A new study from Boston University The estimate that nearly 75 percent of NFL players who died over a 15-year period had signs of CTE in the brain raises concerns, and experts say it demonstrates the need to collect more data on the disease.
CTE, or chronic traumatic encephalopathy, is a degenerative brain disease found in people who have suffered repeated blows to the head. It can only be definitively diagnosed after death. It was also found in the brain of other athletesfirst responders and military personnel, but is rarely seen in the general population.
The Boston University research builds on data published in the British Medical Journal in August. This data estimated that somewhere between 25% 98% of former NFL players who died between 2016 and 2021 had CTE. The overall estimate reflects uncertainty about the representativeness of the brain donors studied relative to the overall NFL population, as brain donors are more likely to present with symptoms believed to be related to CTE.
The Boston researchers looked for signs of the disease in the brains donated by 387 players who died between 2008 and 2023 – a subset of the 2,362 former NFL players who died during that period. Ninety-four percent of donors had some form of CTE. Researchers estimated that former NFL players with cognitive symptoms were 5 times more likely than others to donate their brains to science, and estimated from this that 74.5% of players suffered from some form of CTE. The research is published in JAMA Network Open.
CBS News Chief Medical Correspondent Dr. Jon LaPook cautioned that figure may be an overestimate. He noted that the research looked at how many former players had signs of CTE in their brains — not how many had actual CTE symptoms.
Dr. Kristen Dams-O’Connor, Director of the Mount Sinai Brain Injury Research Center, said the paper’s findings “cannot and should not be interpreted as being representative of current living athletes.” She pointed out that of those whose brains have been studied, “many… have ended their careers a long time ago.” In recent years, the NFL has implemented rule changes aimed at reducing on-field concussions and introduced more protective equipment, including Goalkeeper caps.
“This should translate into lower CTE risk among recent generations of gamers, compared to those who played decades ago,” Dams-O’Connor said.
The NFL told CBS News in a statement that it is “continually working to make football safer, including implementing strategies to reduce concussions and head impacts.”
Dams-O’Connor said that while Boston University used “robust methods” to adjust for selection bias in the data, there are still other gaps, such as accounting for the approximately 20,000 NFL players who could have died during the 15 years of the study but did not die. She also said the findings could not be applied to “the vast majority of people who played youth soccer” or other non-professional contact sports.
“It’s a useful study to try to see the bigger picture, recognizing that those who donate their brains are more likely to have cognitive symptoms and are often more likely to have experienced changes,” said Dr. Jeremy Tanner, assistant professor of neurology at the Glenn Biggs Institute for Alzheimer’s and Neurological Disorders at UT San Antonio Health Sciences Center. “Even accounting for this selection bias, when you look more broadly it’s at least between 20 and 25 percent, which is telling and really shows the need to advance research.”
CTE research in its “silent phase”
Dr. Jay Alberts, director of the Cleveland Clinic Concussion Center, said the data shows the need to look for warning signs of CTE.
“We often think of neurological diseases, including CTE, as having a silent phase. These things change and we can’t detect them,” Alberts said. “But I don’t think it’s silent per se. I think what we need to do is listen more carefully and use better metrics to understand what these changes are.”
These measures could include studying a person’s “instrumental activities of daily living,” or IADL, Alberts said. This includes skills such as driving a car or balancing a checkbook, where a person must use cognitive and motor functions simultaneously. In patients with Alzheimer’s or Parkinson’s disease, IADL begins to change between five and seven years before a diagnosis is made. He said CTE could be similar.
“These types of activities really provide insight into how the brain works, and I would argue that these are things that would help us listen more effectively,” he said.
Finding other signs of CTE
Understanding how a person’s brain function may change during the early stages of CTE could make diagnosis easier, Alberts said. It could also lead to interventions that could “slow it down, or even reverse it.”
Alberts and Tanner also highlighted research investigating whether there are biomarker changes that could be linked to CTE. Ongoing studies, including one that has a study site at UT Health San Antonio, follow current or former players throughout their lives to see if there are any abnormal changes in the body or brain over the years. Alberts called for even more long-term research, and Tanner said such studies can benefit more than just former NFL players.
“This has really been an area of rapid scientific progress over the last 10 to 20 years, and has led to breakthroughs in new therapies for Alzheimer’s disease and hopefully many other neurodegenerative diseases like CTE, Lewy body disease and others in the years to come,” Tanner said.
“We hope to be able to develop tools and biomarkers to detect these brain changes across the lifespan, which will allow us to study these diseases across the lifespan and, ideally, learn ways to better prevent or treat these diseases.”
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