New data from the United States' largest repository of human brain samples has shown that an overwhelming majority of NFL players who submitted their brains for analysis after their death suffered from chronic traumatic encephalopathy (CTE). The Department of Veterans Affairs' brain repository, based in Massachusetts, found that 76 of 79 former pro players had evidence of the condition, which can be caused by repeated head trauma.

The findings came as part of a wider study in which the department examined the brains of 128 deceased football players who had played the game at professional, semi-professional, college, or high school level. It found that even in the brains of those that had played at lower standards, the rate of CTE was high — of the 128 players, 101 tested positive for the disease. The brain condition is caused when blows to the head cause the production of tau, a protein that manifests as dense tangles around the brain's normal cells and blood vessels. The degenerative condition can cause depression and fits of rage among its sufferers, and confusion, memory loss, and dementia later in life.

The Department of Veterans Affairs' findings come from a weighted testing group — the experiments were conducted on brains donated to the brain repository by players and families who suspected the presence of the condition — but neuropathologist Dr. Ann McKee, who directs the brain bank, says that there's a correlation between playing football and developing CTE. "Playing football, and the higher the level you play football and the longer you play football, the higher your risk."

The NFL is currently responding to a lawsuit brought against it by more than 4,500 ex-players. The new Department of Veterans Affairs' report comes two weeks before an October 14th deadline at which thousands of NFL retirees have to decide whether to agree to the league's proposed settlement. Frontline says the ex-players have accused the league of hiding links between football and CTE, but these findings could help address "a key sticking point" in negotiations now that the league has acknowledged long-term concussion effects. Data filed in a federal court this month shows the NFL actually "expects nearly a third of all retired players to develop a long-term cognitive problem, such as Alzheimer's disease or dementia, as a result of football."

Recent advances in medical science have allowed doctors to preliminarily detect CTE while the sufferer is still alive, but Frontline says the condition can currently only be conclusively detected after death. Autopsies on a number of high-profile NFL players have shown that they were suffering from CTE, which might have influenced their behaviour. Chris Henry, a wide receiver for the Cincinatti Bengals, was found to have evidence of the condition in his brain when he died at 26. Henry's once-promising career was blighted by arrests for assault and drug use before he died from injuries sustained a car crash in 2009. Earlier this week, ESPN reported that ex-Kansas City Chiefs linebacker Jovan Belcher, who shot and killed his girlfriend before turning his gun on himself in the Chiefs' parking lot last year, was suffering from CTE when he died. Mike Webster, the Steelers center whose autopsy in 2002 kickstarted the investigation into degenerative brain diseases in football players, died homeless and living in a truck.

Other players who suspected they might be left permanently suffering from the after-effects of repeated blows to the head committed suicide in such a way that their brains could be left to science. Dave Duerson and Junior Seau, both top-level defensive players who spent a decade or more in the NFL, shot themselves in the chest so their brains could be studied after death, in the hopes of helping others avoid or manage CTE.