National Football League (NFL) players are three times more likely to die from neurodegenerative diseases than the general US population and four times more likely to die from Alzheimer’s disease and amyotrophic lateral sclerosis (ALS), according to a study published in the September 5 online Neurology.
“Although the results of our study do not establish a cause-effect relationship between football-related concussion and death from neurodegenerative disorders, they do provide additional support for the finding that professional football players are at an increased risk of death from neurodegenerative causes,” said Everett J. Lehman, MS, an occupational epidemiologist at the National Institute for Occupational Safety and Health (NIOSH) in Cincinnati, part of the CDC.
Mortality Rates in the NFL
The researchers analyzed data from a cohort of 3,439 NFL players (39% African American) who played at least five seasons between 1959 and 1988. Using death certificates as well as the National Death Index, the investigators determined that 10% of the cohort was deceased as of the last analysis in 2007. The small percentage of deaths is due to the relatively young median age of the cohort (57) as of 2007.
Although the overall football player mortality rate was less than that of the general population of US men, analysis showed that the football players had a significantly increased mortality rate for all neurodegenerative causes combined—three times greater than that of the general population of US men. This increase in neurodegenerative mortality was evident using both underlying cause of death rate files and multiple cause of death rate files.
Furthermore, compared with the general population, football players had a four times greater mortality rate for Alzheimer’s disease and ALS. Mortality from Parkinson’s disease was increased but was not statistically significant.
Speed Versus Nonspeed Positions
One study found that nonline or “speed” position players are at higher risk of neurodegenerative mortality compared with line or “nonspeed” position players. While the study authors did not have information on the head injuries incurred by the players, they used position as a surrogate for likelihood of concussion. Speed players are able to build up considerable momentum before being tackled or tackling another player, while offensive and defensive linemen (“nonspeed” players) usually engage other players soon after the football is snapped, thus mitigating the potential to build up momentum to a tackle or a block, noted Mr. Lehman.
A number of other research studies that have collected head injury and concussion data for football positions have found, in general, that speed players are at higher risk of concussion than nonspeed players.
Those in the speed category, which included 62% of the cohort, played quarterback, running back, halfback, fullback, wide receiver, tight end, defensive back, safety, and linebacker, while the nonspeed category comprised all defensive and offensive linemen.
A Common Etiology?
Mr. Lehman noted that the analytical results for all neurodegenerative causes of death are more significant than results for individual diseases. “Other studies have shown that there may be a common etiology among one or more of the neurodegenerative diseases—though they may take different developmental paths due to unique environmental exposures or genetic susceptibility factors,” Mr. Lehman told Neurology Reviews.
In addition, recent studies suggest that chronic traumatic encephalopathy (CTE), a distinct disease with symptoms that resemble those of other neurodegenerative disorders, may have been the true primary or contributing cause of death in many cases. CTE is a more recently confirmed diagnosis and was not included as a possible cause of death on the players’ death certificates. “To account for possible reclassification, we reported combined results for all neurodegenerative causes,” wrote Mr. Lehman.
Mr. Lehman and his colleagues also did not have data on player concussions and injuries, so they were unable to offer conclusions on how players’ level of disease risk may correspond with years of brain injuries.
“Additional studies to quantify the cumulative effects of brain injuries—in particular, the relative effects of concussive and subconcussive-level injuries—will be of particular importance in understanding the underlying disease mechanisms not only in football, but also in other sports where head injuries are common, such as soccer, boxing, horse racing, and hockey,” Mr. Lehman said.
Lehman EJ, Hein MJ, Baron SL, Gersic CM. Neurodegenerative causes of death among retired National Football League players. Neurology. 2012 Sept 5 [Epub ahead of print].