On November 1, Manitoba will adopt permanent daylight saving time (pDST), joining British Columbia, Alberta, Saskatchewan, Yukon, and the Northwest Territories. The decision, which was announced in mid-September, followed a survey of 72,000 Manitobans, 92% of whom said they wanted to abolish seasonal time changes once and for all.

Policymakers and clinicians should consider how moving the clock back or ahead will affect Canadians’ health not only during the transition but also in the long term, experts said.

Current evidence favors permanent standard time (pST) for sleep, mood, and general health because it better aligns with the body’s circadian clock, Raymond W. Lam, MD, associate head of graduate and undergraduate medical education at University of British Columbia’s Department of Psychiatry in Vancouver, told Medscape News Canada. Lam is the lead author of a newly published analysis exploring the public health implications of clock changes.

“Conversely, pDST will have negative impacts on various factors, especially in the winter,” he explained. “We expect more problems with insomnia, difficulty waking up in the morning, sleepiness on the morning commute to school and work, and increased depression in the winter. Clinicians should prepare to see health consequences related to these effects.”

Morning Light Essential

Human circadian rhythms run slightly slower than the solar day (ie, the time it takes Earth to rotate once on its axis: 24 hours). The master circadian clock — the suprachiasmatic nucleus, which is in the anterior of the hypothalamus — requires 24.4 hours to complete a full cycle. So it relies on environmental cues, especially light, to synchronize itself.

“We know from research that morning light is critical to our health, well-being, and productivity; it’s the morning light that we’re exposed to that synchronizes our biological clocks,” Stuart Fogel, PhD, professor of psychology at the University of Ottawa and director of sleep neuroscience at The Royal in Ottawa, told Medscape News Canada. Fogel was not involved in the analysis.

“Evening light has the opposite effect, causing further phase delay,” said Lam, adding that modern environments (eg, staying indoors more during the day and using screens at night) exacerbate the disruption.

Adolescents are especially sensitive to these effects, he explained. “They already have problems in winter due to phase-delayed sleep (ie, wanting to go to sleep and wake up later), which is a developmental growth phase,” Lam said.

Further misalignment between the body’s clock and the social clock (ie, the schedule for work, school, etc), which is referred to as “social jet lag,” is worsened by pDST because adolescents are expected to wake up an hour earlier, which increases the potential for poorer educational outcomes.

Fogel agreed that “pDST is especially hard for teenagers; they don’t get exposure to the light needed to send that alerting signal to the brain so they can do well in school. It’s been shown that academic performance slides when [the clock and light exposure] are shifted.”

Enormous Clinical Implications

The policy of moving the clocks in either direction has its fans and critics. But just about everyone agrees that it has ramifications.

“Healthy circadian rhythms that are driven by our biological clocks and sleep are responsible for a vast number of physiologic conditions. The implications from a clinical standpoint are quite enormous,” Fogel said. Changing the clock has immediate effects on mood, cognition, memory, academic performance, and safety. In the long term, it affects cardiovascular health, inflammation-related diseases, and the immune system.

Acute and chronic mental health impacts are the most concerning, Fogel said. “One in five Canadians experiences either seasonal affective disorder or the winter blues. There are significant numbers of people with major depressive disorder. Teenagers especially are at risk for more severe depression symptoms in the winter, and suicide risk increases.”

One factor that is stimulating the conversation between sleep and circadian experts, medical professionals, policymakers, politicians, and the public is that DST only compounds these problems, Fogel added.

The consensus is that standard time is closer to solar time, aligns the master circadian clock, and is best for sleep, mood, and general health, especially in winter. Unfortunately, that does not appear to be the direction in which most provinces are going, at least so far.

“Several countries (eg, the United States, Russia, and Chile) tried pDST in the past, and all of them changed back after the first winter,” said Lam. These countries had widespread public dissatisfaction with dark winter mornings, concerns about children traveling to school before sunrise, and workplace safety issues, which ultimately resulted in reversing this policy decision. “That’s why all sleep and chronobiology societies recommend pST,” he said.

As the clocks are about to change once again in Canada (and permanently in Manitoba), clinical vigilance is needed, Fogel noted. “I hope there’s an awareness that they can expect this to have an impact and know what to look for; that’s the challenge we, as medical professionals, have right now.” The Canadian Sleep Research Consortium and the Canadian Sleep Society have developed important clinical resources on the topic, he concluded.

Lam reported receiving honoraria for ad hoc speaking or advising/consulting or receiving research funds from Asia-Pacific Economic Cooperation, Leading Edge Endowment Fund, BetterUp, Brain Canada, Canadian Institutes of Health Research, Canadian Network for Mood and Anxiety Treatments, Carnot, Eisai, Genome BC, Grand Challenges Canada, Janssen, Lundbeck, Neurotorium, Nova Scotia Health Authority, Ontario Brain Institute, Otsuka Canada Pharmaceutical Inc, Public Health Agency of Canada, Shanghai Mental Health Center, Vancouver Coastal Health Research Institute, VGH & UBC Hospital Foundation, Viatris, and Zydus Pharmaceuticals (Canada). Fogel reported no relevant financial relationships.

Liz Scherer is an independent health/medical journalist who frequently writes for Medscape News Canada.