Year-round daylight time has a dark side. Here’s how Canada can prepare for it

This Nov. 1, as a large swath of Canada does away with seasonal time change and shifts to year-round daylight time instead, experts are warning about the health consequences of this move, which will bring darker mornings through the winter.

For people in British Columbia, Alberta, Manitoba, Northwest Territories and parts of Northwestern Ontario, the shift means no more adjusting every spring and fall – plus one more hour of light in the evenings.

In government polls on time change, those in favour of permanent daylight time voiced their desire for an extra hour of light after work to see friends and family, exercise and shop.

But for all the perks, the move comes at a cost. Through winter, without setting the clocks back, more of the mornings will be shrouded in darkness, forcing workers and students to commute well before sunrise.

Scientists caution that darker mornings do a number on our sleep, hitting adolescents, early shift workers and those with sleep disorders the hardest. Shortened hours of rest have been linked to numerous health harms, from depression and cardiovascular risk, to workplace injuries.

Researchers have even discovered dips in productivity, school attendance and grades at the edges of time zones where sunrise comes latest.

With so many concerns, why is half of Canada embarking on its own experiment with permanent daylight time? That’s the question from authors of a strongly worded paper published ahead of the Nov. 1 changes in the Canadian Medical Association Journal.

“Ending biannual clock adjustments may eliminate transition harms that last a few weeks,” wrote the authors, “but the health effects of permanent [daylight] time are likely to be chronic.”

The authors are pushing for countermeasures – better pedestrian infrastructure to make travel safer through darker mornings, later start times for students, as well as public health messaging on nighttime sleep habits.

The Globe spoke, separately, with two of the paper’s co-authors, Patrick Baylis, an associate professor at the University of British Columbia’s Vancouver School of Economics, and Ralph Mistlberger, professor of psychology at Simon Fraser University.

What’s behind the broad appeal of permanent daylight time, for people and for governments?

Mistlberger: The sun rises very early in the summer, and many of us are sleeping through a good deal of that. With daylight time, we are essentially “saving” some of that missed sunshine by tacking it on to the end of the day.

When people are polled on time change, it’s always, “We don’t like switching, but we love those summer evenings. Why not have more of those?” Those warm evenings with the sun setting at 10 p.m., they fill us with this good feeling. Why wouldn’t you vote for that, without any other information?

And that’s been the problem – it’s a knowledge translation problem.

More than the long summer evenings, what people will end up noticing is that in winter, the sun might not even rise until 9 a.m. when they’re at work already. Meaning they will have not seen any daylight in the morning.

What has struck me here is that more health experts were not consulted on this. It’s hard to penetrate the powers of populism. Governments want what the people want, but people don’t always know what’s good for them.

Everywhere this has been tried and abandoned, it’s because ultimately, people didn’t like it. They liked the idea of summer evenings but they don’t like the reality of dark winters.

What are the documented health harms of later sunrises, all year long?

Mistlberger: It all comes down to morning light and our internal biological clocks. The effect of later sunrise is that it’ll be more difficult to wake up early in the dark, and more difficult to go to bed early and fall asleep.

At the same time, our social clock will not change: we’ll still have to get up at the same time for our regular work and school schedules. The mismatch between the social clock and our biological clock is called “social jet lag.” With year-round daylight savings time, there will be an extended period where social jet lag is increased in the winters.

When there is misalignment and short sleep, you get a whole spectrum of negative health outcomes. What we know from copious epidemiological evidence is that people who sleep only five or six hours are at greater risk of developing diabetes, metabolic disorders, cancer and cardiovascular disorders.

Certain populations, you write, will find these darker mornings especially challenging. Let’s start with adolescents, who have later circadian rhythms.

Mistlberger: Teenagers are also the least able to avoid social media and the phone in front of their face in bed at night. It’s a source of light, sound and busyness.

All of that is stimulating the nervous system, allowing you to stay up later than you should. The artificial screen light also suppresses melatonin, the biological signal for, “It’s biological nighttime. Go to bed.”

So now you’ve got artificial light in the evening but also less natural light in the morning. The two will conspire to make people more socially jetlagged.

Which other populations might this unduly affect?

Baylis: Early morning shift workers. People with longer commutes, since they need to start earlier. In general, people with less flexible schedules that require them to get up early are most likely to be affected. Other vulnerable populations, besides students, would be those who are naturally inclined toward staying up later – people who already struggle to sleep an adequate amount.

