Digital illustration of a football helmet revealing brain damage, symbolizing the risk of CTE in football.

CTE in NFL Players: Unpacking the Prevalence and Risks

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Nico Varela in Health & Wellness November 2026 • 3 min read.

"A closer look at new data on chronic traumatic encephalopathy among former football players and what it means for the future of the sport."


In July 2017, a study published in JAMA revealed that 110 out of 111 deceased NFL players (99%) showed neuropathological evidence of chronic traumatic encephalopathy (CTE). This progressive neurodegenerative disease, linked to repeated head trauma, sparked widespread concern and media attention.

However, diagnosing CTE is currently only possible post-mortem, raising questions about the representativeness of these findings. Players exhibiting CTE symptoms may be more inclined to donate their brains for research, potentially skewing prevalence estimates. The original study acknowledged this selection bias but didn't quantify its impact.

This article explores new research published in Neurology, which re-examines the JAMA study's data to provide a more nuanced understanding of CTE prevalence in former NFL players. By accounting for potential selection bias, this analysis offers a broader perspective on the risks associated with professional football.

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CTE’s Potential Impact

CTE is a serious brain condition associated with repeated head impacts, but its prevalence among NFL players remains difficult to establish with certainty. Researchers continue to distinguish between documented disease, suspected cases, and symptoms that may have multiple causes. The potential consequences can include changes in mood, behavior, thinking, and long-term functioning.

Understanding CTE

Harvard Health, Cleveland Clinic, and other medical references describe CTE as a brain disease or condition linked to repeated head injuries. Reported symptoms may include behavioral and mood problems as well as difficulties with thinking, and the condition may worsen over time. Diagnosis and staging remain challenging because CTE is generally identified through examination of brain tissue after death rather than through a definitive routine test during life.

Foundations of CTE Research

The Concussion & CTE Foundation describes CTE as a degenerative brain disease caused in part by repeated traumatic brain injuries. These injuries can include diagnosed concussions as well as nonconcussive impacts. This framing helped broaden attention beyond single, obvious concussions to the cumulative effects of repeated head trauma.

Estimating CTE: Methods and Challenges

Digital illustration of a football helmet revealing brain damage, symbolizing the risk of CTE in football.

The recent analysis utilizes data from a cohort of 1,142 deceased NFL players who were eligible to participate in the original CTE study. The researchers focused on addressing the selection effect, acknowledging that not all players are equally likely to donate their brains. They highlight the importance of considering this bias when interpreting CTE prevalence.

Correcting for this selection effect requires estimating the probability of brain donation among players with and without CTE. The analysis uses two key parameters:

  • The probability that a player with CTE donates their brain.
  • The ratio of donation probabilities between players with and without CTE.
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An Evolving Evidence Base

Research on CTE is still developing, and current findings do not provide a complete picture of how often the disease occurs in NFL players. Studies must account for differences in exposure, symptoms, brain examination, and research methods. As a result, conclusions about prevalence and risk should be treated as provisional rather than definitive.

Limits of Current Evidence

A major limitation in CTE research is that symptoms associated with the condition are not necessarily unique to CTE. Retrospective studies and brain donations can also produce selection concerns, because participants may not represent all former NFL players. These limitations make it difficult to translate documented cases directly into a population-wide prevalence estimate.

Comparing Risk and Uncertainty

NFL players experience repeated head impacts, but individual exposure and outcomes can vary substantially by position, career length, playing style, and other factors. Comparisons between athletes and nonathletes therefore require careful attention to differences in both exposure and follow-up. Available evidence supports concern about repeated trauma while leaving the precise level of risk uncertain.

By varying these parameters, the researchers generated a range of plausible CTE prevalence estimates. The findings emphasize that the commonly cited 99% figure might be an overestimation due to selection bias.

Interpreting the Results: What Does This Mean for Football?

