Study Estimates Nearly 75 Percent of Deceased Former NFL Players Had CTE

Chronic traumatic encephalopathy, or CTE, is a degenerative brain disease linked to repeated blows to the head. It can affect football players, military personnel and others exposed to head trauma, and it can be diagnosed only after death, when microscopic changes in the brain become visible. A new study offers the first population-level estimate of how common the disease was among former National Football League players who died over a 16-year period.

JAMA Network Open reported on October 28, 2026, that an estimated 74.5 percent of the 2,362 former NFL players who died between January 2008 and December 2023 had CTE neuropathology. The estimate is not a raw count from donated brains. It is a statistical correction that tries to account for why families choose to donate: players with cognitive symptoms were about five times more likely to become brain donors than players without such symptoms.

That correction matters because earlier figures were drawn almost entirely from brain banks, where selection is not random. Science News reported on October 28, 2026, that a 2017 study had estimated 99 percent of former NFL players developed CTE based on donated brains, a figure that may have been skewed because families who donated may have done so after seeing CTE-related symptoms. The new analysis includes players whose brains were never donated, using National Death Index records to build a broader cohort.

The result is both striking and qualified. It places CTE in roughly three of every four deceased former players in the study window, far above the less than 1 percent found among community brain bank donors in the United States, Australia, Austria and Brazil. Independent experts told NBC News that it is the highest estimate to date, while cautioning that CTE can only be confirmed after death and that not everyone with pathology develops symptoms. NBC News reported on October 28, 2026, that the estimate was derived from a combination of brain bank data and national death records.

Key Facts

The study, titled Bias-Adjusted Prevalence of Chronic Traumatic Encephalopathy Among Deceased National Football League Players, was published online on October 28, 2026. It combines data from the Understanding Neurologic Injury and Traumatic Encephalopathy, or UNITE, brain bank with National Death Index records. Boston University School of Public Health said on October 28, 2026, that the work was led by Julia Gallini, a PhD candidate in biostatistics, with Yorghos Tripodis as senior author, in collaboration with Boston University, Mass General Brigham and the Concussion & CTE Foundation.

The cohort included 2,362 deceased former NFL players. Of those, 396 were brain donors and 1,966 were nondonors. Neuropathologic evaluation was available for 387 donors, and 362 of them, or 93.5 percent, had CTE. The players averaged 5.1 years in the league, and 971 players, or 41.1 percent, were 80 or older at death. Exposure was defined as playing at least one regular-season or postseason NFL game.

To move from the donor sample to the full cohort, the researchers estimated a median cognitive-symptom-related brain donation selection ratio of 4.97, with a 95 percent confidence interval of 4.72 to 5.26. After applying that adjustment, the bias-adjusted prevalence of CTE at death was 74.5 percent, with a 95 percent confidence interval of 69.6 percent to 78.3 percent. A conservative lower-bound analysis put the figure at 63.7 percent, with a range of 57.2 percent to 68.9 percent. Even if players with cognitive symptoms were 10 times more likely to donate, the paper states, estimated prevalence would still exceed 60 percent.

The study also estimated that 27.2 percent of former players had a history of all-cause dementia during life, with a 95 percent confidence interval of 22.6 percent to 31.6 percent. That is not a measure of dementia caused specifically by CTE. Sensitivity analyses across eight mild cognitive impairment enrichment scenarios produced CTE estimates ranging from 70.3 percent to 86.1 percent and dementia-history estimates ranging from 28.2 percent to 44.2 percent.

Analysis

The bigger picture here is that the debate over CTE prevalence has shifted from whether donated brains are unrepresentative to how much that bias matters. The authors do not claim that 74.5 percent is a precise count. They argue that selection bias materially inflates donor-based estimates but is unlikely to fully explain the high burden of CTE neuropathology among deceased former NFL players. That conclusion is stronger than a simple donor tally because it survives several adjustments, including a scenario in which donation is 10 times more likely among players with cognitive symptoms.

The comparison with earlier work shows why the correction is consequential. Science News reported on October 28, 2026, that the 2017 estimate of 99 percent was based on donated brains. Boston University School of Public Health said on October 28, 2026, that the new study builds on an August 2026 BMJ paper from the same group that put prevalence somewhere between 25 and 98 percent for players who died between 2016 and 2021. NBC News reported on October 28, 2026, that the August study estimated one-quarter of NFL players who died in a five-year span had CTE, while the new figure is three times higher.

The skeptical case is also part of the story. NBC News reported on October 28, 2026, that Dr. Jim Kelly, professor emeritus of neurology at the University of Colorado Anschutz, called the results estimates and noted that the researchers had no autopsies on five times as many players who died as they did have autopsies for. Kelly added that some autopsies may show only one or two lesions unlikely to cause behavioral change or dementia. The authors acknowledge that CTE can only be diagnosed after death and that their results apply only to deceased NFL players, not to living former players or to lower levels of play.

What this really means is that the public health question is no longer whether CTE is rare among former NFL players. The evidence points in the other direction. The uncertainty is about the exact share, the severity of disease in people who were never autopsied, and the degree to which CTE rather than other causes produced dementia. Tripodis told NBC News that he had to double-check the numbers and that because CTE cannot be diagnosed during life, the team was trying to estimate. He also said that much of the dementia can be from all causes, but that in this specific population it is very likely that CTE is causing dementia.

Why It Matters

The scale alone makes the finding hard to dismiss. The cohort covers 16 years of deaths and includes players whose brains were never examined. The average playing career in the group was 5.1 years, and 41.1 percent were 80 or older at death. The cohort was therefore not limited to players with unusually long careers.

The context from Boston University School of Public Health is equally important. The release notes that previous studies show NFL players develop dementia at four times the rate of the population, and that no other environmental or occupational exposure ever studied is known to have increased dementia risk at death by that much. It also quotes Matt Hasselbeck, an 18-year NFL veteran and ambassador for the DIAGNOSE CTE study, saying that it is hard to learn what the guys who built the game have suffered through and that the data must be used to make the game safer.

For the league, the study arrives alongside existing safety measures. NBC News reported on October 28, 2026, that the NFL has implemented redesigned helmets such as the Guardian Cap and the dynamic kickoff rule to lower collision speeds. An NFL spokesperson said in an emailed statement that the league continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts. The study does not evaluate those measures, and it cannot show whether they are working. It does provide a baseline against which future death records and brain bank data can be compared.

Next Up

The most immediate next step is diagnosis during life. Tripodis said in the Boston University release that discoveries from the brain bank have already brought the field significantly closer to a diagnosis during life, at which point the most important goal will be to develop effective treatments for CTE. Gallini said the estimate suggests a need to increase efforts to support families, diagnose CTE during life and treat CTE-related symptoms.

Surveillance will also matter. The authors caution that their results cannot be extended to living former players or to lower levels of play, and that all-cause dementia was estimated rather than CTE-caused dementia. Future work can test whether the same correction methods hold in other cohorts and whether prevention efforts change the trajectory. Tripodis told NBC News that reducing the number of brain injuries and brain impacts substantially decreases the risk. That prevention message is the clearest practical takeaway from a study built on deaths that occurred between 2008 and 2023.