Researchers pinpoint when football players are most likely to develop trauma-induced brain disease

Three years ago, Dr. Ann McKee of Boston University published findings that among 111 deceased NFL players, 99% showed signs of chronic traumatic encephalopathy (CTE), brain degeneration that is believed to be caused by repeated head trauma. The research made waves across the football-playing world, from the grade-school level on through the professional leagues, forcing players and their loved ones to confront previously unknown risks associated with the game.

But that study was only the beginning. In the years since it was published, McKee has made further discoveries that give insight not just into the risk of CTE associated with playing football, but how that risk builds over the course of a player’s career. For every 2.6 years of playing football, a player’s risk for developing CTE doubles, McKee and her colleagues found.

“That can be football at any level,” says McKee, who is a professor of neurology and pathology. “[It] doesn’t have to be professional football—can be college, high school football.”

Although there are symptoms associated with CTE, the disease can only be diagnosed after death, which why it is difficult to get a sense of how players are being affected over time. The study highlighting McKee’s new work was published earlier this month in Annals of Neurology. 

Critics of the 2017 study complained that researchers only tested brains that were donated under the assumption that CTE was likely. This more recent study attempts to correct for that with additional controls. Researchers at Boston University took a sample of 266 deceased football players from brain banks at the Veterans Affairs–Boston University–Concussion Legacy Foundation (VA-BU-CLF) and the Framingham Heart Study. McKee and her colleagues made sure to acquire brains of players that had been involved in contact and collision sports across levels, from youth to professional. The results are notable: “Each additional year of play corresponded to 30% higher odds of having CTE at death.”

The work also highlights important inflection points. Players who played 4.5 years or less are 10 times less likely to have CTE than those who play longer. At 14.5 years of playing football, players are 10 times more likely to develop CTE than those who play fewer years. “It’s a good argument for starting to play later,” says McKee. “You won’t have the cumulative risk of playing since you were five.”

Researchers are now working on the holy grail of CTE study: being able to detect it in living humans. Once it can be identified without doing a post-mortem tissue analysis, researchers will be able to monitor the disease and develop a treatment. Recent research shows that scientists may be able to use PET scans to discern a certain pattern of a protein called tau that has been associated with CTE. However, it is still early.

Dr. Bennet Omalu, at the Brain Injury Research Institute, was the first to recognize CTE in the brains of deceased athletes in 2002. At the time, the National Football League had the Mild Traumatic Brain Injury Committee, which has since been renamed the Head, Neck, and Spine Committee. It has repeatedly put out research that refutes a connection between playing football and brain injury or disease. Five years after Omalu’s finding, the NFL changed its guidance for players on playing post-concussion. In 2016, the NFL announced it would put $100 million into medical and neuroscience research toward understanding CTE and head injury. It has also put money into better helmets, though helmets may do little to prevent concussion.

Other forms of prevention may prove a more fruitful course of action. In her work, McKee has found that there is a particular genotype that is associated with certain outcomes of CTE. “Inflammation is key, is critical to the development of CTE, and people’s genetic predispositions toward different types of inflammation may determine whether or not you’re more or less susceptible to the disease,” she says. “What’s going to come up more and more is genetic variables that determine susceptibility.”