Canadian health researchers are urging governments to choose permanent standard time if they end the twice-yearly clock change, warning that permanent daylight saving time could worsen sleep and mental health. Their analysis compares the two year-round systems, not whether seasonal clock changes should end.
Professor Raymond Lam of the University of British Columbia, the study’s lead author, said the evidence favors standard time because morning light helps regulate body clocks, sleep and mood. The paper appears in the Canadian Medical Association Journal.
Winter Mornings Drive the Health Concern
Several Canadian jurisdictions have moved to permanent daylight saving time after dropping seasonal clock changes. Yukon adopted the policy in 2020. British Columbia followed in March 2026, with Alberta and the Northwest Territories doing so a month later. The United States House of Representatives passed a bill in July to establish permanent daylight saving time nationwide, but the measure remains before the Senate.
The researchers say the choice of clock setting matters because permanent daylight saving time would move sunrise an hour later. In Toronto, the latest winter sunrise would be 8:51 a.m. under daylight saving time, compared with 7:51 a.m. under standard time. In Calgary, the corresponding times would be 9:40 a.m. and 8:40 a.m.
That additional morning darkness could leave people traveling to work or school before sunrise, while placing more daylight in the evening. The team says the change could affect sleep, mood, learning and productivity, especially for people with sleep difficulties or early schedules.
Simon Fraser University Professor Ralph Mistlberger, a co-author, said biological clocks need morning light to stay synchronized with the 24-hour day. He said permanent daylight saving time would move that light later during already dark winter mornings.
Researchers Compare the Two Systems
The analysis says accumulated evidence favors permanent standard time because it keeps clock time more closely aligned with human circadian biology. The researchers also point to seasonal mood concerns. An estimated 1-3% of Canadians experience seasonal affective disorder, while as many as 15% experience milder seasonal changes in mood, sleep, appetite and energy.
Seasonal depression is more common in Canada during winter. Poor sleep, low energy and impaired concentration are prominent symptoms among adolescents. Morning bright light therapy is an evidence-based treatment for seasonal affective disorder. The authors say delaying natural morning light could weaken a circadian signal.
The researchers acknowledge that permanent standard time has drawbacks too. Earlier summer sunrises could trouble people prone to waking early, while earlier winter sunsets could limit evening outdoor and commercial activity. They suggest modest responses such as blackout curtains and public education about sleep health.
Permanent daylight saving time, they say, would require broader measures for darker winter mornings: better street lighting and sidewalks, reflective equipment for children, later school start times, flexible work, and more morning lighting in schools and workplaces. Clinicians could monitor sleep disruption and seasonal mood symptoms.
Monitoring Would Track the Effects
The scientists recommend that governments monitor whichever system they adopt. They name absenteeism, mental health and sleep problems, workplace and road injuries, physical activity and cardiovascular events for observation. They also call for results to be examined by age, geography, socioeconomic status, rurality and shift-work exposure, to identify unequal effects.
Co-author Dr. Patrick Baylis of the University of British Columbia said people value having more light after work and school. But he said those evening benefits must be weighed against evidence linking later solar time with less sleep, lower productivity and worse educational outcomes.
The researchers recommend permanent standard time on health grounds and say governments should track consequences after choosing a system.
For related reporting on decisions with public consequences, see the CLARITY Act debate, water-system security concerns, and Canada’s trade uncertainty. These are separate stories and do not concern the clock-setting analysis.
Read the source analysis report for the researchers’ account.
