The study of more than 3,400 long-term players between 1959 and 1988 found the risk of death from neurodegenerative disease was triple that seen in the general population, and adds to a burgeoning body of research linking contact sports to chronic brain disease.
"Our results are consistent with those from other studies," said Everett Lehman, an epidemiologist with the National Institute for Occupational Safety and Health in Cincinnati and lead author of the study published today in the journal Neurology. "No one study can make a definitive conclusion about whether concussions cause neurodegenerative disease; the body of literature is what's important."
Of the 334 players who died during the study follow-up, 27 had neurodegenerative diseases that caused or contributed to their deaths, according to the study. The risk of death from Alzheimer's or ALS was nearly four times higher among former NFLers. There was no increased risk of death from Parkinson's disease.
But the players' concussion histories were unknown, raising the possibility that factors other than head trauma might be at play.
"We can't directly link concussions and neurodegenerative disease," said Lehman, explaining how his study relied on death certificates to probe the incidence of neurodegenerative disease. "I think preventing concussions is a logical step to take, but whether that will result in a reduction in chronic neurological disease remains to be determined."
The median age of death from all causes was 54, according to the study.
Previous studies have linked contact sports to chronic traumatic encephalopathy or CTE – a progressive brain disease with features of Alzheimer's, ALS and Parkinson's disease. Lehman said it's possible some of the NFLers in his study had CTE, which can only be diagnosed by a brain autopsy.
"There's no way of knowing," he said. "The symptoms are all very similar."
CTE can also manifest as rage and depression. In February 2011, former Chicago Bears defensive back Dave Duerson fatally shot himself in the chest, leaving a note requesting his brain be sent to the "NFL brain bank" for study. His is one of 19 brains of former NFL players tested for CTE at the Boston University Center for the Study of Traumatic Encephalopathy, and one of 18 that tested positive.
Former San Diego Charger Junior Seau's brain was also donated to the brain bank after his suicide in May. The results are pending.
Growing awareness of the long term impact of concussions has prompted some former NFLers to sue the league, claiming it downplayed the risks. Other players have signed up to donate their brains to research – a gift they hope will bolster concussion research and protect future athletes.
And the NFL today announced it would donate $30 million to support research on medical conditions affecting athletes, including concussions and late-life neurodegenerative diseases.
"We hope this grant will help accelerate the medical community's pursuit of pioneering research to enhance the health of athletes past, present and future," NFL commissioner Roger Goodell said in a statement. "This research will extend beyond the NFL playing field and benefit athletes at all levels and others, including members of our military."