Brett Favre's Parkinson's diagnosis reignites questions about football's link to brain disease

Hall of Fame quarterback Brett Favre’s announcement that he has Parkinson’s disease is bringing renewed attention to the potential links between collision sports and a risk of brain disease.

Favre revealed his diagnosis on Tuesday while testifying before Congress about his alleged misuse of taxpayer money. The hearing focused on a welfare scandal in Mississippi, but the subject of Favre’s health arose because he discussed losing an investment in a company that he believed was making a “breakthrough concussion drug.”

“I’m sure you’ll understand why it’s too late for me because I’ve recently been diagnosed with Parkinson’s,” Favre said. 

Favre played 20 seasons in the NFL, mostly for the Green Bay Packers, and retired 13 years ago. In a 2022 interview with “The Bubba Army” radio show, he estimated that he had suffered thousands of concussions. 

“Every time my head hit the turf, there was ringing or stars going, flash bulbs, but I was still able to play,” he said in that interview. “That’s what’s kind of frightening about the concussion thing. It’s the ones that seem minor that do the damage.”

Sports that involve repetitive collisions — such as football, boxing and rugby — carry a risk of concussions and other head injuries. 

“We know that the brain can only take so much, and when there’s this kind of trauma — not even just sports-related, but any kind of repeated trauma to the brain — we know it’s going to affect it down the line,” said Shannon Shaffer, a nurse practitioner at the Cleveland Clinic and liaison at Rune Labs, a neurology-focused software and data analytics company.

Early research has established a likely link between these activities and Parkinson’s, as well as other neurodegenerative diseases like Alzheimer’s, amyotrophic lateral sclerosis (ALS) and chronic traumatic encephalopathy (CTE). Multiple studies have found that a single concussion can raise a person’s risk of being diagnosed with Parkinson’s by more than 55%. 

The NFL did not immediately respond to a request for comment about Favre’s diagnosis and the link between football and neurodegenerative disease. 

Last year, a study found that a history of playing football was associated with 61% higher odds of having Parkinson’s symptoms or being diagnosed with the disease. A 2018 study similarly found that repetitive head impacts from years of playing contact sports were associated with precursors to Parkinson’s. 

Hannah Bruce, an author of the 2023 study, said it can be difficult to determine what role, if any, football played in a case like Favre’s.

“It’s hard to say whether it’s exactly because of the football or if it just increased his risk or odds of developing Parkinson’s disease, or if there’s other factors at play,” said Bruce, who conducted the research at the Boston University Alzheimer’s Disease Research Center. “But we’re seeing more football players come forward. It definitely says something.”

Neurologists who treated boxing legend Muhammad Ali concluded in 2022 that his medical history supported a diagnosis of young-onset Parkinson’s disease, but they could not link the disease to head trauma. Ali died in 2016.

Parkinson’s is a neurodegenerative disease that causes nerve cells in the brain to weaken and die. It can lead to tremors, muscle stiffness, impaired balance and trouble walking and talking. To reduce the symptoms, patients often take prescription medications or receive deep brain stimulation, which sends electrical pulses to nerve cells in the brain.

Repeated trauma to the brain is known to be a potential trigger for the disease, since it can cause inflammation that leads to the death of more nerve cells over time. But it’s one of many risk factors, including older age, an underlying genetic susceptibility and exposure to certain pesticides.

Dr. Kevin Crutchfield, a neurologist at Hackensack Meridian Health, said doctors typically rule out other factors before linking Parkinson’s to football injuries. 

“The default isn’t, ‘Oh, you played football, you got Parkinson’s,’” he said.

Crutchfield added that tens of thousands of men have played in the NFL and, to date, there’s no tidal wave of Parkinson’s diagnoses among them. But the disease isn’t always easy to diagnose, and symptoms do not necessarily develop soon after a head injury.

Thor Stein, director of molecular research at Boston University’s CTE Center and a co-author of the 2023 study, said that in some cases, CTE can be a trigger for Parkinson’s. Many former football players have been found to show signs of the brain disease, which can only be diagnosed post-mortem.

“The more you get these repetitive hits to the head, the longer you are exposed to that, the greater your risk is for developing a number of different degenerative diseases, including both CTE and Parkinson’s disease,” Stein said. “And more recently, surprisingly, we found that in those people who do develop these symptoms that it’s often not the typical pathology, but often it’s CTE that’s causing their Parkinson’s disease symptoms.”

In a July study of brain donors with diagnosed CTE, Stein and his co-authors found that nearly a quarter had exhibited signs of parkinsonism.

Favre said in an interview with TODAY in 2021 that he wasn’t sure whether he had CTE.

Crutchfield said it’s important for players to take breaks after a head trauma to avoid more serious brain injuries. 

“The brain is much more susceptible to recurrent hits if your brain hasn’t had enough time to heal,” he said. “So athletes hiding a concussion because they want to keep playing is not a good thing.”

This article first appeared on NBCNews.com. Read more from NBC News here:

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