Several Canadian jurisdictions are moving toward ending the twice-yearly clock change, but a new analysis published in CMAJ ( Canadian Medical Association Journal ) https://www.cmaj.ca/lookup/doi/10.1503/cmaj.261089 argues that eliminating the clock change is only half the decision: governments must also decide whether to adopt permanent standard time or permanent daylight saving time. Both choices have trade-offs. Permanent daylight saving time keeps evenings lighter, which may support recreation, social activity, commuting, and some economic activity.
But it also pushes sunrise an hour later, leaving more people waking, travelling to school, and commuting to work, in darkness during the winter. Permanent standard time preserves more morning light and better aligns clock time with human circadian biology, although evenings become darker earlier.
“Ending the clock change solves one problem, but it creates another decision: which time should we live on year-round?” says lead author Dr. Raymond Lam, professor of psychiatry at the University of British Columbia (UBC), Vancouver, BC. “The health evidence points to standard time, largely because morning light matters for our body clocks, sleep, and mood.”
Weighing the trade-offs
Major sleep and chronobiology organizations recommend permanent standard time. The authors note that morning light helps synchronize the body’s circadian clock, while evening light delays it. Permanent daylight saving time, therefore, works against circadian alignment during winter by reducing morning light while extending evening light.
“Our biological clocks need morning light to stay synchronized with the 24-hour day,” says Dr. Ralph Mistlberger, professor of psychology at Simon Fraser University, Vancouver, BC. “Permanent daylight saving time moves that light an hour later just when winter mornings are already darkest.”
The effects may be especially important for mood and sleep. An estimated 1% to 3% of people in Canada experience seasonal affective disorder (SAD), while as many as 15% experience milder seasonal changes in mood, sleep, appetite, and energy. The authors also point to geographic studies showing that people living farther west within a time zone — where sunrise occurs later by the clock — experience several adverse health outcomes.
Children and adolescents may be particularly vulnerable because puberty naturally shifts sleep timing later while school still starts early. Other potentially affected groups include shift and early-start workers, public transit users, pedestrians and cyclists, and people living in rural or lower-income communities with poorer lighting and transportation infrastructure.
The authors acknowledge that permanent daylight saving time has advantages. Longer evening light may make it easier to exercise, socialize, or shop after work and school.
“The attraction of permanent daylight saving time is easy to understand. People like more light after work and school,” says Dr. Patrick Baylis, associate professor at the Vancouver School of Economics at UBC. “But those evening benefits have to be weighed against evidence linking later solar time with less sleep, lower productivity, and worse educational outcomes.”
International experience also provides cautionary examples. The United States adopted permanent daylight saving time during the 1974 energy crisis but reversed the policy within a year amid opposition to dark winter mornings and concerns about children travelling to school before sunrise. Russia adopted permanent daylight saving time in 2011 and reversed it in 2014 after public dissatisfaction. Chile similarly reversed a national move to permanent daylight saving time after its 2015 experiment.
The authors of the Analysis emphasize that whichever policy governments choose, its effects should be monitored. Under permanent daylight saving time, possible measures include safer roads and pedestrian infrastructure, later or more flexible school and work start times, increased morning light exposure in schools and workplaces, and monitoring of sleep, mood, injuries, and other health outcomes. Permanent standard time would require fewer measures, mainly addressing earlier evening darkness in winter and earlier dawn in summer.
“Time policy is a public health policy,” says Dr. Alexandra Choi, medical health officer with Vancouver Coastal Health. “If governments choose permanent daylight saving time, they should plan for the consequences before the first winter — from safer morning travel and flexible start times to monitoring sleep, mental health, and injuries.”
The authors conclude that the preponderance of health evidence favours permanent standard time.
“We have focused for years on whether to stop changing the clocks,” Dr. Lam says. “The more important question now is what happens the morning after we stop.”
Canadian Medical Association Journal
Literature review
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Analysis of health impacts associated with adopting permanent standard time or permanent daylight saving time to inform policy in Canada
5-Oct-2026