As the Panthers and Broncos faced off in the third quarter of last night’s Super Bowl, wide receiver Philly Brown suffered a possible concussion—and to the disappointment of Panthers fans, he never returned to the game. But for good reason: concussions are now known to be much more serious injuries than once thought. And the danger may not be limited to the immediate repercussions. Researchers have already linked more severe traumatic brain injury to later suicide—particularly in military veterans and professional athletes—and have more recently explored the connection between concussion and depression.

Now, new research published in the Canadian Medical Association Journal shows that even mild concussions sustained in ordinary community settings might be more detrimental than anyone anticipated; the long-term risk of suicide increases threefold in adults if they have experienced even one concussion. That risk increases by a third if the concussion is sustained on a weekend instead of a weekday—suggesting recreational concussions are riskier long-term than those sustained on the job. “The typical patient I see is a middle-aged adult, not an elite athlete,” says Donald Redelmeier, a senior scientist at the University of Toronto and one of the study’s lead authors. “And the usual circumstances for acquiring a concussion are not while playing football; it is when driving in traffic and getting into a crash, when missing a step and falling down a staircase, when getting overly ambitious about home repairs—the everyday activities of life.”

Redelmeier and his team wanted to examine the risks of the concussions acquired under those circumstances. They identified nearly a quarter of a million adults in Ontario who were diagnosed with a mild concussion over a timespan of 20 years—severe cases that resulted in hospital admission were excluded from the study—and tracked them for subsequent mortality due to suicide. It turned out that more than 660 suicides occurred among these patients, equivalent to 31 deaths per 100,000 patients annually—three times the population norm. On average, suicide occurred almost six years after the concussion. This risk was found to be independent of demographics or previous psychiatric conditions, and it increased with additional concussions.

For weekend concussions, the later suicide risk increased to four times the norm. Redelmeier and his fellow researchers had wondered whether the risk would differ between occupational and recreational concussions. They did not have information about how the concussions happened, so they used day of the week as a proxy. Although they do not know why weekend risk is indeed higher, they suspect it may be because on weekends medical staff may not be as available or accessible or people may not seek immediate care.

Although the underlying causes of the connection between concussion and suicide are not yet known, Redelmeier says that there were at least three potential explanations. A concussion may be a marker but not necessarily a mechanism of subsequent troubles—or, in other words, people who sustain concussions may already have baseline life imbalances that increase their risks for depression and suicide. “But we also looked at the subgroup of patients who had no past psychiatric history, no past problems, and we still found a significant increase in risk. So I don’t think that’s the entire story,” he notes. One of the more likely explanations, he says, is that concussion causes brain injury such as inflammation (as has been found in some studies) from which the patient may never fully recover. Indeed, a study conducted in 2014 found that sustaining a head injury leads to a greater risk of mental illness later in life. The other possibility is that some patients may not give themselves enough time to get better before returning to an ordinary schedule, leading to strain, frustration and disappointment—which, in turn, may result in depression and ultimately even suicide.

Lea Alhilali, a physician and researcher at the Barrow Neurological Institute who did not participate in this study, uses diffusion tensor imaging (an MRI technique) to measure the integrity of white matter in the brain. Her team has found similarities between white matter degeneration patterns in patients with concussion-related depression and noninjured patients with major depressive disorder—particularly in the nucleus accumbens, or the “reward center” of the brain. “It can be difficult to tease out what’s related to an injury and what’s related to the circumstances surrounding the trauma,” Alhilali says. “There could be PTSD, loss of job, orthopedic injuries that can all influence depression. But I do believe there’s probably an organic brain injury.”

Alhilali points to recent studies on chronic traumatic encephalopathy (CTE), a progressive degenerative brain disease associated with repeated head traumas. Often linked to dementia, depression, loss of impulse control and suicide, CTE was recently diagnosed in 87 of 91 deceased NFL players. Why, then, she says, should we not suspect that concussion causes other brain damage as well?

This new study may only represent the tip of the iceberg. “We’re only looking at the most extreme outcomes, at taking your own life,” Redelmeier says. “But for every person who dies from suicide, there are many others who attempt suicide, and hundreds more who think about it and thousands more who suffer from depression.”

More research needs to be done; this study was unable to take into account the exact circumstances under which the concussions were sustained. Redelmeier’s research examined only the records of adults who sought medical attention, it did not include more severe head injuries that required hospitalization or extensive emergency care. To that extent, his findings may have underestimated the magnitude of the absolute risks at hand.

Yet many people are not aware of these risks.

Redelmeier is adamant that people should take concussions seriously. “We need to do more research about prevention and recovery,” he says. “But let me at least articulate three things to do: One, give yourself permission to get some rest. Two, when you start to feel better, don’t try to come back with a vengeance. And three, even after you’re feeling better, after you’ve rested properly, don’t forget about it entirely. If you had an allergic reaction to penicillin 15 years ago, you’d want to mention that to your doctor and have it as a permanent part of your medical record. So, too, if you’ve had a concussion 15 years ago.”

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