We know concussions can be deadly. Even the NFL has been forced to acknowledge the danger of chronic traumatic encephalopathy to their players. But a new study published in the Canadian Medical Association Journal, shows that even a single, minor concussion could triple a patient’s long-term risk of suicide.

The new study is particularly alarming, as the patients surveyed often sustained just a single concussion in a normal setting, such as a car accident or fall in the house, according to Scientific American, which broke the study’s findings yesterday.

The scientists, led by Donald Redelmeier at the University of Toronto, tracked nearly 250,000 patients, all of whom had sustained at least one concussion, over a 20 year period. Of their sample population, there were over 660 suicides. The average rate of suicide in Canada was about 11 deaths per year, per 100,000 people in 2009. The sample population’s 660 total suicides gave them an average of 31 deaths per year, per 100,000 members of the population, nearly three times the normal level.

The scientists noted that patients who sustained their concussions on weekends, ostensibly during recreational activities like sports, were even further impacted than those who got a concussion during the week. The study, unfortunately, didn’t record the specific circumstances of each patient’s concussion, opting to use days of the week as a marker.

According to the researchers, patients usually took their lives around 6 years after their initial incident, and their risk was further increased by any additional concussions they suffered.

Though the study could not establish any solid reason for the link between concussions and suicide, Redelmeier has a few theories. He told Scientific American that patients who took their own life could have been mentally unstable before they sustained a concussion, even though a smaller group of the study with no pre-existing mental conditions saw similar increases in suicide rates. His other ideas were the possibility that concussions cause inflammation, from which the concussed patient never fully recovers; or that some patients returned to work or other activities before recovering from their injury, leading to stress, frustration, and depression.

Repeated concussions are now known to cause CTE, and other doctors like Lea Alhilali, a physician and researcher at the Barrow Neurological Institute, say it’s no surprise that lesser injuries could still have lasting effects on the brain. Contact sports remain in the spotlight as they struggle for ways to minimize concussions, but the new study points to an even wider population at risk from the damaging consequences of head injuries.