Scientists Studied 338 NFL Players’ Brains After Death. Nearly All Had the Same Disease

Football is one of America’s well-treasured pastimes. Research out today, however, highlights the hidden neurological costs that many professional football players have had to pay.

Scientists at Boston University, the Mayo Clinic, and others examined the medical records of hundreds of recently deceased former football players who donated their brains to science. Nearly all donors had died with chronic traumatic encephalopathy (CTE), they found, while a majority were also diagnosed with dementia. Roughly a quarter of all former football players who died between 2016 and 2021 at minimum had CTE, though the likelihood could be even higher, the researchers say.

“These findings indicate that NFL players have a higher prevalence of CTE at death than has been previously shown in multiple community based studies,” they wrote in their paper, published Tuesday in The BMJ.

CTE is a degenerative condition caused by repeated traumatic brain injuries. Though the condition has been described medically since the 1920s, it’s only in the past 20 years that researchers have conclusively tied CTE to high-impact sports like football.

Several high-profile deaths of former football players and other athletes with CTE have led to greater research on the condition. These efforts have included brain banks that allow former NFL players to donate their brains for study after they die. CTE, like many neurological conditions, can only be definitively confirmed by examining the brain post-mortem (that said, scientists are working to develop tests for living people).

The researchers conducted a sweeping analysis of all former NFL football players who debuted after 1949, when plastic, hard-shell helmets became mandatory, and who died between 2008 and 2021, totaling 1,712 people. This included 338 players who donated their brains to one of several banks, particularly the UNITE (Understanding Neurologic Injury and Traumatic Encephalopathy) brain bank housed at Boston University.

Neuropathologists on the research team were assigned to determine CTE status in the brain donors while being blinded to the players’ clinical medical history and football careers, and clinicians evaluated whether the donors had dementia while being blinded to the players’ CTE status.

All told, 93% of brain donors were diagnosed with CTE, including 31% who had severe stage IV CTE. Meanwhile, nearly 60% of donors met the criteria for dementia, and the odds of having dementia were significantly higher in players who had stage IV CTE. Notably, only 41% of the players who seemed to have dementia had neurological disease listed as a primary or secondary cause of death when they actually died. That might suggest that at least some of these deaths were wrongly classified.

Because CTE can only be confirmed with a brain autopsy, it’s not possible to know exactly how many former players who died between 2008 and 2021 had the condition. At minimum, based on the donor results, at least 18% had CTE. Looking only at the period between 2016 and 2021, when brain donation became much more common, that percentage shoots up to nearly 25%.