At least 25% of former NFL players who died between 2016 and 2021 had CTE, study finds

While professional football and the degenerative brain disease known as CTE have long been linked, true prevalence has remained an open question. A new study finds that, among former NFL players who died between 2016 and 2021, at least a quarter had CTE. Patrick Smith/Getty Images hide caption

For years, as researchers have established a link between repeated impacts to the head and the degenerative brain disease known as CTE , one major question has loomed: Just how common is it — especially among high-risk groups, like professional football players ?

A new study from researchers at Mass General Brigham, published Tuesday in the prominent medical journal The BMJ , seeks to establish a more accurate baseline of CTE prevalence among retired NFL players who have died. Of football players who appeared in at least one NFL game in their careers and who died between 2016 and 2021, the study found that a minimum of around 25% had CTE upon their death.

"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.

Chronic traumatic encephalopathy, or CTE, is a degenerative brain disease that can only be diagnosed with a brain dissection after death . Because of that, most research about the disease has relied on brains donated to researchers by families or by individuals themselves, many of whom had seen or experienced symptoms, such as memory loss or major mood swings, that led them to believe they might have the disease.

That dynamic has long muddied the picture about the actual prevalence of CTE — especially for combat veterans exposed to traumatic brain injuries, or current and former elite-level athletes in contact sports like American football and ice hockey , where blows to the body and head are a regular occurrence.

Daneshvar and his colleagues drew on the large collection of samples at the UNITE Brain Bank at Boston University. The brains of more than 330 NFL players who died between the years of 2008 and 2021 have been donated to the bank. Of those, 93% have been diagnosed with CTE.

Playing football has long been linked to the brain disease known as CTE, but how prevalent it is is still unknown. A new study of former NFL players who died recently found that at least 25% had CTE. Nick Cammett/Getty Images hide caption