Repetitive head impacts can cause cell loss, inflammation, and vascular damage—even without CTE
Lacing up cleats, dusting down pads, pumping up soccer balls: for many young athletes and weekend warriors, fall is the time to get back on the sports field. And while most accept the outside risk of a twisted ankle, strained hamstring, or even a torn ACL for the benefits of exercise, team play, and enjoyment, new Boston University research suggests they might also be putting their brain health on the line.
In a study of young former athletes—all under the age of 51, some just in their 20s—BU researchers found that repetitive head impacts from contact sports like football and soccer can cause a slew of negative brain changes, including neuron loss, inflammation, and vascular damage. The changes were visible even among those who didn’t have chronic traumatic encephalopathy, or CTE, a neurodegenerative disease that’s become synonymous with football and other collision-heavy sports. The research was conducted at the BU CTE Center, a world leader in studying the effects of head trauma from sports and military service.
“These results have the potential to significantly change how we view contact sports. They suggest that exposure to repetitive head impacts can kill brain cells and cause long-term brain damage, independent of CTE,” says Jonathan Cherry, a BU Chobanian & Avedisian School of Medicine assistant professor of pathology and laboratory medicine. The results were just published in Nature. “These findings suggest that repetitive head impacts cause brain injury much earlier than we previously thought. [They] highlight that even athletes without CTE can have substantial brain injury.”
According to Cherry, the changes could disrupt communication in the brain, leading to potential memory issues, and increase an individual’s risk of neurodegenerative disorders like Alzheimer’s disease.
Lasting Consequences of Repeated Hits to the Head
For the study, Cherry and his colleagues focused their attention on the frontal cortex, the part of the brain that handles a range of important executive functions, like solving problems, remembering events, interacting with others, and expressing emotion; it also contains the regions subject to the highest forces during an impact. They began by examining frozen human brain tissue from 28 men whose brains had been donated to the CTE Center after their deaths, dividing them into three groups: a control group who hadn’t played contact sports, a group of athletes with a CTE diagnosis, and a group who’d been exposed to repetitive head impacts in sports, but had not been diagnosed with CTE.
In addition to looking at the samples under the microscope, the researchers performed single-nucleus RNA sequencing, a powerful technique that gives a genetic readout of millions of brain cells. The BU team then compared what they’d seen with the microscope to more than 100 other cases from the BU-led UNITE Brain Bank—a repository of more than 1,500 donated brains—as well as other published datasets.
Cherry says they expected to see some brain changes among those who’d played contact sports, but they were surprised by the intensity of damage, particularly given the focus on younger individuals. Both sets of athletes—those with and without CTE—had similar levels of inflammatory and vascular changes. Strikingly, the contact sports players had an average of 56 percent fewer cortical neurons than those in the nonplaying control group. The majority of the athletes had played American football.
“Repetitive head injury can lead to many types of brain diseases—CTE is just one of them,” says Cherry, who’s also director of the digital pathology core at the BU CTE Center. “These changes were significant, they happened early, and they predispose people to a number of different things,” including Alzheimer’s and Parkinson’s diseases.
Although the researchers had limited clinical information on the subjects—and not all had any significant behavioral symptoms at the time of their death—Cherry says the lost neurons would have been “really important for communication and signaling, some cognitive and executive function,” making it harder to relay signals from one brain area to another. That could lead to issues like poorer memory and increased impulsivity.
“We’re finding that repeated hits to the head, whether or not they cause a concussion, have lasting consequences,” says Morgane Butler (CAMED’25), who recently completed her PhD at BU and is the paper’s lead author. “The findings in this paper show that these changes can start after head trauma exposure in the absence of a CTE diagnosis and persist after people stop playing sports.”
Informed Decisions to Play
The researchers hope their work can pave the way for future studies on understanding the brain changes that come from repeated head impacts and on detecting them during life. At the moment, many brain conditions—including CTE—can only be definitively diagnosed after death. “The study also identified many genes that were elevated in response to head trauma that can be investigated for future biomarker discovery,” says Butler, who’s now a postdoctoral researcher at pharmaceutical company Eli Lilly. Biomarkers are molecules that give clues to the body’s health and can potentially be tracked using blood tests.
Another goal of the research team: preventing damage in the first place. Cherry, a former athlete himself—wrestling and jiu-jitsu—says his goal isn’t to end contact sports, but to make them safer, raising awareness of their potential long-term risks and finding ways to mitigate them. “I get the appeal of sports and it’s good to be active. That’s why part of the message is not trying to cancel anything, but getting the information out there, so people can understand what’s happening to them.”
This story was originally published by Boston University on September 17, 2025.