domingo, 9 de septiembre de 2012

CDC - NIOSH Science Blog – Brain Injury in the NFL

CDC - NIOSH Science Blog – Brain Injury in the NFL

Brain Injury in the NFL

It’s that time of year again—football season. While pro, college and pee wee football players and fans across the country prepare for the annual rituals of the game, questions of safety linger on the sidelines. A new study from the National Institute for Occupational Safety and Health (NIOSH) finds that National Football League (NFL) players may be at a higher risk of death associated with Alzheimer’s and other impairments of the brain and nervous system than the general U.S. population. These results are consistent with recent studies by other research institutions that suggest an increased risk of neurodegenerative disease among professional football players.
The paper, “Neurodegenerative causes of death among retired National Football League playersExternal Web Site Icon,” published in the journal Neurology looked at a cohort of 3,439 NFL players with at least five playing seasons between 1959-1988. While NFL players on average live longer than the average American male, the new research found that the overall risk of death associated with neurodegenerative disorders was three times higher among the study group than the general U.S. population. The risk for two major subcategories, Alzheimer disease and ALS (also known as Lou Gehrig’s disease), was four times higher for the NFL players.
In addition to the overall comparison with the general population, the study also compared the deaths of players associated with neurodegenerative disorders based on playing positions. More neurodegenerative deaths were observed among players in “speed” positions (quarterback, running back, halfback, fullback, wide receiver, tight end, defensive back, safety, and linebacker) compared with players in “non-speed” positions (all defensive and offensive linemen). Other research studies have shown that speed players may be at higher risk of concussion since they can build considerable momentum prior to the point of being tackled or tackling another player. Offensive and defensive linemen usually engage other players soon after the football is snapped, mitigating the potential to build up momentum to a tackle or a block.

Study limitations

While our study is consistent with other recent studies that have found increased risk of neurodegeneration among NFL football players, our research has several limitations. Some of the limitations are listed below.
  • It is not possible to determine from our study the cause of the increased risk of death from neurodegenerative disorders. Research suggests that football players who have experienced one or more concussive blows to the head are at increased risk of neurologic disorders but our study does not establish a cause-effect relationship between football-related concussions and death from neurodegenerative disorders.
  • Since our cohort was limited to longer-term professional players, our findings may not be applicable to those who play for a shorter term or high school and college football players. The magnitude of risk may depend on the intensity and frequency of brain injuries incurred over a number of years.
  • The study relied on death certificate information for causes of death; at the time of analysis only 10 percent of the participants had died. Of the 334 players who had died, Alzheimer’s, ALS, and Parkinson’s Disease were listed for 17 of them. The small number of deaths used in the study only allowed us to place players into two broad position categories. We were not able to identify potentially important differences in neurodegenerative mortality risk across the various positions included within the speed position group.
  • Other studies have suggested that Chronic Traumatic Encephalopathy (CTE), which can exhibit symptoms similar to Alzheimer’s disease and ALS, may occur years after sustaining football-related concussions. Since CTE is a newly confirmed diagnosis, it is possible that some deaths attributed to Alzheimer’s or ALS on death certificates may actually have been related to CTE. A brain autopsy is necessary to diagnose CTE and distinguish it from Alzheimer’s or ALS; no death certificate would have listed CTE as a cause.
  • We did not have information on environmental, genetic or other risk factors for neurologic disorders.
Additional studies to quantify the cumulative effects of brain injuries, in particular the relative effects of concussive-level injuries, will be of particular importance in understanding the underlying disease mechanisms not only in football but other sports where head injuries are common such as soccer, boxing, horse racing and hockey.
Everett Lehman, MS
Mr. Lehman is an occupational epidemiologist and deputy division director in NIOSH’s Division of Surveillance, Hazard Evaluations & Field Studies.

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