Former National Football League players are at least three times more likely to die of degenerative brain diseases such as Alzheimer's, Parkinson's and Lou Gehrig's disease, according to a study published Sept. 5 in the journal Neurology.


The study examined 3,439 NFL players who played at least five seasons between 1959 and 1988. By looking at their health conditions and causes of mortality by the end of 2007, the study found that the rate of all neurodegenerative mortality for this population of players was three times higher than the general U.S. population. The risk of Alzheimer's disease and amyotrophic lateral sclerosis (better known as ALS or Lou Gehrig's disease) was four times higher.


Of the 334 players who had died before the end of 2007, seven died from Alzheimer's, seven from ALS and three from Parkinson's, according to their death certificates. While those don't appear to be large numbers, lead author Elliot Lehman of the CDC's National Institute of Occupational Safety and Health told CNN they are statistically relevant, even more so when you consider that the average age of death of the NFL players was 57. "These are generally rare diseases, especially at the younger age. Even when looking at the general population, you're generally going to have small numbers."


The researchers also found that the death rate from these diseases was higher in quarterbacks, running backs players and other "speed positions."

The study did not look at players' medical records to see if they had experienced concussions during games.


A neurology professor who was not involved in the study told CNN that the study's authors are making an assumption of causality but do not conclusively prove it. 


Robert Stern, co-founder of the Boston University Center for the Study of Traumatic Encephalopathy, told The New York Times that the study's cutoff date of 1988 might make it irrelevant to today's players, who are significantly larger and stronger than players from more than three decades ago.


Lehman himself told HealthDay that modern-day NFL rules to protect players from concussions should improve players' long-term health as compared to past generations of players. "They've tightened up the rules on hits and blocks to the head, and many more of those are penalized now than previously," he said.


The NFL recently announced it would donate $30 million to the Foundation for the National Institutes of Health for research into brain injuries and related topics. An NFL spokesperson told Bloomberg News that the study "underscores the continuing need to invest in research, education and advocacy, strengthen and enforce our rules on player safety and do all we can to make our game safer."


Related sports injury stories on MNN:

Study finds NFL players three times as likely to die of brain disorders
The risk of Alzheimer's and amyotrophic lateral sclerosis (Lou Gehrig's disease) was four times higher than the general population.