In the United States, a new study concerning American football players is making waves. Scientists have indeed claimed that at least one in four former players ends up suffering from brain degeneration. This concerns chronic traumatic encephalopathy (CTE), a disease that can be diagnosed with certainty only after death, through analysis of brain tissue.
A minimum prevalence rate of 24.5%
While numerous studies have previously been conducted on National Football League (NFL) players in the United States, research continues. On August 25, 2026, researchers from Harvard Medical School published a new study in the BMJ journal, notably summarized in a TIME magazine article. The authors state that at least one in four players who died between 2016 and 2021 suffered from chronic traumatic encephalopathy (CTE).
The study involved 878 former players, of whom 235 donated their brains to science. CTE was definitively confirmed in 215 of these donors, i.e., more than 91% of the brains analyzed. By making a very conservative assumption that all the other deceased players who were not tested – about 600 individuals – were healthy, the minimum prevalence rate stands at 24.5%, i.e., roughly one in four.
“At a minimum, nearly a quarter of former NFL players who died between 2016 and 2021 showed neuropathological signs of chronic traumatic encephalopathy (CTE) at the time of death. Among NFL players who donated their brains, dementia diagnosed from medical records prior to death was common and associated with a stage IV CTE.”, the study notes.
A theoretical maximum rate of 97%
Recall that chronic traumatic encephalopathy is a progressive degenerative brain disease. It is triggered by repeated head injuries or sub-concussive blows and is characterized by the abnormal accumulation of tau proteins (the tau protein) in the folds of the brain. Normally present in the nervous system, this protein plays a fundamental role in the structure and function of neurons. However, when it undergoes structural changes, it becomes the main driver of several neurodegenerative diseases, including CTE and Alzheimer’s disease, among others.
CTE cannot be diagnosed with certainty until after death, via the analysis of brain tissue. Until now, brain banks suffered from a selection bias. In fact, families typically donated a brain if the player had shown dementia symptoms during life. The study authors therefore cross-matched donation data with death certificates for all players who died in the specified period. This allowed for the first time to establish a precise statistical prevalence for the entire league population. The researchers also stressed that the true rate lies somewhere between this minimum of 25% and a theoretical maximum of 97%, unsurprisingly far higher than that of the general population (about 1%).
Finally, it should be noted that since the early 2000s, CTE has haunted the world of American football and, by extension, the NFL. Aware of the rising incidence of the disease, the league introduced in 2011 a protocol for managing concussions. This protocol calls for removing players who have experienced a hit and show signs of a potential concussion. Today, the total number of NFL players whose deaths are linked to CTE remains unknown.
