Former NFL players appear to be at an unusually high risk of dying from Alzheimer's, Parkinson's or Lou Gehrig's disease, suggests a new study that once again highlights the dangers of the game of football.

The study, which appears in the journal Neurology, found that the death rate from those three diseases among a group of former NFL players was about three times what one would expect from the general population.

The study looked at 3,439 former players who had at least five playing seasons from 1959-1988 with the NFL. The average age of the study participants was 57 and only 334 players – about 10 per cent of them – have now died.

Researchers compared the players’ deaths to a comparable group of American men and found that in 10 of the former NFL players, either Alzheimer's, Parkinson's or Lou Gehrig's disease (also called ALS) was listed as the cause of death.

That’s about three times the general rate for American men, the researchers reported.

While Alzheimer’s disease, Parkinson’s and Lou Gehrig's disease were shown as the official causes of death on the death certificates, the authors of this study say it’s possible that chronic traumatic encephalopathy (CTE) -- the degenerative brain disease linked to head injuries -- may have been the true “primary or secondary factor” in some of these deaths.

The researchers point out that the symptoms of CTE are often similar to those of Alzheimer’s, Parkinson’s and ALS. Only a brain autopsy can properly diagnose CTE and the researchers in this study did not have access to any autopsy info on the players.

Study author Everett J. Lehman, with the National Institute for Occupational Safety and Health in Cincinnati, said his team’s study wasn’t able to conclusively prove that the players’ deaths were caused by football-related concussions.

“We were not able to make the direct connection with concussions in our study. We were not able to assess concussions among these players,” Lehman told CTV’s Canada AM Thursday from Cincinnati.

“But we did acknowledge that a number of other current research studies have made a connection directly with concussions and brain degenerative diseases.”

The study also found that those players who played in “speed positions,” such as quarterbacks, running backs, wide receivers, and linebackers, were more than three times more likely to die from a neurodegenerative cause than non-speed position players.

Lehman notes that previous studies have also found that such players are a higher risk of brain diseases than “non-speed positions” such as linemen.

“The theory behind this is that those players are able to build up momentum prior to making a big block or a tackle, thus putting them at higher risk of concussion,” he said.

“Linemen aren’t at higher risk because, even though they engage each other a lot during the play, they’re not able to build up a lot of momentum prior to hitting each other.”

Lehman points out that his study was limited by the small number of deaths in the analysis and that it’s often difficult to make any conclusions based on one study.

“You really need to look at the entire body of research,’ he said. “What we did say about our study is that the results are consistent with what’s being found in the other research: that there is an increased risk of neurodegenerative diseases in football players.”

The study comes as the NFL begins a new season. On Wednesday, the league announced a donation of $30 million for medical research to the Foundation for the National Institutes of Health, the fundraising arm of the NIH.

NFL Commissioner Roger Goodell said the research could benefit athletes and potential areas of study may include CTE, concussion management and treatment and disorders from later in life such as Alzheimer's.

The study was supported by the National Institute for Occupational Safety and Health.