For decades, the national conversation surrounding professional football, repeated head impacts, and brain health existed in a fog of speculation, denial, and statistical debate. While high-profile tragedies and postmortem diagnoses kept the dangers of head trauma in the headlines, skeptics routinely pointed out a fundamental epidemiological flaw: brain donation banks were heavily biased. Families were far more likely to donate the brains of deceased players who had displayed severe cognitive or behavioral symptoms, creating what scientists call a selection bias.
Now, groundbreaking new research published in The BMJ cuts through that uncertainty. The landmark study evaluates the entire population of former National Football League (NFL) players who died over a 14-year period, establishing for the first time a definitive baseline for the prevalence of Chronic Traumatic Encephalopathy (CTE). The findings confirm what health advocates have long feared: at minimum, nearly one in four former NFL players who died in recent years suffered from CTE.
Establishing the Ground Floor of CTE Prevalence
The study, led by Dr. Daniel H. Daneshvar and a team of researchers from Harvard Medical School, Boston University, and other leading institutions, analyzed data from 1,712 former NFL players who died between 2008 and 2021. Of those decedents, 338 donated their brains for neuropathological examination across multiple brain banks, including the UNITE Brain Bank and the UCSF Alzheimer’s Disease Research Center.
Pathologists confirmed CTE in 315—or 93.2%—of the donated brains. To overcome the inherent selection bias of brain donation, the researchers calculated the minimum and maximum possible prevalence of the disease across the entire population of deceased players.
Under the most conservative assumption imaginable—assuming that every single player who died and did not donate their brain was completely free of the disease—the minimum prevalence of CTE among NFL players who died between 2016 and 2021 was 24.5%. Conversely, the maximum theoretical prevalence reached 97.7%.
Researchers emphasize that the true rate lies somewhere in the middle, but establishing a minimum bound of 24.5% provides an alarming “floor” for public health experts.
“The true rate of CTE at death in NFL players is somewhere in the middle,” noted Dr. Daneshvar.
The Molecular Footprint and Diagnostic Challenges
CTE is a progressive neurodegenerative disease characterized by the abnormal accumulation of hyperphosphorylated tau (p-tau) protein in neurons around small blood vessels, particularly at the depths of the cortical sulci. Unlike Alzheimer’s disease or other forms of dementia, CTE possesses a unique pathognomonic lesion that sets it apart under microscopic evaluation.
Despite advances in pathology, diagnosing CTE in living individuals remains one of neurology’s greatest challenges. Because definitive diagnosis currently requires direct postmortem examination of brain tissue, clinicians in life must rely on clinical criteria for Traumatic Encephalopathy Syndrome (TES) to evaluate suspected cases.
Recent scientific reviews highlight how football causes progressive neurodegeneration: repeated subconcussive head impacts—the routine, everyday collisions experienced by linemen and running backs—may do as much or more cumulative damage over time as catastrophic, overt concussions. These micro-traumas disrupt cellular membranes, trigger neuroinflammation, and initiate the misfolding and aggregation of tau proteins that slowly spread through brain tissue over several decades.
High Severity Pathology Directly Drives Dementia
The BMJ study went beyond simply counting cases; it established a clear clinicopathological link between advanced CTE pathology and severe clinical outcomes in life. Among the 338 brain donors evaluated, nearly 60% had been clinically diagnosed with dementia prior to death.
To account for selection pressure, researchers used inverse probability weighting to adjust for variables such as age at death, player position, length of career, and cause of death. The analysis revealed that players with Stage IV CTE—the most severe stage of the disease—had a 44% higher risk of dementia compared to those without Stage IV pathology (Risk Ratio 1.44, 95% CI 1.16 to 1.78). Furthermore, Stage IV CTE was strongly associated with significant functional impairment and executive dysfunction, measured via validated clinical scales including the Functional Activities Questionnaire and the Behavior Rating Inventory of Executive Function.
Surprisingly, total playing duration was not significantly associated with whether a player developed CTE at all, but it was strongly linked to whether they developed severe Stage IV CTE (Risk Ratio 1.07, 95% CI 1.04 to 1.09). This suggests that once an athlete crosses a critical threshold of exposure to repetitive head impacts at the elite level, individual genetic or environmental factors may dictate whether the disease takes root, while continued exposure accelerates its severity.
Death Certificates Severely Undercount the Crisis
One of the study’s most striking revelations lies in how neurodegenerative diseases are documented on official records. Historical attempts to estimate dementia and CTE rates in former athletes heavily relied on the National Death Index (NDI) and state death certificates.
However, when researchers compared study clinician-adjudicated dementia diagnoses against official death certificates, they found that death certificates captured only 40.6% of donors with clinician-diagnosed dementia as either a primary or secondary cause of death. Over 58% of donors whose death certificates listed cardiovascular disease, and 52% of those whose death certificates listed fatal accidental injuries (often resulting from nursing home falls), actually suffered from adjudicated dementia in life.
This massive underreporting on death certificates demonstrates that previous epidemiological studies vastly underestimated the true burden of neurodegenerative disease among contact sport athletes.
Contextualizing the Study’s Broader Impact
To put these figures into perspective, community-based brain bank studies—such as those conducted by the Framingham Heart Study or Kaiser Permanente—have found CTE in fewer than 0.6% to 1.3% of general population donors who lacked documented exposure to repetitive head impacts. The finding that at least 24.5%—and potentially far more—of professional football players develop CTE highlights an extraordinarily elevated risk tied directly to contact sports.
Beyond CTE, comorbid pathologies were rampant in the donor cohort. Nearly 17% of donors suffered from Lewy body disease, 15% had co-occurring Alzheimer’s disease, and over 54% exhibited moderate to severe arteriolosclerosis. This high rate of mixed neuropathology indicates that repetitive head impacts may set off a cascade of multi-pathology brain injury, compounding vascular and neurodegenerative decline as players age.
As public awareness grows and biomarker research advances toward an in-life diagnostic tool, this landmark study serves as an undeniable baseline. It transforms the debate from whether brain disease is widespread among professional football players to how sports organizations, medical professionals, and policy makers will act to prevent it.
Endnotes and References
- Daneshvar, D. H., Nowinski, C. J., Abdolmohammadi, B., Luster, C. B., Uretsky, M., Martin, B. M., Palmisano, J. N., Weuve, J., McClean, M. D., Cherry, J. D., Dwyer, B., Feigel, E. D., Mastrodicasa, M. J., Alvarez, V. E., Rabinovici, G. D., Seeley, W. W., Grinberg, L. T., Crary, J. F., Stein, T. D., Goldstein, L., Katz, D. I., Zafonte, R. D., Tripodis, Y., Cantu, R. C., Stern, R. A., Alosco, M. L., McKee, A. C., & Mez, J. (2026). Prevalence of chronic traumatic encephalopathy at death in National Football League players: retrospective population based cohort study, 2008-21. BMJ, 394, e100418. https://doi.org/10.1136/bmj-2026-100418
- National Public Radio (NPR). (2026, August 25). Study finds at least 1 in 4 former NFL players who died had CTE. https://www.npr.org/2026/08/25/nx-s1-5943168/cte-nfl-concussions-deaths-study
- Science Magazine. (2026). How does football cause brain disease—and why is it so hard to diagnose? https://www.science.org/content/article/how-does-football-cause-brain-disease-and-why-it-so-hard-diagnose