Study finds chronic traumatic encephalopathy in at least 24.5% of deceased NFL players

Prevalence findings and study cohort

At least one in four former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy (CTE), according to research published on Tuesday in the British Medical Journal. The investigation, conducted by Mass General Brigham, Boston University, and the Concussion and CTE Foundation, evaluated 878 former professional players who debuted after 1949 and appeared in at least one league game. Deceased athletes in the cohort died at ages ranging from their twenties to their eighties. Among that group, researchers examined post-mortem brain tissue from 235 donors and confirmed CTE in 215 individuals, representing 91.4% of the examined samples. The condition involves an abnormal buildup of tau protein around small blood vessels deep in the cerebral sulci. Because neuropathologists can identify CTE only through direct tissue examination after death, the disease cannot yet be diagnosed in living athletes.

Methodology and selection bias

Voluntary brain donation programs often attract families of players who exhibited cognitive decline before death, creating a selection bias. To address this limitation, the research team calculated a statistical range rather than treating the 91.4% donor rate as representative of all deceased players. Under the conservative assumption that none of the 643 unexamined players had the disease, CTE affected at least 24.5% of the overall cohort of 878 players. If every unexamined player had developed the condition, the theoretical mathematical ceiling would reach 97.7%.

The true number is somewhere in that range.

Lead author Daniel Daneshvar noted that the 24.5% baseline establishes a floor by assuming no unexamined players had the disease.

Clinical impact and amateur exposure

Clinical records of the examined donors showed frequent instances of dementia, memory loss, depression, and motor coordination problems. Research cited by the authors shows that former NFL players experience a mortality rate from neurodegenerative disease roughly four times higher than the general population. Daneshvar pointed out that neurological damage accumulates over years of athletic activity, with the majority of head impacts taking place before professional careers begin.

The bulk of the head impacts that these former NFL players experienced didn't occur at the NFL level. They occurred at the collegiate level... and at the high school level and in many cases the youth level. And all of those cumulative hits to the head added up to result in an increased risk.

Prevention and institutional measures

The study authors urged sports administrators to introduce stricter contact limits across youth, high school, and collegiate football. The NFL recognized the connection between football impacts and CTE in 2016, following a federal court settlement with thousands of retired players. The league had previously restricted full-contact practices in its 2011 collective bargaining agreement, and the Ivy League eliminated tackling in practices in 2016. In response to the study, league representatives said they continue to fund medical resources and pursue strategies to reduce concussions and head impacts.