Concussion due to everyday and recreational activities triples long-term suicide risk. The risk increases even further if these injuries occur during the weekend, results of a large study show.

"The increased risk applied regardless of demographic characteristics, was independent of past psychiatric conditions, became accentuated with time, followed a dose-response gradient and was not as high as the risk associated with past suicide attempts," the investigators, led by Donald Redelmeier, MD, senior core scientist at the Institute for Clinical Evaluative Sciences and a physician at Sunnybrook Health Sciences Centre, Toronto, Canada, write.

The researchers, who studied the records of more than 230,000 patients with concussion covering a 20-year period, add that "regardless of interpretation, these findings suggest that an association between concussion and suicide is not confined to the military."

The study was published online February 8 in the Canadian Medical Association Journal.

Overlooked, Trivialized Issue

Dr Redelmeier told Medscape Medical News that he undertook the research because concussion in the general population has often been overlooked.

"There have been some case reports suggesting that severe head injuries might lead to suicide in professional athletes as well as military veterans, but I've always wondered about whether even a mild concussion acquired in normal community settings might also be a risk factor for suicide in the patients I look after."

Moreover, concussion is commonly trivialized in the media, Dr Redelmeier noted.

"Concussions are often blown off in popular media, where some heroic adventurer gets a blow to the head, is knocked out, and then shrugs it off with macho bravado," he said.

For the study, the team performed a longitudinal cohort analysis of adults on the Ontario Health Insurance Plan database who met the International Classification of Diseases, 9th Revision, diagnostic criteria for concussion from 1992 to 2012. Severe cases that resulted in hospital admission were excluded.

During the study period, 235,110 patients were diagnosed with concussion, of whom 52% were male. The mean age was 41 years, and 86% lived in an urban location. The majority of concussions (n = 195,170) occurred on a weekday.

Over a median follow-up period of 9.3 years, there were 667 deaths by suicide; the mean time from concussion to suicide was 5.7 years. This was equivalent to 31 deaths per 100,000 patients annually.

Weekday concussion accounted for 519 suicides, at an absolute suicide risk of 29 per 100,000 patients annually. This is three times the population norm. Weekend concussion accounted for 148 suicides, at an absolute risk of 39 per 100,000 annually, which is four times the population norm.

The difference in suicide risk between weekday and weekend concussion equated to an increase by one third, at a relative risk of 1.36 when all potential confounding factors had been taken into account.

As expected, suicide risk was associated with male sex, low socioeconomic status, and poor psychiatric diagnosis. The largest association was seen with prior suicide attempt, followed by substance abuse, at relative risks on multivariate analysis of 5.65 and 3.60, respectively.

Additional concussions were also a risk factor for suicide, with each extra concussion increasing the risk by 30%. The association between concussion and suicide increased over time.

Weekend Concussion

Regarding the reasons for the increased rate of suicide among people who had concussions on weekends, Dr Redelmeier said that there are several possibilities.

"One explanation is that they just don't go for treatment at all, unlike the safeguards that occur relative to workplace injury. If you are knocked out, your employer is going to want you to get checked out, as will your work colleagues, and those safeguards are just not apparent on Saturdays and Sundays on your own recreation.

"If you are motorcycling, for example, and you go down, there's nobody that you're accountable to or is accountable to you, so it may be that there's a decreased willingness to seek care, or less safeguards," he said.

"There are other alternative explanations, including this notion of how you feel about it after the fact. If it was a truly self-selected activity where you've got nobody to blame but yourself, you might not get the same degree of support from your families or friends compared to a misadventure in the workplace. But that's open for debate, and more research is needed for those alternate interpretations," Dr Redelmeier added.

Another important finding was that a substantial proportion of the individuals who committed suicide had seen a doctor in the last weeks and months of life. Specifically, 51% of weekend and weekday concussion patients who committed suicide had seen a physician in the week before their death; 77% and 71%, respectively, had done so in the month before their death.

Dr Redelmeier emphasized: "That was a major missed opportunity for prevention. Nobody has to die from suicide. A physician might not be able to normalize the situation and bring the patient back to perfection, but a physician is certainly able to stop a bad situation from getting much worse. That was our single most important lesson."

For Dr Redelmeier, the strongest recommendation that emerges from the study concerns the prevention of concussion, specifically in terms of wearing protective gear.

