New study estimates nearly 75% of deceased former NFL players had CTE after researchers adjust for brain-donation bias

Nearly three-quarters of former NFL players who died between 2008 and 2023 are estimated to have had chronic traumatic encephalopathy, according to new peer-reviewed research that attempts to overcome one of the biggest limitations surrounding previous studies of the degenerative brain disease.

Researchers from Boston University, Mass General Brigham and the Concussion & CTE Foundation estimated a CTE prevalence of 74.5% among 2,362 former NFL players who died during the 16-year period. The study, published in JAMA Network Open, used statistical methods to account for the fact that families of former players with cognitive or behavioral symptoms are substantially more likely to donate their loved ones’ brains for research.

The new estimate is significantly lower than the extraordinarily high CTE rates observed directly among donated NFL brains, but researchers say it remains deeply concerning when compared with community brain banks, where CTE pathology has generally been detected in fewer than 1% of donors.

The findings do not mean three in four living NFL players currently have the disease, nor do they establish that every former player with CTE experienced symptoms. Researchers emphasized that CTE can still only be definitively diagnosed after death and that early-stage pathology may exist without producing severe cognitive or behavioral problems.

Researchers estimate 74.5% CTE prevalence after accounting for selection bias in donated brains

CTE research involving professional football has long faced an important statistical problem. Most confirmed cases come from athletes whose families voluntarily donated their brains after death, frequently because the individual had experienced memory problems, behavioral changes, depression or other symptoms that raised concerns about neurological disease.

That means donated brains are not necessarily representative of every former NFL player. Families of athletes without noticeable symptoms may be much less likely to participate in research, potentially making the raw proportion of CTE diagnoses among donated brains appear substantially higher than the true prevalence across the wider population.

The new study attempted to quantify and correct for that selection bias. Researchers examined 2,362 former NFL players who died between 2008 and 2023, including 396 whose brains were donated and 1,966 who did not participate in brain-donation programs.

Among 387 donated brains that received a neuropathological evaluation, 362, or 93.5%, showed evidence of CTE. Rather than treating that figure as representative of all former players, researchers examined differences between donors and non-donors and developed a statistical adjustment intended to estimate the disease’s prevalence across the entire deceased group. After applying that adjustment, the researchers arrived at an estimated CTE prevalence of 74.5%, with a confidence interval ranging from approximately 69.6% to 78.3%.

Former players with cognitive symptoms were far more likely to have brains donated for research

Researchers found strong evidence confirming why brain-donation studies can overstate disease prevalence if their samples are interpreted without adjustment. Former players who had clear cognitive symptoms before death were estimated to be almost five times more likely to have their brains donated than players without those symptoms.

Length of NFL careers also influenced participation. Brain donors had played an average of about 7.1 years in the league, compared with approximately 4.7 years among non-donors, while previous research has associated longer exposure to repetitive head impacts with greater CTE risk.

Researchers also examined factors including age at death, playing position, race, Pro Bowl appearances and Hall of Fame status. Those characteristics helped create a model estimating how likely different groups of former players were to become brain donors.

The approach is important because it moves the scientific debate beyond simply counting CTE cases in donated brains. The researchers acknowledge that the resulting 74.5% figure remains an estimate rather than a direct measurement, but argue that correcting for donation bias provides a substantially more realistic view of the potential burden among deceased professional football players.

Study includes more than 2,300 former NFL players who died over a 16-year period

The study analyzed former NFL players who died from 2008 through 2023 and had spent an average of approximately five years in the league. More than 40% of the overall group were at least 80 years old when they died, while the study also included younger former players across multiple generations of professional football.

Researchers used death certificates and information from the National Death Index to study players whose brains had not been donated. They examined records involving neurodegenerative disease and dementia before combining that information with the directly examined brain-donor group.

The researchers also estimated that approximately 27.2% of the full group had experienced dementia during life after accounting for selection bias. Dementia and CTE are not interchangeable conditions, however, and having CTE pathology does not automatically mean an individual developed dementia.

CTE refers to a specific pattern of abnormal tau protein accumulation in the brain associated with repetitive head impacts. Symptoms linked with the disease can include memory and thinking difficulties, behavioral or mood changes and, particularly in more advanced disease, dementia.

Findings do not mean 75% of living NFL players currently have CTE

Researchers have been particularly careful about what the new estimate does and does not establish. The 74.5% figure applies only to former NFL players who died during the study period, not to current athletes, living retirees, college players or people who participate in football recreationally.

The research also cannot establish the condition of an individual former player while that person is alive. At present, CTE requires examination of brain tissue after death for a definitive diagnosis, although researchers are working to identify biomarkers and other techniques that could eventually permit reliable diagnosis during life.

Some individuals may also have early-stage CTE pathology without developing noticeable symptoms. The presence of the characteristic brain changes therefore should not automatically be interpreted as proof that the disease caused a person’s behavioral problems, cognitive decline or death.

