A study published in the British Medical Journal found that at least one in four former NFL players who died between 2016 and 2021 and donated their brains had CTE, with nearly two-thirds of those cases also meeting criteria for dementia. The research, conducted by Mass General Brigham, Boston University, and the Concussion Legacy Foundation, links the condition to repeated head impacts and notes it can only be diagnosed post-mortem. An NFL spokesperson stated the league continues efforts to reduce head impacts.