The NFL logo is surrounded by helmets of the 32 teams in the league. A new survey released Monday found that a third of former NFL players believe they have CTE, a degenerative brain disease linked to concussions.

The NFL logo is surrounded by helmets of the 32 teams in the league. A new survey released Monday found that a third of former NFL players believe they have CTE, a degenerative brain disease linked to concussions. / Getty Images

One-third of former professional football players reported in a new survey that they believe they have the degenerative brain disease known as chronic traumatic encephalopathy, or CTE.

The research, published Monday in the medical journal JAMA Neurology, represents one of the broadest surveys to date of former NFL players' perception of their cognitive health and how widely they report symptoms linked to CTE, which is thought to be caused by concussions and repeated hits to the head.

The findings are based on a Harvard University survey of retired professional football players whose careers spanned from 1960 and 2020. Of the 1,980 respondents, 681 said they believed they had CTE. More than 230 former players said they had experienced suicidal thoughts, and 176 reported a diagnosis of Alzheimer's disease or other form of dementia.

Some symptoms — including depression, signs of cognitive impairment and suicidal thoughts — were more common among the "perceived CTE" group, researchers found. Even after controlling for other predictors of suicidality, the study found that retired players who believed they had CTE were twice as likely to report frequent thoughts of suicide or self-harm.

But the inability to diagnose CTE in living patients meant researchers were unable to determine when former players' symptoms were a result of CTE or other causes. If other causes were responsible, researchers warned, even the belief of having CTE — an incurable degenerative brain condition — could lead to symptoms like depression.

"A key takeaway from this study is that many conditions common to former NFL players such as sleep apnea, low testosterone, high blood pressure and chronic pain can cause problems with thinking, memory and concentration," Rachel Grashow, a neuroscientist at Harvard and the lead author on the study, said in a press release.

"While we wait for advances in CTE research to better address living players’ experiences, it is imperative that we identify conditions that are treatable. These efforts may reduce the chances that players will prematurely attribute symptoms to CTE which may lead to hopelessness and thoughts of self-harm," Grashow said.

More than 300 former NFL players have been posthumously diagnosed with CTE.

Before their deaths, many had reportedly developed symptoms of cognitive decline, such as memory loss and mood swings. And some high-profile cases died by suicide — like Dave Duerson, the four-time Pro Bowl safety for the Chicago Bears who shot himself in the chest in 2011 and left a note requesting that his brain be examined for signs of trauma. The following year, another star player shot himself in the chest, the retired San Diego Chargers linebacker Junior Seau; the National Institutes of Health later determined his brain showed damage consistent with CTE.

Junior Seau is honored posthumously on the video board during the NFL Hall of Fame induction ceremony on August 8, 2015, in Canton, Ohio. Seau shot himself in the chest in 2012 and a later analysis of his brain showed he had symptoms of CTE.

Junior Seau is honored posthumously on the video board during the NFL Hall of Fame induction ceremony on August 8, 2015, in Canton, Ohio. Seau shot himself in the chest in 2012 and a later analysis of his brain showed he had symptoms of CTE. / Getty Images

But the precise relationship between CTE and suicidal thoughts is still unclear. Research about suicide shows that a variety of factors can play a role in increasing someone's risk of suicidal thoughts, said Dr. Ross Zafonte, an author on the study and a professor of physical medicine and rehabilitation at Massachusetts General Hospital and Harvard University.

"It may be related to things like isolation, chronic pain, depression, cognitive impairment or even cardiovascular disease — all of which have relationships in former players, all of which could contribute to making any pathology worse, all of which can actually produce problems," Zafonte said, speaking in an interview with NPR.

Because CTE can only be diagnosed with a brain autopsy after death, questions about its prevalence have remained as awareness has grown among football players and the American public alike: Just how common is CTE among former football players? And what portion of current players will develop the disease?

That picture remains unclear.

Aaron Hernandez (81), of the New England Patriots, lost his helmet during this play against the New York Jets in 2011. Hernandez died by suicide in 2017, and researchers found that he had had one of the most severe cases of CTE ever seen in someone his age.

Aaron Hernandez (81), of the New England Patriots, lost his helmet during this play against the New York Jets in 2011. Hernandez died by suicide in 2017, and researchers found that he had had one of the most severe cases of CTE ever seen in someone his age. / Getty Images

Zafonte has treated a wide range of former football players, he said, from younger retirees who "aren't doing so well" to those in their 60s and 70s who are "cognitively intact, by all measures."

"So to assume everyone gets it is a problem," he said. "People are very obsessed, appropriately, with their concerns about CTE. We're not trying to invalidate that in any way. But treating people for the common things that can only make that pathology worse might make your symptoms better."

The Harvard survey, known as the Football Players Health Study, is funded in part by the NFL Players' Association.

Previous studies of CTE have been prone to selection bias, as researchers have largely examined brains donated by families who may have suspected their loved one had experienced cognitive decline. Selection bias could be a factor in the new study, too, the researchers acknowledged, as retirees with more health issues may have been more motivated to respond.

In the new survey, the average age of the respondents was 57.7 years old. For many, in other words, their football careers took place decades ago, in an era when the risks of head injury weren't as well understood, said Dr. Javier Cárdenas, the director of the Concussion and Brain Injury Institute at West Virginia University and neurologist who serves on the NFL's Head, Neck and Spine Committee.

"The yesteryear athlete did not have a concussion protocol, was likely not removed because of a concussion, did not have the time to rest and recover between injuries," said Cárdenas, who was not involved in the JAMA Neurology research. "Yesteryear's athlete more likely was to sustain impact after impact after impact, head injury after head injury after head injury."

In recent years, helmet technology has improved, and the NFL has limited hits in practices, banned helmet-to-helmet tackles and implemented guidelines designed to identify concussions and prevent players with them from returning to a game.

Still, concerns about hits to the head have persisted. Over the past month, at least two youth football players, an eighth grader in West Virginia and a 16-year-old in Alabama, died after hits to the head. And the Miami Dolphins quarterback Tua Tagovailoa left a game after sustaining the third reported concussion of his NFL career, which prompted widespread calls for his retirement.

If you or someone you know may be considering suicide, contact the National Suicide Prevention Lifeline at 988 (En Español: 1-888-628-9454; Deaf and Hard of Hearing: 1-800-799-4889) or by texting 988.