The contrast is striking: In provinces that have adopted mandatory helmet legislation for children, bicycle-related head injuries have fallen 45 per cent, compared with a 27-per-cent drop in provinces that have not mandated helmet use.
But more striking still is that, among adults, cycling-related head injuries continue to increase.
In Ontario - which has helmet laws for children but not adults - they have soared 20 per cent over the past three years, according to new research, an incongruity that has led to renewed calls for all-ages legislation.
"We have to do something about bicycle-related head injuries for adults," said Alison Macpherson, an assistant professor in the department of kinesiology and health science at York University in Toronto.
She said that, to date, most legislation has focused on children, for whom cycling is one of the leading causes of traumatic injury. (Only three provinces - British Columbia, Nova Scotia and New Brunswick - have all-ages helmet laws.)
Adults too can benefit greatly from wearing a helmet and legislation seems to be the most effective way of bringing about that change, Dr. Macpherson said.
According to her research, which has not yet been published, 69,670 adults were treated for cycling-related injuries in Ontario emergency rooms between 2003 and 2006. Of that total, 16,172 were head injuries. Over the three years of the study, the number of injuries remained steady, but the number of head injuries increased 20 per cent.
Michael Larkin, a 49-year-old ad sales supervisor at a Toronto newspaper, was one of those statistics.
Last August, he took his son's bicycle out for a quick spin to make sure a mechanical glitch had been fixed. Though he habitually wore a helmet, Mr. Larkin figured it wasn't necessary for a trip around the block.
While he has no memory of the incident, based on eyewitness accounts it appears Mr. Larkin hit a pothole and was propelled off the bike into traffic.
Judging from the extent of his injuries - seven broken ribs, a collapsed lung, broken scapula (shoulder blade), shattered clavicle (collar bone), badly mangled ear and fractured skull - it appears he was hit by at least one car while he lay on the road. Both the frontal and temporal lobes of his brain were damaged, resulting in temporary loss of taste and smell, and some permanent memory loss.
"People kept telling me over and over again how I was lucky to be alive," Mr. Larkin said.
He spent a week in critical care and intensive care, then five weeks in a rehabilitation hospital and several more months as an outpatient.
Mr. Larkin and his doctors say there is no doubt the accident would have left him badly injured even if he had been wearing a helmet, but the skull fracture and brain damage he suffered would likely have been less severe.
"With a helmet, I would still have the fractures, but I wouldn't have spent months in rehab," he said.
Charles Tator, a neurosurgeon who heads the Think First Foundation that promotes brain injury prevention, said the most devastating consequence of a cycling-related accident - be it a banal fall or a collision with a motor vehicle - is invariably brain injury.
"The impact of a head with the pavement, the impact of a head on a car ... you sustain horrible injuries," he said. Aside from the personal pain and suffering, there is a tremendous cost to the health system, he added, noting that it can cost up to $8-million to treat a serious brain injury.
Yet, Dr. Tator said, a helmet costing about $10 can prevent or mitigate most injuries. According to one study, helmets prevent 88 per cent of cycling-related head injuries. That is why he is a staunch advocate of all-ages helmet laws.
"Studies show that with legislation, with rules and enforcement, people do wear helmets. Regulations stop injury and disability, so ... all provinces should enact legislation to force people of all ages to wear bike helmets," Dr. Tator said.
Today, only a minority of adult cyclists voluntarily wear helmets. Barriers to use include a lack of belief in their necessity, and the image that they are uncomfortable and ugly, notably that cyclists have "helmet head" hair.
Dr. Macpherson scoffs at those arguments, saying: "If you're sitting in the ER throwing up because you have a head injury, that's not comfortable either - and your hair doesn't look that good."
Another complaint, based on a highly publicized Australian study, is that when helmet laws are enacted, fewer people cycle. But a B.C. study showed that after the helmet law came into effect, the number of cyclists increased.
In a study published recently in a Cochrane Library review, Dr. Macpherson found that, despite the heated debate on these issues, there is a paucity of good research on the impact of bicycle helmet legislation.
Studies that have been done in North America show that laws clearly increase helmet use, between 45 and 84 per cent. In one Alberta study, the number of children wearing helmets soared after the law was enacted, but there was no effect on adults.
The evidence on prevention of head injuries is also clear in children. A study presented at the Canadian Paediatric Society meeting showed that wearing a helmet cuts the death rate in cycling incidents by 52 per cent.
But the evidence is less clear with adults, largely because the issue has not been well studied.
For Mr. Larkin, however, law or no law, wearing a helmet is a "no-brainer" even for a ride around the block.
"I know that when I'm wearing a helmet, I'm safer. That's what matters."
