Men who are heavy drinkers and homeless for long periods of time have 400 times the number of head injuries as the general population, according to a new study by researchers who said they were shocked by their findings.

These men have 170 times as many severe head injuries as the general population and 300 times as many injuries that cause bleeding in the brain.

The study by Dr. Tomislav Svoboda, a family physician at St. Michael’s Hospital, appears online in Emergency Medicine Journal.

The study also looked at head injuries in the general homeless population and among people who are vulnerably housed, meaning they live in crowded, unsafe or unaffordable housing or are in danger of becoming homeless. Both these groups had about 23 times the number of head injuries as the general population, but rates much lower than the chronically homeless.

Previous studies of head injuries among people who are homeless have been based on interviews. Dr. Svoboda, a researcher in the hospital’s Centre for Research on Inner City Health, said his study is the first based on actual Emergency Department records over five years and the first to compare people who are homeless with the general population based on that data. They looked at all head injuries from slight concussions to brain hemorrhages.

“We were shocked by the number if head injuries,” said Dr. Tomislav. “In medicine, we worry when something occurs two or three times more often in a particular patient group, but to talk about magnitudes of 300 or 400 is unheard of.”

Dr. Svoboda also found the length of time between head injuries shortened as the number went up. The mean interval between head injuries was 231 days. That decreased by an average of 11.8 days with each subsequent head injury.

Having a seizure disorder, drug dependence or a head injury in the previous year were the main predictors of whether someone would have another head injury. Previous research has found that people who are homeless are at greater risk of being assaulted or being victims of violence. Dr. Svoboda said the numbers in his study suggest that head injuries are causing physical changes such as dizziness, memory loss, impaired cognitive functions and mental health issues, which lead to more head injuries.

“We need to do something for this group--we’re seeing data that suggests they are in a downward spiral,” said Dr. Svoboda. “We need to develop programs to understand and treat this serious and permanent problem. When the brain is injured, you can’t fix it. We need to identify and support these people.”

Dr. Svoboda said one answer could be to do more CT scans on people identified as being at risk.

In the general population in Canada, about 12 in every 10,000 men have a head injury that might involve a brain injury each year. Among the chronically homeless the number is 4,800 every year. Among men who are in low income housing each year, 370 in every 10,000 have such a head injury.

This study was funded by the Central East Health Information Partnership, the former City of Toronto Shelter, Housing and Support Division, Physician Services Inc. and the Canadian Institutes for Health Research.