"When going skiing, please wear a helmet, get yourself trained, stay sober, don't be reckless and foolish, and follow the rules. And that applies whatever you're doing as a part of your normal activities, especially your weekend activities," he said.

"Look after your head. Just because it's surrounded by bone does not mean it's invulnerable; it does not mean you are as robust as Indiana Jones," he added.

When concussions do occur, Dr Redelmeier advises that patients rest, that they take their time when they start to feel better, and that they not forget about their concussion.

"If you had an episode of an allergic reaction to penicillin 15 years ago, you would want to tell your doctor about that, and you would want that as a part of your medical records," he said. "Similarly, if you've had a concussion 15 years ago, you would want to tell your doctor about that, you would want it to be a part of your medical records."

Even Mild Injury a Suicide Risk

Commenting on the study for Medscape Medical News, Thomas W. McAllister, MD, chair of the Department of Psychiatry, Indiana University School of Medicine, in Indianapolis, said one of its strengths is the large number of patients and the fact that the majority of the cohort had government-funded health insurance.

"One of the confounders that sometimes creeps in these studies is that you are really just accessing people who access the healthcare system. Of course, if you don't have payment for it, that's one of the reasons people won't come forward and therefore won't be diagnosed, and so you miss a whole segment," he said.

Discussing the apparent novelty of the findings, Dr McAllister noted that the focus on sport-related concussion and military-related blast concussion over the past 5 to 10 years has meant that "people have often lost sight of the fact that concussion is synonymous, in most respects, with mild traumatic brain injury."

Explaining the link between concussion and suicide, Dr McAllister said: "Exposure to a brain injury of pretty much any severity, whether mild, moderate, or severe, carries with it an increased risk of developing psychiatric illness."

He continued: "You can see different studies purporting to show different exact risk increases, but the bottom line is that there's severalfold increase in the relative risk of depression and anxiety disorder, and there's a much more modest increase, probably, in the rate of people with psychosis or schizophrenia."

Depression, he noted, is the leading cause of suicide, "so one way of connecting these dots is that brain injury increases the risk of depression, depression increases the risk of suicide, and that may be accounting for some of the association."

Interestingly, psychiatric illness is a predisposing factor for brain injury. "So there's this fascinating interaction between psychiatric illness and brain injury, which I think we're only beginning to unravel at this point," he said.

Dr McAllister was not surprised by the finding that the majority of individuals who committed suicide had recently visited a physician. He noted that if one studies the literature concerning suicide, it is "remarkable" how many consistently show the same thing.

"If you're coming to see a physician for some kind of physical complaint, and the physician has 20 minutes or something like this to diagnose it, and if the patient doesn't call to their attention the fact that they're feeling depressed or their life is not worth living, then it's not likely to come up in the course of the exam," he said.

Dr McAllister continued: "Which isn't to say that we as a profession shouldn't do better. I think we should, and in fact, people are moving towards a much more aggressive kind of assessment and screening for suicide.

"We know what a lot of the risk factors are, but even when people meet a lot of those risk factors, sometimes folks will deny it, or a certain percentage of folks who kill themselves do it on an impulse."

Dr McAllister noted that the best predictors of suicide are previous attempts, male sex, access to lethal means, older age, and substance abuse.

"So we know a lot of the predictors, and those are born out in this study as well, but there's still a whole lot of people who meet those criteria who don't kill themselves," he said.

"It's really a matter of, okay, we can identify a group who are at higher risk, but that's still thousands of people, so how do we find the needles in the haystack, if you will?"

In conclusion, Dr McAllister said: "I think that the nice thing about this paper is that it does identify a history of mild brain injury as a significant risk factor among others for suicide.

"For example, if you're doing an assessment and somebody is male, has guns at home, is abusing substances, and is feeling despondent, and they also tell you that they've had a brain injury, they're probably at higher risk than somebody who had all those factors but didn't have a brain injury.

"It's another important identifier for people at risk to kill themselves."

This research was supported by a Canada Research Chair in Medical Decision Sciences, the Major Frederick Banting Chair in Military Trauma Research, the Canadian Institutes of Health Research, the Canadian Forces Surgeon General's Health Research Program, and the BrightFocus Foundation. The authors have disclosed no relevant financial relationships.

CMAJ. Published online February 8, 2016. Abstract