A new study is shining light on the origins of homelessness, finding that nearly half of homeless men have suffered a traumatic brain injury and that nearly all of those injuries occurred before the men became homeless.

The St. Michael’s Hospital study found that 45 percent of the homeless men who participated in the research had suffered some form of traumatic brain injury (TBI). And amongst them, 87 percent of their brain injuries had occurred before the men became homeless.

“You could see how it would happen,” said Dr. Jane Topolovec-Vranic, who led the study. “You have a concussion, and you can’t concentrate or focus. Their thinking abilities and personalities change. They can’t manage at work, and they may lose their job, and eventually lose their families. And then it’s a negative spiral.”

The results closely mirrored a similar study released last week, which found that about half of all men entering New York’s jail system aged 16-18 reported suffering a TBI before they were arrested.

"You need to train the correction officers to understand brain injuries so that when somebody may be acting rude or answering back or forgetting what they're supposed to do, it's not a sign of maladaptive misbehavior or disrespect, it's a sign of a brain injury," Wayne Gordon, a brain injury expert at New York's Mount Sinai Hospital, said about that study’s results.

The St. Michael’s study looked at the cases of 111 homeless men and found that assault accounted for some 60 percent of the TBI’s. Drug and alcohol were the leading factors for men under 40, while assault was the most common factor for men over 40 years of age.

However, a significant percentage of the men received their TBI’s in non-violent accidents. Amongst those cases, sports and recreation related injuries accounted for 44 percent of the TBI’s, while motor vehicle accidents or falls made up another 42 percent.

"Injury commonly predated the onset of homelessness, with most participants experiencing their first injury in childhood,” Topolovec-Vranic wrote in the study, which was published in the journal CMAJ Open. “Additional research is needed to understand the complex interactions among homelessness, traumatic brain injury, mental illness and substance use.”

The study participants all hailed from a Toronto homeless shelter. They encompassed a broad age range and all completed a detailed series of questions chronicling their mental health history.

Follow Eric Pfeiffer on Twitter (@ericpfeiffer)