Daylight saving time ends Sunday; clocks will fall back one hour at 2 a.m. An extra hour of sleep sounds divine, but a one-hour shift back to standard time this weekend can worsen mental health. The return to standard time is thought less disruptive on human brains and bodies than springing an hour forward in March, when most of Canada enters back into daylight saving time (most of Saskatchewan keeps clocks the same year-round, and Yukon observes Mountain Standard time all year, no “springing forward” or “falling back.”) However, a one-hour shift, in either direction, can impact mental and physical health, experts said. The effects appear more pronounced during the spring transition, with studies showing increased risks of atrial fibrillation (erratic or rapid heart rhythm), heart attacks, stroke, poor immune function, traffic accidents and workplace accidents. The evidence isn’t as robust around the impact of the time switch in the fall, but one study found an 11 per cent increase in depressive episodes. “To say that nothing happens during the fall is not exactly true,” said Dr. Rebecca Robillard, a scientist at the Sleep Research Unit at the University of Ottawa Institute of Mental Health Research at The Royal. The National Post’s Sharon Kirkey spoke with Robillard and Dr. Anya McLaren-Barnett, a pediatric respirologist and sleep medicine specialist at McMaster University.
Why is daylight saving time still a thing?
Daylight saving time was introduced in Canada a century ago, during the First World War, mainly to save energy, “with the idea that if we push back in the spring, people might be able to benefit more from the outdoor light in the evening, thereby cutting the need for artificial lighting, or candles back in the day,” Robillard said.
“Nowadays, in the current context, we know from an energy standpoint there is no major benefit,” especially given the progress in energy-efficient lighting, Robillard said. “There is minimal contribution to the overall energy spending. So, that argument doesn’t stand anymore.”
What is clear, she said, are the health impacts in terms of mental and physical health, “even performance — thinking skills and how people are able to show up at work and perform in their best way.”
How do these time transitions disrupt circadian rhythms?
The regulation of our sleep and emotions is linked to circadian rhythms, or a circadian system, McLaren-Barnett said. Think of it like a master clock in the brain, though components of the circadian rhythm exist in all cells.
“We know that there are mini clocks in a lot of tissues and organs, and all of that machinery is really central to optimize our daily functioning,” Robillard said. “Our digestive tracts, our metabolism, our immune system, our hormones, our temperature — everything is aligned to function optimally during the daytime and to recuperate during the sleep episode.”
There’s a finite number of hours in a day, “so when we shift into daylight savings (when clocks are moved ahead an hour to inject more light into evenings), we’re trying to artificially change our (internal, biological) clock,” McLaren-Barnett said.
“The evidence shows that this is not something that’s as easy as we think it is from a physical and mental health perspective. The misalignment seems not to work well with our bodies and our minds.”
What happens when we “fall back” by one hour?
As the National Post’s Tristin Hopper has succinctly described it, “The cold and darkness of a Canadian winter is depressing in any case. But the effect of daylight saving time is to take a slow darkening process and transform it into a violent, one-day plunge.”
The fall time change has been associated with increased risks of mood disorders, and a worsening of depression and substance use, particularly among men.
A study by Danish and American researchers showed the transition from daylight savings time to standard time was associated with an increase in the number of diagnoses of depression that dissipated over about 10 weeks.
The fact that the association was seen only at the transition from daylight savings to standard time, and not the other way around, suggests that it isn’t due to the one-hour time-shifts (and the resulting disruption of circadian rhythms) “but rather represents a specific consequence of the turning back of clocks in the fall,” the researchers wrote.
One possible explanation is that the sudden advancement of sunset, from 6 p.m. to 5 p.m., “has a negative psychological impact on individuals prone to depression,” and pushes them over the threshold into another bout of depression, the researchers said. People susceptible to seasonal affective disorder in the winter may see the time switch as “an omen of a new depression to come.”
It’s true that as we enter winter months and darker days, it’s hard to untangle the effects of seasonal affective disorder, Robillard said. But it’s also possible that, while we’re already psychologically bracing for that seasonal change, “suddenly — boom — we have this acute event where we shift the clock by one hour.”
Pushing back that sleep-wake cycle by even an hour could be an acute stressor for mental health, she said.
Why is gaining an extra hour of sleep not always ideal?
Because it may be tempting to go to bed later, and it’s not a given that we’ll be able to sleep in later, McLaren-Barnett said. Some people end up sleep deprived “because they indulge in a later bedtime, but then weren’t able to sleep in the next morning, and we have to cope afterwards,” Robillard said.
Some governments are pushing to make daylight saving time permanent. The Ontario government passed legislation in 2020 that would end the twice-annual changing of the clocks, though it hasn’t yet happened. A U.S. senator’s “Sunshine Protection Act” also aims to make DST permanent.
“Some of the arguments are mostly centred around businesses that benefit in having people staying up later, or enjoying an hour extra on the golf course,” Robillard said. But the phrase “sunshine protection” is somewhat misleading. “The big problem is if we were to keep DST this weekend, people in Ottawa would go to school or work in the dark, which is very detrimental,” said Dr. Joseph De Kroninck, a sleep researcher and University of Ottawa professor emeritus of psychology who is in favour of permanently terminating daylight saving time and reinstating permanent standard time. “We need morning light to set our biological clock,” Kroninck said in an email. (Light therapy can boost the moods of people with seasonal affective disorder, and the effects are more pronounced when people are exposed to bright light in the morning.)
We get back into our natural circadian rhythm when we shift in November. But that transition period can still wreak havoc for some, McLaren-Barnett said.
Like anything, not everyone is affected equally, she said. But sleep is intricately linked to mental health, and vice versa. People with an underlying sleep-related disorder like insomnia might be more vulnerable to a one-hour time shifts backwards. The same is true for children who have sleep issues, or neurodivergent children — children with autism or ADHD who rely on structured routines and inputs from the environment, like light, to help regulate their daily schedules.
“If we can do away with having to have that, every year, we should definitely think about moving towards that,” McLaren-Barnett said.
For teens and adults, she recommends avoiding caffeine and other substances that can make it difficult to fall asleep, limiting exposures to screens and not staying up later than normal because it can lead to a worsening sleep debt.