MAYWOOD, Ill. (CBSDC) – There is not enough evidence to establish a link between football and the increase risk of chronic traumatic encephalopathy (CTE), says a new study.

Previous information had shown that National Football League 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.

But researchers from Loyola University Medical Center are reporting only limited evidence showing a link between the two.

A previous study, of 3,439 retired NFL players, who played at least 5 seasons between 1959 and 1988, researchers found that the overall risk of death associated with neurodegenerative disorders was three times higher among these retired than players than the general U.S. population. Alzheimer’s disease and ALS was four times higher for the NFL players.

Christopher Randolph, a PhD from Loyola, and a professor in the university’s Department of Neurology, and Stella Karantzoulis, PhD, of New York University School of Medicine, found that suicide rates were actually substantially lower among the athletes than the general population. “Given that suicidality is described as a key feature of CTE, this finding is difficult to reconcile with the high rates of CTE that have been speculated to occur in these retired athletes,” Karantzoulis and Randolph write in their study. “It is likely that there are a diverse set of risk factors for suicidality, such as life stress, financial difficulty, depression, chronic pain, and drug abuse, in retired athletes.”

Karantzoulis and Randolph examined symptoms of retired NFL players who had mild cognitive impairment and said that symptoms seen in the retired players were virtually the same as those observed in non-athletes. They write that these findings cast doubt on the notion that CTE is a novel condition unique to athletes who have experienced concussions.

Previous studies sugest that trauma triggers progressive degeneration of the brain tissue, including the build-up of an abnormal protein called tau. The brain degeneration is associated with memory loss, confusion, impaired judgment, impulse control problems, aggression, depression, and progressive dementia.

Karantzoulis and Randolph write that the presence of abnormal tau proteins in the brain may not be a reliable indicator of CTE. “Older persons without dementia can accumulate Alzheimer’s disease pathology without any associated cognitive or clinical symptoms,” they write in their study. “The actual clinical significance of ‘abnormal’ tau deposition in the brains of retired athletes therefore remains unclear.”

“One cannot deny that boxing and other contact sports can potentially result in some type of injury to the brain,” Karantzoulis and Randolph go on to write. “Three currently are no carefully controlled data, however, to indicate a definitive association between sport-related concussion and increased risk for late-life cognitive and neuropsychiatric impairment of any form.”

Boston University defines CTE as a progressive generative disease of the brain found in athletes with a history of repetitive brain trauma, including symptomatic concussions as well as asymptomatic subconcussive hits to the head.

The study titled “Modern Chronic Traumatic Encephalopathy in Retired Athletes: What is the Evidence?,” which showed limited evidence between sports concussions and an increased risk of late-life cognitive and neuropsychiatric impairments, was published in the journal Neuropsychology Review.