- Statistical modeling estimated CTE in 74.5% of former NFL players who died from 2008 through 2023.
- The model adjusted for selective donation and was based on a sample of 387 NFL brain donors.
- The estimates excluded living players, CTE stage, and other types of athletes.
A statistical model that extrapolated data from deceased National Football League (NFL) brain donors to include all former NFL players who died from 2008 through 2023 estimated that nearly three in four had chronic traumatic encephalopathy (CTE).
Yorghos Tripodis, PhD, of the Boston University School of Public Health, and colleagues developed the model by quantifying cognitive symptoms of NFL brain donors who had CTE assessments. CTE can be identified only through autopsy.
After adjusting for bias associated with brain donation, the model estimated the prevalence of CTE at death was 74.5% (95% CI 69.6-78.3) for all former NFL players who died from 2008 through 2023, Tripodis and colleagues reported in JAMA Network Open.
The analysis incorporated a selection ratio to estimate the prevalence of CTE. The ratio assumed that brain donation was driven primarily by family members observing cognitive symptoms in former NFL players.
“This is an interesting attempt to statistically account for the problem of selective donation into a brain bank so that they can estimate the prevalence of CTE among all NFL players who died during the time interval they were looking at when they only could analyze a subset of them,” observed Marc Weisskopf, PhD, ScD, of the Harvard T.H. Chan School of Public Health in Boston, who wasn’t involved with the study.
The numbers don’t necessarily apply to all NFL players, he pointed out. “The deaths they are working with are about 10% of all that could have occurred in that period, and there are reasons to suspect CTE would be less common among the still-living players when they eventually die,” Weisskopf told MedPage Today.
“The statistical approach is sound, although it’s important to realize that it is very dependent on some assumptions — notably that brain donation is entirely driven by cognitive symptoms and that those are captured by dementia on the death certificate and their adjustment for additional mild cognitive impairment,” he said.
CTE has four distinct stages, with higher CTE stages correlating with more severe cognitive symptoms. “Even if we were able to determine an unbiased estimate of the proportion of living and deceased players with CTE, we still don’t have information on their probable CTE stage, which has the most meaning for their everyday lives and health,” noted Rachel Grashow, PhD, MS, also of Harvard, who also wasn’t involved with the study.
The study findings do not apply to other groups, observed Julie Stamm, PhD, of the University of Wisconsin-Madison, who wasn’t part of the study. “It does not provide an estimate of CTE among athletes in other sports or at lower levels of play,” Stamm told MedPage Today.
“Greater lifetime repetitive head impact exposure has been linked to an increased risk of developing CTE, so it is likely that the prevalence would be higher among NFL players than those who played at lower levels,” she added. “However, we cannot estimate the prevalence among players at lower levels at this time.”
Tripodis and colleagues used UNITE brain bank data and national death index records to evaluate former NFL players who died from 2008 through 2023. The mean duration of play was 5.1 years and 41.1% of deceased players were ages 80 or older when they died.
Of 2,362 deceased former NFL players, 396 were brain donors and 1,966 were nondonors. Of 387 donors, 362 (93.5%) had CTE at autopsy. The estimated prevalence of all-cause dementia was 27.2% (95% CI 22.6-31.6).
The median selection ratio was 4.97 (95% CI 4.72-5.26), meaning that former players with cognitive symptoms were five times more likely to have their brains donated by their family than those without these symptoms.
“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,” Tripodis and co-authors stated.
Studies like this can refocus attention to the “20,000 living former NFL players, some of whom are suffering with cognitive symptoms or have been diagnosed with dementia,” Grashow told MedPage Today. The Football Players Health Study at Harvard has more than 5,000 former players in its cohort, she noted.
“In our conversations with and ongoing study of these NFL players, we’ve found that head injury increases risk for treatable conditions that — if left untreated — increases risk for cognitive issues and dementia. These include sleep apnea, high blood pressure, low testosterone, depression, anxiety, tinnitus, and more,” she added.
“So, if we are thinking about how these recent findings relate to the many thousands of former living players, the story shifts to one of surveilling and treating former players for treatable conditions so we can reduce their dementia and heart disease risk,” Grashow said. “This, we believe, is one of the best ways we can tackle the potential symptoms, risks, and challenges of CTE right now — before we turn to estimating prevalence, which is at the end of life.”
