PBS and published on the website of the Concussion Legacy Foundation, whose brain bank received a $1 million research grant from the NFL in 2010.

“People think that we’re blowing this out of proportion, that this is a very rare disease and that we’re sensationalizing it,” says Dr. Ann McKee, chief of neuropathology at the Department of Veterans Affairs Boston Healthcare System. “My response is that where I sit, this is a very real disease. We have had no problem identifying it in hundreds of players.”

The team has previously identified CTE in the brains of football players who have donated their brains to science. So far, they have identified CTE in 96% of NFL players and 79% of football players examined to date – a total of 131 out of 165 individuals.

CTE occurs when an individual receives blows to the head over a period of time, causing progressive damage to nerve cells in the brain. The condition can impair cognitive functioning, causing difficulties with thinking and emotions and leading to problems such as depression and dementia.

The injuries that result in CTE cause the abnormal accumulation of proteins, interference in cell-to-cell communication and alter the white matter in the brain.

Previous research has suggested that repetitive minor head trauma represents a bigger risk to players than rare but violent collisions. The researchers found that 40% of the footballers who had CTE had played as offensive and defensive linemen – positions that experience physical contact on every play of a game – supporting past studies.

This research is not the first to put football under increased scrutiny concerning the health and welfare of its players. Earlier this year, Medical News Today reported on a study published in JAMA Neurology that found retired NFL players with a history of concussion were at an increased risk for brain shrinkage and memory problems.

A number of former NFL players have taken legal action against the league on account of injuries and related health problems they have developed in later life associated with the sport, conditions that include dementia and amyotrophic lateral sclerosis (ALS). In April, a $1 billion settlement with around 5,000 former players was approved.

The NFL gave the following statement in response to the findings:

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.”

CTE can only be fully diagnosed after death. Many of the former footballers who had donated their brains to research had concerns about possible neurological problems while alive. This potential selection bias means that the researchers cannot guarantee the population they have analyzed is representative of all footballers.

To determine the overall incidence of CTE among footballers, the researchers will need to analyze the brains of a number of players who had never exhibited any signs or symptoms of the disease.

Despite this potential limitation, Dr. McKee states that their figures are “remarkably consistent” with previous research. She told PBS that the biggest challenge that now remains is convincing people with a vested interest in football that CTE is “an actual disease.”

“People want to make this just Alzheimer’s disease or aging and not really a disease,” she says. “I think there’s fewer of those people, but that’s still one of our major hurdles.”

Previously, MNT reported on a study that found for soccer players, heading the ball is the most common cause of sustaining a concussion.