Millions of Canadians will turn their clocks back one hour this weekend, while millions of others will not. This divide is putting Canadians under different time systems — with potentially different consequences for their health.

Most of British Columbia, as well as Alberta, Manitoba and the Northwest Territories are no longer changing their clocks twice a year, joining Yukon and most of Saskatchewan. Most of Ontario, Quebec and the Atlantic provinces will still turn their clocks back on Nov. 1 for the end of daylight saving time.

For Quebec, this could be the last time. Premier Paul St-Pierre Plamondon announced Wednesday that his government is moving to end the twice-yearly clock change, but it has not yet decided which time the province will keep. He said that decision will be made after consulting experts.

Research suggests permanent standard time — the time we return to in the fall — is more closely aligned with the body's internal clock than permanent daylight time, which several provinces have chosen.

Here's what winter time would look like across Canada under proposed time-zone changes Joseph De Koninck, an emeritus professor of psychology at the University of Ottawa, has studied sleep for decades. He said the springtime change is the most problematic because people lose an hour of sleep when they set their clocks forward, creating a mismatch between the body's internal biological clock and solar time.

De Koninck explained that our biological clock uses light to synchronize itself. As daylight changes with the seasons, our circadian rhythms adjust gradually. Making a one-hour adjustment all at once, however, is much more difficult.

"We are able to adapt, but it's not optimal for our health." Why morning light matters Michael Antle, head of the University of Calgary's psychology department and a professor who studies circadian rhythms, said permanent standard time would have been better for Alberta.

Because of the province's northern latitude and position within its time zone, it already has late winter sunrises, Antle said. Permanent daylight time will push them forward another hour. "It's not the choice I would have made," he said of the province's decision.

Antle said daylight time essentially means society has agreed to get up and go to work or school an hour earlier.

Most people's circadian clocks run slightly slow, making them somewhat "night owlish," he said. Morning light helps speed up that clock.

When morning light arrives later, there can be a mismatch between what the body wants to do and what work or school requires.

Antle described this effect as "social jetlag." Antle pointed to population studies that found people exposed to later sunsets slept less and had higher rates of obesity, diabetes and heart disease. He also cited Russian research that found winter depression among young people increased while Russia observed permanent daylight time.

Why some scientists don't support B.C.'s switch to permanent daylight time October 6 Duration Why researchers say permanent daylight time is a bad idea Both researchers distinguish between the disruption caused by changing the clocks and the effects of living on daylight time year-round.

Antle said the spring change creates a sudden shift that can leave people feeling as though they're living on the wrong time for several weeks. Permanent daylight time would extend that mismatch through the darkest months of the year.

He would prefer permanent standard time. Continuing to spring forward and fall back would be a compromise, he said, preserving later summer evenings without the longer-term winter mismatch.

For thousands of workers, lifelong time-zone math will go out the window when B.C. stops changing clocks Time zones in Canada are getting complicated. These maps lay them out Night owls who work regular daytime jobs may struggle the most because they already find it difficult to wake up early, Antle said.

Those darker mornings are also having a real-world impact. Ski hills in Alberta's Bow Valley, for example, are delaying their opening times this winter to give staff more daylight to prepare the slopes before skiers arrive. But most schools and workplaces have less flexibility to change their hours based on when the sun is up.

Changing clocks twice a year a question of public health: prof October 27 Canada becomes a natural experiment Canada's emerging patchwork could give researchers an opportunity to study neighbouring populations living under different time systems.

Antle said he would have preferred a year's notice to collect baseline data before Alberta made the change.

He said researchers should examine mental health, vehicle and pedestrian collisions, school performance and attendance, and workplace attendance and tardiness.

De Koninck noted that researchers now have tools to document sleep habits over time and compare how people adapt in different provinces.

But he expects Western Canadians may make their feelings known before researchers have years of data to analyze. People may not fully understand what permanent daylight time means, he said, until they've experienced a winter with much later sunrises. "Those who've tried it haven't liked it," he said. For De Koninck, the larger concern is what prolonged sleep disruption can mean for people's health.

"If you feel sleep deprived, then you have a host of issues, psychological and physical," he said. "You can't play with your sleep."