Though several studies have linked brain injuries among the football players to their sport, for the first time the largest study of its kind has found clinical evidence to prove it.
After examining brains donated from 202 former players of the U.S., researchers found that 87% showed the diagnostic signs of chronic traumatic encephalopathy (CTE), a neuro-degenerative disease associated with repetitive head trauma. It is almost 99% among former National Football League (NFL) players in the sample.
Led by Boston University neuropathologist Ann McKee, researchers studied brains donated by families of former football players to a bank maintained by the VA Boston Healthcare System and the Concussion Legacy Foundation.
The researchers also tested for other neurodegenerative diseases including Alzheimer's and motor neuron diseases like amyotrophic lateral sclerosis and found that 45% of the men had these symptoms, suggesting that repeated traumatic brain injuries may cause other brain diseases, too.
The team defines CTE, a diagnosis made only at autopsy, as "progressive degeneration associated with repetitive head trauma." The lack of clear-cut pathology reference found in other neurodegenerative diseases like Parkinson's or Alzheimer's disease, has led many to seek more research into it.
"I think it is increasingly difficult to deny a link between CTE and repeated traumatic brain injury, be it through contact sports or other mechanisms," says Gil Rabinovici from the University of California, San Francisco (UCSF), who was not part of the study.
Apart from the NFL players, 48 of 53 brains of former college players, seven of eight who played professional football in Canada and nine of 14 semi-professional players showed the signs of CTE and of college and professional players were more extensively affected, they said. Nearly 86% of former professional players and 56% of college players had severe disease, said the team findings.
The results have been published in the Journal of the American Medical Association. Scientists said more research is now required to determine the incidence and prevalence of CTE both in football players and the general population.
In an earlier study conducted on 67 college football players in Cleveland in 2013 showed that concussions are the leading cause of brain damage in sports and football players may suffer long-term brain changes even in the absence of concussion.
Researchers from Cleveland Clinic's Lerner Research Institute found that the more hits to the head a player absorbed, the higher the levels of a particular brain protein that's known to leak into the bloodstream after a head injury. Some of them showed signs of an autoimmune response that has been associated with brain disorders.
The study, published on March 6, 2013, in the online journal PLOS ONE and sponsored by the National Institute of Neurological Disorders and Stroke (NINDS) tested the brain injuries employing several methods, including blood tests, brain scans, and tests to measure memory, motor control, reaction time, impulse control and balance, besides review of game video to assess head hits among the players in the study.