The analysis provides a more realistic range of CTE prevalence among deceased NFL players. While the exact number remains uncertain, the study underscores the importance of accounting for selection bias in research. These findings can inform discussions about player safety, rule changes, and long-term health management in professional football. Future research, including the development of in vivo CTE biomarkers, will further refine our understanding of this complex issue.

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A Cautious Synthesis

The evidence supports an association between repeated head trauma and the possibility of CTE, but it does not establish that every player with repeated impacts will develop the disease. Symptoms and long-term outcomes can differ widely among individuals. A balanced interpretation therefore recognizes both the seriousness of the potential harm and the limits of current diagnostic and prevalence estimates.

The Next Research Questions

Future work will need to improve the ability to identify CTE during life and clarify how repeated impacts relate to later neurological outcomes. Researchers also need more representative participants and consistent methods for measuring exposure and symptoms. Progress in these areas could make risk estimates more reliable and support better prevention and care.

Challenges Beyond the Diagnosis

CTE research exists within broader challenges involving player safety, medical decision-making, and the long-term consequences of professional football. The uncertainty surrounding diagnosis can complicate communication among players, families, clinicians, researchers, and sports organizations. Addressing these challenges requires both stronger evidence and sustained attention to prevention and support.

Players and Families

For players and families, concerns about CTE extend beyond a research statistic to questions about memory, mood, behavior, independence, and future health. Symptoms associated with brain injury can affect relationships and daily life even when the underlying cause is uncertain. Clear communication, careful evaluation, and appropriate support remain important while research continues.

About this Article -

Written with AI assistance from published research, and reviewed by the Mystum team. See our About page for more information.

Everything You Need To Know

1

What is CTE, and why is it a concern for NFL players?

CTE, or chronic traumatic encephalopathy, is a progressive neurodegenerative disease linked to repeated head trauma. In the context of NFL players, this is particularly concerning due to the high-impact nature of the sport, which exposes players to frequent head injuries. CTE can lead to various neurological and psychological symptoms, affecting the long-term health and well-being of former players. Diagnosing CTE is only possible post-mortem, which complicates the understanding of its prevalence and impact.

2

How was the initial prevalence of CTE determined among NFL players, and what were the key findings?

A study published in JAMA in July 2017 revealed that 110 out of 111 deceased NFL players (99%) showed neuropathological evidence of CTE. This finding, highlighting a very high prevalence, sparked significant concern and media attention. However, the study acknowledged potential selection bias, recognizing that players with CTE symptoms might be more likely to donate their brains for research, which could skew the prevalence estimates.

3

What is selection bias in the context of CTE research, and how does it affect the interpretation of findings?

Selection bias refers to the systematic error introduced when the sample studied is not representative of the entire population. In CTE research, it arises because players exhibiting symptoms of CTE may be more inclined to donate their brains for research. This means that the sample of brains examined might have a higher proportion of individuals with CTE than the overall population of deceased NFL players. Consequently, the initial 99% figure might be an overestimation due to this bias, making it critical to account for it in the research.

4

What methods are used to estimate CTE prevalence while accounting for selection bias?

The recent analysis in Neurology re-examines the JAMA study's data to provide a more nuanced understanding of CTE prevalence in former NFL players. The research utilizes data from a cohort of 1,142 deceased NFL players who were eligible to participate in the original CTE study. The analysis employs two key parameters to correct for selection bias: * The probability that a player with CTE donates their brain. * The ratio of donation probabilities between players with and without CTE. By varying these parameters, researchers generate a range of plausible CTE prevalence estimates, providing a more realistic view of the risks.

5

What are the implications of this research for the future of football and player safety?

The findings provide a more realistic range of CTE prevalence among deceased NFL players, emphasizing the importance of accounting for selection bias in research. This understanding can inform discussions about player safety, rule changes, and long-term health management within professional football. The study highlights the need for a nuanced approach to the issue, acknowledging that the exact prevalence remains uncertain. Future research, including the development of in vivo CTE biomarkers, will further refine our understanding of this complex issue, paving the way for improved player safety measures and healthcare strategies.

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