And just to complicate things further, there is another study that tracked Wisconsin high school football players from the 1950s. Those former players, surveyed decades later in their 60s, did not have different cognitive or depression outcomes compared to nonplayers. Likewise, another recent survey of 35 retired NFL players over the age of 50 did not find a link between the number of concussions a player incurred and his cognitive decline.

It is difficult to parse the research, let alone conduct it: CTE can only be diagnosed post-mortem. Unless scientists are looking at the actual brains of former players, argue researchers such as Dr. Lee Goldstein of Boston University School of Medicine’s CTE Center, they are not getting a complete picture.

Goldstein argues the case against football and other high-impact sports is open and shut. “Association is very clear. Risk increases with greater exposure, so if you don’t want to have this disease or any risk of it, you shouldn’t do it,” Goldstein said of playing football at any level.