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Teenagers who have had a concussion or other traumatic brain injury report higher rates of such harmful behaviours as contemplating suicide, smoking pot and binge drinking, compared with their uninjured peers – and the finding is particularly striking among girls, a study has found.

The research, published online Tuesday in the journal PLOS ONE, investigated 13 harmful health behaviours among almost 9,300 students in Grades 7 to 12, who took part in the 2011 Ontario Student Drug Use and Health Survey developed by the Centre for Addiction and Mental Health (CAMH).

"Both boys and girls were more likely to engage in a variety of harmful behaviours if they reported a history of TBI [traumatic brain injury]," said lead author Dr. Gabriela Ilie, a neuropsychologist at St. Michael's Hospital in Toronto. "But girls engaged in all 13 harmful behaviours we looked for, whereas boys were at higher risk of engaging in only nine.

"Sex matters when it comes to traumatic brain injuries."

For the study, researchers defined the injury as any blow to the head that results in loss of consciousness for at least five minutes or spending at least one night in hospital, although not all concussions/brain traumas cause a person to black out.

One in five Ontario teens surveyed said they had sustained a brain injury in their lifetime, with males reporting slightly more head traumas than females. Team sports were listed as the primary reason behind the injury, followed by falls and bicycle accidents.

Concussions and other brain injuries can cause dizziness, confusion, memory loss, headache, nausea or vomiting. Depending on the severity of the injury, symptoms can persist for some time. Concentration and the ability to remember may be impaired; the person can be irritable, depressed and have marked personality changes; sensitivity to noise and light, along with disturbed sleep, are also common.

They found that girls who had suffered a brain trauma were more likely than boys to report smoking cigarettes, being bullied, contemplating suicide or experiencing greater psychological distress.

Dr. Ilie speculated that the behavioural gap may be due to the underlying differences between girls and boys, including biological factors such as hormones and gender-specific socialization.

"I think what we're looking at is not the result of one factor that we can identify as responsible for the sex difference, as much as a variety of interactive factors, both biological and social," she said.

The study also found that age played a role, with the prevalence of some behaviours becoming more pronounced among those in their late teens, age 17 to 20, compared with the middle adolescence, age 14 to 16.

One study outcome that surprised researchers was a 20-percentage-point increase in alcohol use among TBI-affected girls in their late teens compared with those in their mid-teens, said Dr. Ilie, who called the finding disturbing because regular alcohol consumption is a known risk factor for developing breast cancer.

While both sexes reported experiencing psychological fallout following a brain injury, girls were somewhat more vulnerable to developing such symptoms as depression, anxiety and suicide ideation, the study found.

"Many harmful behaviours in adolescence can be precursors to addiction and mental health issues later in life," said Dr. Robert Mann, a senior scientist at CAMH. "We are seeing important links of adolescent TBI with both substance use and mental health problems and this combination of factors is something to watch, as it may have a serious negative impact on these young people."

However, some symptoms that result from a brain injury don't show up immediately, but may take days, even weeks to manifest themselves.

"You're not quite the same," said Dr. Ilie, noting that a teenager may have difficulty focusing or concentrating in school, be hypersensitive to light and noise and find their mental reactions abnormally slow. "What does it mean now for Mom and Dad? What does it mean for medical practitioners, for school guidance counsellors? It means that we need to stop turning a blind eye to those injuries. Brain injuries are something that we must look at and treat short- and long-term."

She advises parents to have their child assessed immediately by a doctor following a blow to the skull, and to follow up by taking them to a head-injury clinic, where specialists with expertise in treating various consequences of brain trauma will ensure long-term monitoring of symptoms and progress.