(Reuters) - An American Medical Association study on head injuries released on Thursday found career participation in the NFL was not associated with a statistically significant increase in death rates, at least when compared with other football players who spent less time in the league.
By the numbers
The study compared 2,933 athletes who played in the National Football League for an average of five years to 879 ?replacement players? who filled in for three games during a mid-1980s strike, finding no statistically significant difference in rates of death from all causes.
Critics said the AMA study had several flaws and pointed to a separate study released last year that found 99 percent of deceased former NFL players whose brains were analyzed post-mortem showed signs of chronic traumatic encephalopathy, a disease linked to repeated hits to the head that can lead to aggression and dementia.
The NFL, which has been accused of tolerating head injuries as part of the sport, has changed rules ahead of the Super Bowl on Sunday in Minneapolis, requiring players who show signs of a seizure to be pulled from the game.
At future games, athletes who stumble to the ground when trying to stand will be examined in their team locker room, the league said last month. More neurotrauma consultants not affiliated with specific teams will be on the field and at the NFL?s command center to monitor players.
The NFL was not immediately available to comment on the latest study.
Chris Nowinski, chief executive officer of the Concussion Legacy Foundation, said that the AMA study was hampered because the career NFL players involved were too young to have died from the effects of CTE.
?But even if they were older the presence of the disease and what gets written on death certificate are two separate things,? Nowinski said. ?That?s a well-established problem in looking at death records and trying to establish dementia.?
Nowinski also said that even the replacement players likely had spent eight to 12 years playing competitive football - including high school, college and some time in professional leagues - meaning that they could have sustained nearly as much head trauma as the NFL veterans.
So far, CTE can be diagnosed only by taking brain tissue from a dead subject. A January study in the scientific journal Brain found more evidence that all hits to the head, not just those that cause concussions, can contribute to CTE.
The AMA study, which was published in the Journal of the American Medical Association, found that the leading cause of death among the NFL career players was cardiometric disease, followed by transportation injuries and unintentional injuries.
Among the replacement players the leading cause of death was cardiometric disease followed by self-harm and interpersonal violence and then neoplasms.