Concussion damage could linger in an athlete’s brain for at least a year, long after they’ve rejoined their sport, a new study says.

Concussed college athletes had brain changes that remained visible in brain scans up to a year after they’d been cleared to return to play, researchers reported in a study published March 12 in the journal Neurology.

“The presence of significant, long-lasting brain changes after injury reinforces concerns about the consequences of repeated concussions, and to what extent these effects accumulate over time,” lead researcher Nathan Churchill, a postdoctoral fellow in neuroscience research with St. Michael’s Hospital in Toronto, Canada, said in a news release.

For the study, researchers examined 187 college athletes, of whom 25 had suffered a concussion during regular season play in basketball, football, hockey, lacrosse, rugby, soccer and volleyball.

The concussed athletes were also compared to 27 athletes, matched for factors like sex and sport, who hadn’t suffered a concussion.

Athletes had MRI scans taken before their seasons began, as well as five days, one to three months, and a year after returning to play following a concussion.

Concussed players still showed signs of brain injury in MRI scans taken an average five days after concussion, when they’d been cleared to resume play, results show.

Those signs of brain injury lasted for up to one year later, researchers noted.

Compared with pre-injury brain scans, players with concussion had significantly reduced blood flow in their brain’s fronto-insular cortex, a region that helps control thinking, memory, emotion and social behavior, researchers said.

This lower blood flow diminished over time but was still detectable a year after their concussion.

This means the clinical symptoms of concussion used to determine when a player has adequately recovered might not be enough to protect their brain health, an accompanying editorial co-written by Aurore Thibaut and Géraldine Martens, concussion researchers with the University Hospital of Liege in Belgium, said.

“This is crucial because early return to play and incomplete recovery could have serious short-term and long-term consequences, especially in youth,” the editorialists wrote.