Study finds CTE in at least quarter of deceased NFL players

At least one in four former NFL players who died from 2016 through 2021 had chronic traumatic encephalopathy, according to a new study that researchers say offers a clearer baseline for how common the degenerative brain disease may be among retired professional football players.

The study, released Tuesday and published in The BMJ, examined former players who appeared in at least one NFL game and died during that six-year period. Researchers from Mass General Brigham, Boston University and the Concussion + CTE Foundation found that 235 of 878 players who died in that span had donated their brains for study, and 215 of those donated brains were diagnosed with CTE. That means at least 25% of all former NFL players who died during the period had the disease.

“We’ve known that this disease process can be caused by, in part, repeated traumatic brain injury. But we didn’t know how common it was,” said Dr. Daniel Daneshvar, the study’s lead author and chair of physical medicine and rehabilitation at Mass General Brigham.

CTE is associated with repeated blows to the head, including concussions, and can only be definitively diagnosed after death through examination of brain tissue. Symptoms linked to the disease include problems with attention and memory, dementia, mood disorders and headaches.

Because CTE can be diagnosed only after death, much of the existing research has relied on brains donated by families or by people who experienced symptoms in life. That has made it difficult to estimate the disease’s true prevalence. The new study used the UNITE Brain Bank at Boston University, where more than 330 brains of NFL players who died between 2008 and 2021 have been donated; 93% of those brains have been diagnosed with CTE, NPR reported.

To build a broader denominator, researchers created a list of every player who appeared in at least one NFL game since 1949, reviewed demographic information and obtained death certificates from the Centers for Disease Control and Prevention. They then focused on 2016 to 2021, when the proportion of brain donations was highest.

Daneshvar said the 25% figure is at the “low end.” NPR reported that the study noted additional CTE diagnoses outside the brain bank sample, suspected cases in players whose brains were not examined and 215 death certificates for non-donors that listed a neurodegenerative disease as a cause of death. At the highest possible estimate, if all former players were assumed to have CTE except 20 whose brains were definitively cleared, prevalence would be about 97%.

“The true rate of CTE at death in NFL players is somewhere in the middle,” Daneshvar said.

An NFL spokesperson said the league “continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts.” The spokesperson added that the NFL is committed to providing “a robust — and expanding — set of resources” for former players’ physical and mental well-being and encourages them to seek care when concerned about their health.

The study also examined dementia. Researchers found that more than 90% of brains with Stage IV CTE, the most advanced stage, were associated with a dementia diagnosis made by clinicians using medical records and information from loved ones. The link was less clear at lower CTE stages; NPR reported that about 40% of samples without CTE were also associated with dementia.

Rachel Grashow, a neuroepidemiologist at Harvard T.H. Chan School of Public Health who was not involved in the research, said living former players should discuss concerning symptoms with doctors and loved ones. She said conditions common among former NFL players, including sleep apnea, high blood pressure and low testosterone, can produce symptoms associated with CTE but may be treatable.

“Our concern is that the public and kitchen table conversations around CTE are creating hopelessness in living former NFL players,” Grashow said.

Daneshvar said repeated traumatic brain injuries are known to contribute to elevated neurodegenerative disease rates, and that NFL players have about four times the rate of death from neurodegenerative disease as the general population. He said many impacts occur before players reach the NFL.

“The bulk of the head impacts that these former NFL players experienced didn’t occur at the NFL level,” he said. “They occurred at the collegiate level… and at the high school level and in many cases the youth level.”