NFL football player helmet
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About three in four former NFL players who died between 2008 and 2023 had chronic traumatic encephalopathy, or CTE, according to a new estimate from Boston University researchers. The study, published in JAMA Network Open, puts the figure at 74.5%, far above the less than 1% found in community brain banks.
The number is lower than the eye-catching 99% from a 2017 study — but it may be more meaningful. For the first time, researchers estimated CTE across all deceased former NFL players in the period, including the many whose brains were never examined.
A Disease Written in Brain Tissue
CTE is a degenerative brain disease linked to repeated blows to the head. It involves a buildup of an abnormal form of tau protein that damages brain tissue and can kill brain cells. It can only be diagnosed after death, by examining brain tissue under a microscope.
That limitation shapes everything about CTE research — scientists can only study brains that families choose to donate. Yorghos Tripodis, a Boston University biostatistician and study author, told NBC Boston that helmets protect the skull but do not do enough against the rotational forces that move the brain within it.
The Selection-Bias Problem Behind the 99% Figure
In 2017, Boston University researchers reported CTE in 110 of 111 former NFL players whose brains were donated, about 99%. The authors said at the time that the results could not be used to estimate prevalence. Families who saw memory loss, mood changes, or behavior problems in a loved one were more likely to donate, which skews brain bank samples toward people with symptoms.
The new study tackles that bias directly. Researchers used federal death records to identify all 2,362 former NFL players who died during the 16-year window. Of the 387 donated brains examined, 362, or about 94%, showed some stage of CTE.
The team estimated that families of players with cognitive symptoms were about five times more likely to donate. They then used that selection ratio to adjust the 94% donor rate to the population-wide figure of 74.5%, the Associated Press reported. Under their most conservative assumptions, the estimate was 63.7%.
An earlier study from the same research community, released in August, could only say the rate was somewhere between about 25% and 98% for players who died from 2016 to 2021. The new method narrows that range sharply.
A Diagnosis Is Not a Destiny
The authors stress what the figure does not mean. It applies only to deceased former NFL players and does not predict how many living or active players have CTE. Having CTE pathology at death is also not the same as having dementia.
Boston University has said that not every player with CTE pathology develops symptoms, especially at early stages. The researchers separately estimated that 27.2% of the former players had dementia during their lives, a figure they said likely understates the true rate, according to ABC News.
"With CTE consistently found in less than 1% of donors to community brain banks, an estimated 75% prevalence among NFL players who died over a 16-year period is concerning," said lead author Julia Gallini, a doctoral candidate in biostatistics at Boston University. She said the finding points to a need to support families, diagnose CTE during life and treat related symptoms.
Daniel Daneshvar, a Harvard Medical School neuroscientist and co-author, said care can still help. Treatment has improved symptoms and quality of life for some former players, particularly in midlife, "while we cannot yet treat the underlying CTE pathology," he said, according to ScienceAlert.
Youth Players Are the Next Question
The study covers only the highest level of play. Most Americans who play tackle football never reach college or the pros, and Tripodis noted that more than 20 million men alive in the U.S. today have played the sport.
The authors want to estimate CTE rates among high school and college players next, though they caution that limited data may make that difficult. Previous Boston University work found CTE in some young athletes who died before age 30, most of them amateurs, so the question is not academic.
Tripodis said the biggest lever is reducing exposure early. "If we could reduce tackle football before high school, or not have tackle football during practice at all levels, as it is happening in NFL, then we will reduce the main cause of the disease," he told NBC Boston.
The league acknowledged a link between football and CTE in 2016 and has since changed rules and equipment, including padded Guardian Caps worn over helmets in practice. Tripodis said such equipment protects the skull, but rotational forces inside the head remain the core problem.
The NFL said it continuously works to make the game safer, including by reducing concussions and head impacts. The NFL Players Association called studies like this critical to understanding football's long-term effects.
For families, the practical steps are measured. Former players with memory, mood or behavior changes should talk with a doctor, since some symptoms can be treated even if CTE itself cannot. Parents weighing youth tackle football can ask coaches how often players take full-contact hits in practice.
The finding does not mean three-quarters of players will develop dementia. It does suggest that repeated head impacts at the professional level leave a mark on the brain far more often than in the general public. Researchers say a test to diagnose CTE in living people remains the most important missing tool.
What Readers Want to Know
What did the new CTE study find? It estimated that 74.5% of former NFL players who died between 2008 and 2023 had CTE at death.
Why is this lower than the 99% figure from 2017? The 2017 study looked only at donated brains, which over-represent players with symptoms. The new study adjusted for that bias.
Does this mean 75% of players will get dementia? No. CTE pathology at death is not the same as dementia. The researchers separately estimated about 27% had dementia during life.
Can CTE be diagnosed in living people? Not yet. It can only be confirmed by examining brain tissue after death.
Does this apply to current or youth players? No. The estimate covers only deceased former NFL players. Researchers want to study high school and college players next.
What should former players with symptoms do? Talk with a doctor. Some symptoms of memory, mood, and behavior problems can be treated.
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