Just how dangerous is American football? ~75% or more of recent, former NFL players most likely had CTE

Why not go back playing football without all that padding and helmets?

Apparently, the case number could be significantly higher. The researchers made a huge adjustment to correct for donor bias, but the size of this correction seems to be dubious. In addition, the researchers included also athletes who played only one or a few games.

Before the critical adjustment, 93% of donors had CTE.

"... in the last couple of decades, medical science has shined a light on one particularly risky aspect of the game: traumatic head injuries from the constant helmet clashes that increase the risk of a neurodegenerative condition known as chronic traumatic encephalopathy (CTE).

Currently, a CTE diagnosis can only be made after death. That’s because the condition’s characteristic lesions can only be revealed in thin slices of brain tissue. Imaging techniques developed for other kinds of neurodegenerative diseases fail to spot CTE, and blood tests cannot separate it from diseases like Alzheimer’s. ..."

Key points and abstract:

"Key Points

Question

After adjusting for selection bias, what is the prevalence of chronic traumatic encephalopathy (CTE) in deceased National Football League (NFL) players?

Findings

In this cross-sectional study of 2362 former NFL players who died between 2008 and 2023, 93.5% of players who were brain donors with neuropathologic evaluation had CTE. After adjustment for differential brain donation, the estimated prevalence of CTE neuropathology among all 2362 decedents was 74.5%.

Meaning

These findings suggest 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.

Abstract

Importance  The majority of knowledge regarding chronic traumatic encephalopathy (CTE) in National Football League (NFL) players is derived from autopsy-based studies on voluntarily donated brains. Because these cohorts are highly vulnerable to selection bias (specifically registry bias), population-level prevalence of CTE among former NFL players is unknown, limiting understanding of the impact of this disease.

Objective
To estimate the selection-bias adjusted prevalence of CTE neuropathology in deceased NFL players.

Design, Setting, and Participants
This population-based cross-sectional study used Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) brain bank data combined with National Death Index records on former NFL players. Both brain donor and nondonor NFL players who died between January 2008 and December 2023 were included. Data were analyzed from November 2025 to April 2026.

Exposure
Playing in at least 1 regular or postseason NFL game.

Main Outcomes and Measures

The main outcomes of this study were bias-adjusted prevalence of CTE neuropathology and all-cause dementia among the target population, both of which were measured in donors prior to this study. A cognitive symptom–related brain donation selection ratio (probability of donation given CTE divided by the probability of donation given no CTE) was estimated using Poisson regression and was applied to adjust donor-observed prevalence of CTE neuropathology at death and all-cause dementia during life. The prevalence estimates were adjusted for bias using the estimated selection ratio.

Results

The cohort consisted of 2362 deceased former NFL players (mean [SD] years played, 5.1 [3.9]; 971 [41.1%] aged ≥80 years at death), of whom 396 were brain donors and 1966 were nondonors.

Of 387 donors, 362 (93.5%) had CTE. The median selection ratio was 4.97 (95% CI, 4.72-5.26). 

Bias-adjusted population prevalence of CTE at death was 74.5% (95% CI, 69.6%-78.3%), with a conservative lower-bound analysis estimating 63.7% (57.2%-68.9%).

Bias-adjusted population prevalence of all-cause dementia history during life was 27.2% (95% CI, 22.6%-31.6%).

Conclusions and Relevance
The findings of this cross-sectional study suggest that selection bias materially inflates donor-based prevalence estimates but is unlikely to fully explain the high burden of CTE neuropathology among this population. Further research is required to understand the clinical impact of this disease."

ScienceAdviser

Bias-Adjusted Prevalence of Chronic Traumatic Encephalopathy Among Deceased National Football League Players (open access)