The study, which analyzed 129 accidental bicycle-related deaths in Ontario between 2006 and 2010, found cyclists who didn't wear a helmet were three times more likely to die from brain trauma than those who wore protective head gear while riding.
"Helmets save lives," said Dr. Nav Persaud, a family physician and researcher at St. Michael's Hospital in Toronto, who led the study.
"There are about 70 cycling deaths in Canada every year," Persaud said. "And based on our study, we estimate we could prevent about 20 of them with helmets."
The research, published Monday in the Canadian Medical Association Journal, showed more than three-quarters of the head-injury deaths among cyclists involved a collision with a motor vehicle.
The rest were caused by an impact with another bicycle, a pedestrian or some other object. In more than 10 per cent of cases, death resulted from a fall, data from the Ontario Chief Coroner's office showed. Cyclists killed ranged in age from 10 to 83, and 86 per cent of them were male.
"We found that 88 per cent of people who died were 18 years of age or older, which is important because the helmet legislation in Ontario currently only applies to those younger than 18 years," said Persaud, noting that mandatory helmet use laws vary across the country.
In British Columbia, Nova Scotia, New Brunswick and Prince Edward Island, children and adults of all ages must don a helmet to ride a bike. But in Ontario and Alberta, for instance, only children under 18 are required by law to wear helmets.
Although based on Ontario data, Persaud said the findings have implications for other provinces and territories.
"This study shows that helmets are effective, so anything that promotes helmet use would be effective," said Persaud.
"That would include public awareness campaigns, financial incentives for wearing helmets, such as tax breaks for people who buy helmets, or subsidies for helmets.... In some jurisdictions, they've actually just given away helmets to people, or they've gone to schools and just given away helmets for free."
Still, Persaud agreed helmet use is only one part of the equation when it comes to preventing cyclist deaths. Infrastructure changes, such as incorporating designated bicycle lanes in roadways, can also protect those on two wheels from motorized vehicles.
"Helmets only prevent injuries after a collision takes place," he said. "It would be better to prevent the collision from taking place at all. And infrastructure changes like building separated cycle lanes prevent collisions from taking place.
"That being said, even if we had a perfect cycle infrastructure, cyclists would still interact with cars at intersections, for example, so helmets would still be important."
Alison Macpherson, an associate professor of kinesiology and health science at York University in Toronto, said the study is important because it's the first in Canada, she believes, to examine how cyclists died.
"I think the thing it shows is that helmets do work, and they work to save lives," she said Monday.
However, some cycling advocacy groups are opposed to mandatory all-ages helmet use, arguing that requiring the head gear could deter some people from bicycle-riding and obtaining its health benefits.
Macpherson said research doesn't support that contention.
"I know that those who are against helmet legislation use that as an argument and they say that there will be a negative health impact," she said. "But at least in Canada, that's not what the evidence tells us."
Even so, Macpherson said the focus shouldn't be only helmets, but on making biking safer overall.
Drivers need to be better educated about how to interact with cyclists, including giving them enough space on the road, she said.
Other changes that could make biking less risky include road surfaces that are smooth and without tire-trapping grates that can lead to falls and serious injuries. Trucks could be equipped with barriers that stop cyclists from being pulled under their wheels.
"So if I were going to wave my magic wand and make biking safer, I wouldn't pick helmet legislation as the No. 1 thing to do," said Macpherson. "I think it can be a part of a comprehensive approach to safe cycling that promotes cycling.
"And I think helmets are part of that, absolutely. And this study shows that."
Persaud said he cycles regularly and also encourages his patients to take to their two-wheelers because it's "one great way to build exercise into your schedule."
"So I completely support active transport, which includes cycling and walking to work and school. And I think in the long term, if we make cycling more safe, we'll encourage people to cycle."