From a transportation safety perspective, we should also be thinking about individuals commuting in rural or lower-income communities with more limited lighting, particularly in areas with fewer sidewalks.

What are the knock-on effects for learning and productivity?

Baylis: It’s all related. This affects sleep and then sleep affects health. Then, sleep and health affect schooling outcomes, which then shape economic outcomes.

We can learn a lot about how later sunrises affect people by studying those who live at opposite ends of one time zone. What have you found?

Mistlberger: Studies have looked at whether there’s a difference in people’s health, academic outcomes, earnings and productivity from one edge of the time zone to the other. This really blew me away – it’s shocking. One study in Florida discovered that being on the edge of the time zone where sunrise is earlier was equivalent to changing class size from 40 students to 20 students. When you have fewer students per teacher, you get better academic outcomes, and that was the effect of this time zone position.

Baylis: The economic evidence was surprising to me. This pattern shows up where you see less productivity and lower wages on the western edge of the time zone, where sunrise comes later. You can imagine workers being less effective at work because they’re sleepier. If everybody in an area is experiencing sleep loss and getting less done during the day, it can have compounding effects. Whereas if you’re in a city where people are well rested, you can see how it would lead to higher overall levels of productivity, with more productive firms looking to locate there. They’re all tiny things that stack on each other.

You’re urging countermeasures to darker mornings, including safer roads.

Baylis: Nothing new needs to be invented here. But particular attention needs to be paid to deploy existing safety technologies on routes likely to see much more early morning foot traffic. It might be installing new lights in school zones.

You also propose later or more flexible start times for students and certain workers.

Baylis: We know that adolescents really suffer under late sunrises. California’s state-level intervention shifted public middle and high school start times later. Shifting start-times to be more aligned with the sun has beneficial effects on student performance.

Mistlberger: At work, organizations will have more control over this but they won’t do it unless they’re informed about the value of it to their workers’ productivity and safety.

On the flipside, Japan and South Korea have observed permanent standard time for decades. Has the option been popular there?

Baylis: It’s been in place there for a long time and people don’t seem to find it objectionable. It’s not doing annoying things to schedules in the spring and fall, and it’s not putting people through the early morning challenges we’re concerned about.

Will Canada’s experiment with year-round daylight time last?

Mistlberger: Yukon has actually been on permanent daylight time since 2020. Governments say, “It doesn’t seem to have affected them.” But the sun rises so late there, it’s late no matter what time system you choose. It’s not informative.

It would not surprise me if we abandon this after a short period of time. I wish we weren’t doing it but I’m very curious. There’s a little scientist inside of me thinking, this is going to be interesting.

The interviews have been compiled, edited and condensed for clarity.

The science of time change sheds light on the subject

While it’s clear that few enjoy resetting their clocks twice a year, the issue of daylight versus standard time is more divisive.

But research points to the health advantages of permanent standard time with its earlier sunrises. At the same time, several global test cases illustrate the unintended consequences of doing daylight time year-round.

Internationally, three large-scale experiments with permanent daylight time proved unpopular.

During the oil crisis in 1974, the United States implemented permanent daylight time to save energy. Within a year, officials backpedaled, following outcry over pedestrian accidents, children trundling to school in pitch black conditions. (That hasn’t deterred American lawmakers from floating new legislation to give permanent DST another try.)

Chile ventured the concept in 2015 but backtracked a year later, after protests from fruit growers, who found dark mornings delayed their work day, productivity plummeting by 15 per cent.

In 2014, Russia abandoned its own three-year trial after traffic accidents spiked and people in the northern reaches complained of brutally gloomy mornings.

Along with experts studying sleep and circadian rhythms, the authors of a recent paper in the Canadian Medical Association Journal argue that permanent standard time would have been the wiser option, since it preserves more morning light and better coordinates our work and school schedules with our bodies, which naturally want to follow the sun.

A 2025 Stanford modeling study looked at circadian rhythms, noting how aligned or misaligned they become through seasonal time changes, permanent daylight time and permanent standard time. Then, they related the information to cardiovascular risks and a range of health issues. Biannual switching proved the most harmful, followed by permanent daylight time, with standard time holding the most health benefits. The researchers concluded that standard time was the recommended system.

Despite this, government polling on time changes often omits permanent standard time as an option, frustrating experts. Public surveys tend to offer just two choices: permanent daylight time, or changing the clocks twice annually – a deeply unpopular option.

The authors of the CMAJ paper are urging provincial governments making the shift this November to watch for the health consequences of later sunrises, to help inform policy choices going forward.

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