Teenagers who use electronic cigarettes are at risk of graduating to tobacco smoking, a large Canadian study suggests.

The study of more than 44,000 Grade 9 to 12 students in Ontario and Alberta, published Monday in the Canadian Medical Association Journal (CMAJ), shows a "strong and robust" linkage between so-called vaping and subsequent tobacco use.

"We found that youth that had used e-cigarettes were significantly more likely to start smoking a year later," said lead researcher David Hammond, a professor in the school of public health at the University of Waterloo.

"They're more likely to try smoking and they're more likely to become daily smokers."

Correlation or causation?

The big question, said Hammond, is whether it's the use of e-cigarettes that is making some young people smoke.

"A lot of what we're seeing in our study and a lot of other studies out there is a simple fact, and that is the kids who do risky things, the ones that are more likely to try e-cigarettes are also more likely to try smoking," he said from Waterloo, Ont.

David Hammond is a professor in the school of public health at the University of Waterloo. (CBC)

"And guess what? They're also more likely to try alcohol and marijuana. It's all to do with the fact that kids who are susceptible are going to try different things.

"We've had something like two million Canadian youth try e-cigarettes and we'd be foolish if we weren't concerned about kids trying nicotine products at an earlier age than they typically try smoking."

Easier to access

The research, known as the COMPASS study, looked at e-cigarette use among students in 2013/14, with a follow-up a year later. Students were classified into six categories: current daily smokers, current occasional smokers, former smokers, experimental smokers, puffers; and those who had never tried smoking.

Those teens who vaped in the 30 days prior to the start of the study were more likely to start smoking cigarettes and to continue smoking after one year, researchers found.

"Youth may be trying e-cigarettes before smoking because they are easier to access," said Hammond, noting that tobacco cannot be sold to minors.

Rob Cunningham, senior policy analyst for the Canadian Cancer Society, said vaping by young people is of significant concern.

Widely available

Rob Cunningham, Canadian Cancer Society. (Submitted by the Canadian Cancer Society) "Certainly nicotine is addictive and we don't want e-cigarettes to be a mechanism whereby youth get addicted to nicotine," he said.

"And that's why it's so important to prevent kids from using e-cigarettes or starting smoking."

While Canada has not approved nicotine-containing e-cigarettes for sale in conventional retail outlets such as supermarkets, the products are widely available online and in vape stores.

Non-nicotine e-cigarettes, which come in hundreds of flavours, do not require government approval to be sold and make up a large part of the market in Canada.

'The bill should be amended'

However, that is expected to soon change. Bill S-5, which would create new regulations governing e-cigarettes, was approved by the Senate in June and is currently before the House of Commons.

Among its provisions, Bill S-5 would outlaw the sale of vaping products to minors and prohibit the promotion of e-cigarettes containing flavours that appeal to youth, as well as restricting advertising of these products.

But Cunningham said the provisions in Bill S-5 for e-cigarette advertising are weak compared to those for both tobacco and for cannabis, when the latter product becomes legal next year.

"And I think the bill should be amended to strengthen the restrictions on e-cigarettes advertising," he said.

CMA recommends minimum-age ban

The Canadian Medical Association recommends a ban on the sale of all electronic cigarettes to those younger than the minimum age for tobacco consumption in their province or territory.

The doctors group also wants the licensing system tightened to limit the number of outlets where tobacco products, as well as vaping devices, can be purchased, along with restrictions on the promotion of e-cigarettes.

A man exhales vapour from an e-cigarette. The government should continue to work to limit sales to youth, the CMA says. (Frank Franklin II/Associated Press)

"Protecting Canada's youth should be of the utmost importance for government and health-care professionals alike," said CMA president Dr. Laurent Marcoux.

"The findings in this [study] provide even more evidence that the government should continue to work to limit sales and decrease the appeal of products that are often targeted towards Canada's youth," Marcoux said by email.

The CMAJ is editorially independent from the Canadian Medical Association.