Despite NFL settlement, still no proof football causes Alzheimer's or CTE

"The lawsuit is not a scientific issue, it's a legal and political issue," Randolph said. "There is absolutely no credible scientific data to suggest an increase of neurological risk from playing professional football."

Under the tentative settlement, the NFL would pay up to $5 million for each player who has Alzheimer's disease and up to $4 million for each death from chronic traumatic encephalopathy (CTE). But a recent study by Randolph and colleagues of retired NFL football players found no evidence that CTE even exists. The study was published in the Journal of the International Neuropsychological Society.

Randolph said there currently are no conclusive data that retired NFL players suffer a unique neuropathology. CTE is a vague condition, with no established clinical criteria and no consistent pathological criteria to diagnose it. And recent studies have found that NFL players have overall mortality rates that are only half of expected rates based upon men in the general population. Suicide rates are only about 40 percent of the rates in the general population.

"We still do not know if NFL players have an increased risk of late-life neurodegenerative disorders," Randolph said. "If there is a risk, it probably is not a great risk. And there is essentially no evidence to support the existence of any unique clinical disorder such as CTE."