So much for glory days on the gridiron. Playing pro football makes it far more likely than normal a brain can turn into mush. And there’s elevated likelihood these once powerful bodies will shut themselves down with Lou Gehrig’s disease.    Disturbing new data from the National Institute of Occupational Safety and Health lab in Cincinnati says retired NFL players are dying from Alzheimer disease and amyotrophic lateral sclerosis at rates four times higher than the U.S. population. Other neurodegenerative diseases kill retired NFL players at about twice the norm. The study appears in this month’s issue of Neurology, a medical journal affiliated with the American Academy of Neurology. Overall, retired football players live longer and are healthier than most Americans, especially the linemen. But some of the players who passed, caught and defended are clearly beset by excessive amounts of neurodegenerative disorders later in the lives.   Former quarterbacks, running backs, fullbacks, receivers, defensive backs, linebackers and safeties comprise the biggest group of former players who suffer. All were in the so-called “speed” positions, players who took hits that included high-acceleration head impacts.    For the pro football study, the Cincinnati-based research team looked at health records of 3,439 retired NFL players who had five seasons in the league between 1959 and 1988. The researchers tracked down 334 death certificates across the nation. Of those, 17 had a neurodegenerative disorder listed as the cause of death; 14 had been in speed positions.   (Cardiovascular disease claimed 126 of the ex-NFL players; cancer took 85).   The NIOSH team said their findings add to a growing collection of evidence that shows football players face an increased risk of neurodegenerative disease. Most previous studies have focused on long-term health effects of repeated concussions. Besides finding increased death rates from Alzheimer’s, ALS (which often is called Lou Gehrig’s Disease) and Parkinson disease (about three times the national rate), the Cincinnati scientists raised an entirely new concern. They said football players have elevated death rates from chronic traumatic encephalopathy, which is a pathologically distinct neurodegenerative condition. It sets in years after head-knocking and is linked to a progressive decline in neuron functioning. It can change the ability to think and makes it difficult to move about because the brain doesn’t work as it should.    Chronic traumatic encephalopathy, which goes by the initials CTE, isn’t reported on many death certificates because the diagnosis has only been recently recognized.       Everett J. Lehman was lead author of the study; others who worked on it were Misty Hein, Sherry L. Baron and Christine M. Gersic.  The researchers said their findings cannot be applied to other professional sports. And the team says more information is needed about the impact of football injuries: “Because our cohort was limited to longer-term professional players, our findings may not be applicable to other professional and nonprofessional football players. However, recent autopsy studies have reported pathologic findings of CTE in college-age and professional football players with relatively short playing careers. We did not have data on player injuries and conductions.  If chronic mild to moderate concussion is an actual risk factor for neurodegenerative mortality, the magnitude of the risk may depend on the intensity and frequency of brain injuries incurred over a number of years. … Finally, we did not have information on environmental, genetic or other risk factors for neurologic disorders.”NIOSH did not say it found a cause and effect for the higher than normal number of Alzheimer and ALS deaths. But the scientists said they had no doubt “that professional football players are at an increased risk of death from neurodegenerative causes.”