A new study in CMAJ Open may shed light on the complex issues around homelessness - almost half of all homeless men in the study had experienced at least one traumatic brain injury, and of these, 87% were injured before becoming homeless.

There is growing interest in the link between traumatic brain injury and homelessness. Although existing evidence suggests a relationship, most studies have been small or poorly designed.

"A myriad of factors may lead an individual to homelessness, and brain injury is just one among many complex issues faced by this population," writes Dr. Jane Topolovec-Vranic, Trauma and Neurosurgery Program, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, with coauthors. "However, the identification of past traumatic brain injury may help to shed light on some of these complex issues."

To better understand the role of traumatic brain injury in homeless men, researchers looked at data on 111 homeless men aged 27 to 81 (mean 54) years who were recruited from a downtown Toronto men's shelter. They found that 45% of these men had experienced a traumatic brain injury; of these, 73% were injured before adulthood, and 87% experienced a first injury before the onset of homeless. Assault was a major cause of injury (66%), followed by sports and recreation (44%) and motor vehicle collisions and falls (42%). In men under age 40, falls from drug or alcohol blackouts were the most common cause of traumatic brain injury, and assault was the most common in men over 40 years old.

Rates of head injury were higher than those among the most at-risk age group in the general population.

"These results suggest that traumatic brain injury may be a risk factor for homelessness," write the authors.

The findings are consistent with previous evidence that shows mental illness is more common in homeless people who have had a traumatic brain injury.

"Screening for [traumatic brain injury] may provide insight into the cognitive, behavioural and mental health issues that homeless persons face. Additional research on temporal relationships and other factors related to traumatic brain injury and homelessness would be valuable," the authors conclude.

The study was conducted by researchers from the Li Ka Shing Knowledge Institute, St. Michael's Hospital; Toronto Rehabilitation Institute, University Health Network; and the University of Toronto, Toronto, Ontario, Canada.