Editor's note: This popular story from the Daily Briefing's archives was republished on Feb. 9, 2024.
By Ben Palmer, Senior Staff Writer
The National Football League, like other major sports leagues, has had a challenging year adapting to the new coronavirus. But while all eyes have been on teams' adjustments to curb the spread of Covid-19, there's been less emphasis on chronic traumatic encephalopathy (CTE): a rare and little understood brain disease that previously was a growing focus for researchers—and the public—before the pandemic.
CTE has become almost synonymous with professional football. The brain disease is believed to cause deterioration of brain matter and the abnormal accumulation of tau, a protein found in brain cells, in the brain.
Currently, CTE can only be diagnosed post-mortem by examining the brain tissue of deceased subjects. However, scientists believe that people who are diagnosed with the disease post-mortem can present with symptoms while they are living—such as aggression, anxiety, confusion, dementia, depression, memory loss, and substance misuse—that could serve as indicators of the disease. There is no known treatment for the disease.
While the exact cause of CTE remains unclear, many scientists theorize that it stems from repeated head trauma, and as such, much of the research done into CTE has focused on contact sports players, such as football and hockey athletes, as well as military servicemembers who've served in war zones.
For example, a study published in JAMA in 2017 looked at 202 brains from deceased football players, some from the NFL and some from the Canadian Football League (CFL), as well as semiprofessional athletes and athletes who had not gone professional but played football in college or high school.
The researchers found "clear evidence" of CTE present in 87.6%, or 177, of the brains examined. On average, those 177 athletes had played football for 15 years, the researchers said. Among the different groups of players diagnosed with CTE, 110 of 111 former NFL players had the disease, as did seven of eight former CFL players.
The researchers also classified the brains with evidence of CTE as having either "mild" or "severe" pathology. They found that 133 of the 177 CTE cases identified had severe pathology while 44 had mild pathology.
Cause of death was also assessed by the researchers, who found that the most common cause of death among those with mild CTE was suicide, representing 27% of cases, while degenerative brain diseases like Alzheimer's and Parkinson's were the most common causes of death for those with severe CTE, accounting for 47% of fatalities.
While researchers do not know exactly what causes CTE, experts say that repeated concussions and even less severe hits to the head can result in permanent changes to the structure of the brain. According to Philip Bayly, an engineering professor at Washington University in St. Louis, "The pain you feel [after a hit] is not necessarily an indicator of the damage that does to your head."
The NFL keeps track of injuries that occur in both practice and games in-season as well as during the preseason. While their data doesn't include hits to the head that don't rise to the level of a concussion, the NFL's data shows that concussions are very common in the league, with 224 total concussions recorded last year.
While football is only one of several contact sports associated with CTE, it's become a key area of focus for researchers and advocates because of the number of former NFL players who have committed suicide and were found to have the condition.
Perhaps one of the most notable cases was former Miami Dolphins linebacker Junior Seau, who committed suicide in May 2012 and was later found to have CTE at the time of his death. But Seau is certainly not the only case:
And while CTE cannot be diagnosed in individuals who are still living, former football players increasingly are making connections between the disease and symptoms—such as confusion, memory loss, and anxiety—that they experience in their post-football life.
For instance, T.J. Abraham played football in high school and then at Duquesne University for three years. Abraham never played in the NFL, and instead, went on to become an obstetrician-gynecologist at UPMC Magee-Womens Hospital.
But at age 42, Abraham had to end his career after he was diagnosed with neurodegenerative dementia, which caused scores of memory problems for Abraham. His doctors agreed that football was likely the source of his problems and said there was a strong possibility he suffered from CTE.
Former Baltimore Ravens and Cleveland Browns running back Jamal Lewis also has spoken about his post-career struggles. In an interview with Bleacher Report in 2018, Lewis said he's experienced 10 concussions as a result of playing football and became unconscious "two or three" times.
Since retiring from football, Lewis said it's very common for him to start his car, start driving, and forget where he's going. "It's a normal thing," he said. "Like, Where am I at?"
Lewis also said he experiences sensitivity to light, commonly has headaches, and suffers from "moments" of depression, sinking into a blank "sadness" about twice a week. He also acknowledged that his temper has become more unpredictable.
Former Denver Broncos tight end Nate Jackson in June described the frustration that former football players experience when they struggle in their daily lives but can't get a clear diagnoses.
"I have heard the letters 'C,' 'T,' and 'E' so many … times, the question becomes: When I am struggling in the 'real world,' is it because I am conditioned for a different reality? Or because I actually have brain damage?" he wrote. "Nobody knows, because frustration can be read as dementia."
The inability to diagnose the condition in life also makes it difficult to know CTE's prevalence.
In 2018, epidemiologists Zachary Binney and Kathleen Bachynski attempted to estimate how prevalent the disease is in former NFL players using the July 2017 JAMA study, which found that 99% of former NFL players had CTE post-mortem. Based on their calculations, Binney estimated that the prevalence of CTE among the 1,142 former NFL players who died between February 2008 and May 2016 could be as high as 30% or as low as 10%.
"I'm reasonably confident that it's somewhere north of 10%, and I would not at all be surprised—and indeed it's my best guess right now—that the prevalence is probably more in the 20 to 30% range," Binney said.
But for current players, those estimates could be lower, according to Bhramar Mukherjee, a biostatistician at the University of Michigan's School of Public Health. "The probability of developing CTE could be changing over time, because the protective gear and style of play is changing over time," he said.
One way in which the protective gear is changing is new helmets. In a paper published in October 2019, a group of scientists led by David Camarillo, a bioengineer, developed and tested a new helmet that features liquid shock absorbers. They estimated the helmet could reduce concussions by at least 75%.
The new helmet has yet to be tested on the field, however, and some critics like Lee Goldstein, a psychiatrist and researcher at the CTE Center at Boston University, have said that reducing concussions won't help prevent CTE.
"I can say with great certainty that there is no correlation between a single concussion and CTE," Goldstein said. "It's the accumulation of hits."
But Camarillo believes that if the new helmet reduces concussions, it also should reduce the force of any other hits that could cause long-term brain damage.
"I hope this is like the seatbelt," Camarillo said. "And the day will come when you think it's just crazy we didn't have it sooner."
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