Those limitations are particularly important because fear surrounding CTE can itself affect former players and their families. Researchers argue that stronger estimates should be used to guide prevention, diagnosis and treatment rather than encourage living athletes to assume they already have an incurable neurological condition.

New research significantly narrows uncertainty from earlier NFL CTE study

The findings build on an earlier 2026 analysis by researchers from the same group that attempted to quantify CTE prevalence among former NFL players who died between 2016 and 2021. That study produced an extraordinarily broad estimated range of roughly 25% to 98%, reflecting major uncertainty about the extent to which brain-donation bias affected the results.

The new research uses additional information about donors and non-donors to make a more specific estimate. By identifying characteristics associated with donation and incorporating those differences mathematically, researchers were able to narrow the estimated prevalence to approximately three-quarters of the deceased-player population studied.

The adjusted figure remains remarkably high compared with community brain banks. Boston University researchers say CTE has consistently been detected in fewer than 1% of donors in large community brain-bank samples from countries including the United States, Australia, Austria and Brazil.

That contrast strengthens the evidence that substantial exposure to repetitive head impacts is associated with much higher CTE risk. It does not mean every football player will develop the disease, but researchers say professional football represents an occupational environment where repeated head impacts can accumulate over many years.

Repetitive head impacts matter even when they do not cause diagnosed concussions

The scientific understanding of CTE has increasingly shifted away from focusing solely on diagnosed concussions. Researchers now emphasize cumulative exposure to repetitive head impacts, including blows that may not cause immediate symptoms or qualify clinically as concussions.

An NFL player can experience hundreds or thousands of impacts during practices and games over a career. Linemen in particular may sustain frequent lower-intensity collisions on nearly every play even when those hits do not produce obvious injuries.

That distinction has implications for prevention. Improving concussion diagnosis remains important, but preventing CTE may also require reducing the overall number and intensity of head impacts athletes experience throughout their playing careers.

Football organizations have already modified practice rules, kickoff structures, tackling techniques and helmet technology in an effort to reduce head trauma. Researchers say future studies will be necessary to determine whether those changes meaningfully reduce CTE prevalence among younger generations of players.

Because many people included in the new study played decades ago, the results cannot establish the CTE risk faced by athletes entering the NFL under current rules and equipment standards.

NFL safety debate is likely to intensify after latest CTE estimate

The findings are likely to renew scrutiny of whether professional football has done enough to reduce repetitive brain trauma. The NFL has introduced numerous safety changes over the past two decades, including updated concussion protocols, restrictions on certain types of contact and continuing investment in helmet technology.

The league has said it remains committed to reducing concussions and head impacts while expanding health and mental-wellness resources for current and former players. The challenge is determining whether those interventions significantly alter the long-term neurological risk associated with years of professional football.

That answer will take time because CTE can develop over decades. Players competing under newer safety rules may need to be followed for many years before researchers can determine whether disease prevalence declines compared with generations represented in the latest study.

The findings could also influence decisions beyond professional football. Researchers have increasingly examined whether delaying the age at which children begin tackle football, limiting full-contact practices and monitoring cumulative impacts could reduce long-term neurological risk.

Researchers say diagnosing CTE during life is the next major scientific challenge

One of the most important unanswered questions is whether scientists can develop a reliable method to identify CTE before death. A validated living diagnosis would transform both research and treatment because doctors could follow patients over time rather than relying primarily on postmortem examinations.

Researchers are studying blood biomarkers, brain imaging and other techniques that may eventually distinguish CTE from Alzheimer’s disease, other forms of dementia and mental-health conditions with overlapping symptoms.

A living diagnosis could also allow researchers to test potential treatments directly. At present, doctors can treat symptoms such as depression, anxiety, sleep disorders or cognitive problems, but there is no established therapy that specifically reverses CTE pathology.

The new prevalence estimate therefore provides a clearer picture of the potential size of the problem while underscoring how much remains unknown. Researchers now have stronger evidence that CTE may have been widespread among deceased NFL players, but prevention, diagnosis during life and disease-specific treatment remain major scientific challenges.

Key takeaways from the new CTE study of former NFL players

• Researchers estimate 74.5% of NFL players who died between 2008 and 2023 had CTE neuropathology after adjusting for brain-donation bias.
• The study analyzed 2,362 deceased former NFL players, including 396 brain donors and 1,966 non-donors.
• Among donated brains with neuropathological evaluations, 93.5% showed CTE, but researchers concluded that raw figure was inflated by selection bias.
• Former players with clear cognitive symptoms were nearly five times more likely to have their brains donated for research.
• The estimate applies only to deceased former NFL players and cannot determine how common CTE is among living or active players.
• CTE can currently be definitively diagnosed only after death, and some people with early-stage pathology may never develop significant symptoms.
• Researchers estimate approximately 27% of the deceased-player population also experienced dementia during life.
• The findings are expected to intensify efforts to reduce repetitive head impacts and develop methods to diagnose and treat CTE during life.