Adults who suffer a concussion are at three times the long-term risk of suicide compared to the general population, according to a new study from Canada.
Unlike some previous research, the new work focused on adults in the general population rather than either athletes or military personnel with head injuries.
"For years there have been examples of serious head injuries leading to potential cases of suicide in military veterans and professional athletes," said senior author Dr. Donald A. Redelmeier of the University of Toronto in Ontario.
"I always worried that even mild concussions acquired in normal community settings might also be a risk, and might cause lasting damage," he told Reuters Health.
The researchers analyzed medical records for adults in Ontario with a diagnosed concussion that was not serious enough to require hospitalization and followed them from 1992 to 2012. More than 230,000 people fell into this category.
Over an average follow-up period of nine years, 667 people who had experienced concussions committed suicide, which is equivalent to a rate of 31 suicides per 100,000 people per year. That's more than three times higher than the suicide rate in the general population, according to the results.
In Canada there are an average of about nine suicides per 100,000 people annually, Redelmeier said.
Weekend concussions appeared to carry an even higher risk of suicide than weekday concussions, the researchers note in CMAJ.
Weekday concussions may happen at work, where there is a treatment protocol, but weekend concussions may be easier to shrug off without really slowing down, Redelmeier said.
Suicide risk after a concussion increased regardless of a patient's past history of psychiatric conditions.
"It's incredibly important to put these things into perspective - the vast majority of people in this study did not die from suicide," Redelmeier said.
"Approximately 4 to 5 million concussions occur annually (in the U.S.)," said Craig J. Bryan of the University of Utah department of psychology in Salt Lake City, who was not part of the new study.
"Also, concussion appears to increase risk for sleep disturbance and depression, and can affect decision-making processes," Bryan told Reuters Health by email. "All of these are risk factors for suicide in their own right."
The study does not prove that concussions cause some suicides, as they may be connected in a different way, Redelmeier said.
People who suffer concussions could be predisposed to suicide beforehand, or a concussion might cause lasting injury to neurons in the brain that never recover, or people who suffer a concussion and don't take enough time to recover may be doing further damage, he said.
"For example, concussions are much more likely to be experienced by individuals who drink alcohol a lot or get into fights," Bryan said. "Alcohol use and aggression are also risk factors for suicide."
"If you've just been diagnosed with a concussion the standard medical advice should be enforced, give yourself plenty of time to sleep," Redelmeier said. "Once you start feeling better, don't try to come back with a vengeance."
"Once you are better, don't forget about it entirely," he said. "If you had a concussion 15 years ago maybe you also want to mention it to your physician."