A study published Tuesday in the medical journal The BMJ found that at least 25% of former National Football League (NFL) players who died between 2016 and 2021 were diagnosed with chronic traumatic encephalopathy (CTE). Researchers from Mass General Brigham conducted the study to establish a more accurate baseline for the prevalence of the degenerative brain disease, which has long been linked to repeated head impacts but remains difficult to quantify.
CTE is a neurodegenerative condition that currently can only be diagnosed through a brain dissection after death. Previous research has relied heavily on brains donated to research banks, such as the UNITE Brain Bank at Boston University. Because these donations often come from families of individuals who displayed symptoms like memory loss or mood swings during their lives, researchers noted that earlier data may have been skewed by self-selection.
To determine the 25% figure, lead author Dr. Daniel Daneshvar and his team analyzed death certificates and demographic data for 1,712 former players who appeared in at least one NFL game since 1949 and died between 2016 and 2021. The study found a minimum prevalence of roughly 25%, though Daneshvar noted this is likely the "low end" of the actual figure. If researchers assumed every player had the disease except those definitively cleared, the maximum possible prevalence could be as high as 97%.
For living former players, the research highlights a distinction between permanent brain decay and treatable symptoms. Neuroepidemiologist Rachel Grashow noted that former players may experience symptoms similar to CTE—such as memory loss or mood changes—that are actually caused by treatable conditions like sleep apnea, high blood pressure, or low testosterone. These conditions are common among former athletes and tied to head injuries, meaning a person might notice improvements in their daily cognitive function and health by seeking treatment for these specific ailments rather than assuming they have an untreatable disease.
The study establishes a baseline for future policy and safety regulations within contact sports. An NFL spokesperson stated the league is committed to resources for player wellbeing and has implemented strategies to reduce head impacts, such as banning certain tackles and traditional kickoffs. However, the data primarily reflects players who competed before 2005, when CTE was first diagnosed in a former player. It remains unknown how more recent safety changes, such as the use of protective "Guardian Caps" or new tackling rules, will affect the prevalence of the disease for current players. The study concludes that further research is needed to assist living players in managing symptoms through their doctors.