Canadian health researchers are urging the country to choose permanent standard time over permanent daylight saving time if it ends the twice-yearly clock change, warning that darker winter mornings could harm sleep and mental health.
Several Canadian jurisdictions have been moving toward permanent daylight saving time after eliminating seasonal clock changes.
Yukon adopted the policy in 2020, followed by British Columbia in March 2026 and Alberta and the Northwest Territories a month later.
The United States House of Representatives also passed a bill in July to establish permanent daylight saving time nationwide, although the measure remains before the Senate.
“Ending the clock change solves one problem, but it creates another decision: which time should we live on year-round?” said University of British Columbia’s Professor Raymond Lam, lead author of the study.
“The health evidence points to standard time, largely because morning light matters for our body clocks, sleep, and mood.”
Professor Lam and colleagues examined the health consequences of the two possible permanent systems rather than the broader question of whether seasonal clock changes should be abolished.
They concluded that the accumulated evidence favors permanent standard time, which keeps the clock more closely aligned with human circadian biology.
This distinction, according to the team, becomes particularly important during winter.
Permanent daylight saving time would push sunrise an hour later. In cities such as Toronto, for example, the latest winter sunrise would occur at 8:51 a.m., compared with 7:51 a.m. under permanent standard time. In Calgary, the corresponding times would be 9:40 a.m. and 8:40 a.m.
The extra hour of morning darkness could leave people traveling to work or school before sunrise, while shifting more daylight into the evening.
The change could have consequences for sleep, mood, learning and productivity, particularly among people who already have difficulty sleeping or who must follow early schedules. The reason is rooted in the body’s internal clock.
“Our biological clocks need morning light to stay synchronized with the 24-hour day,” said Simon Fraser University’s Professor Ralph Mistlberger, co-author of the study.
“Permanent daylight saving time moves that light an hour later just when winter mornings are already darkest.”
The analysis also highlights concerns about seasonal depression.
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, and symptoms including poor sleep, low energy and impaired concentration are particularly prominent among adolescents.
Bright light therapy in the morning is an evidence-based treatment for seasonal affective disorder.
By delaying natural morning light, permanent daylight saving time would act in the opposite direction, potentially weakening an important circadian signal.
The researchers acknowledge that permanent standard time also has drawbacks.
Earlier summer sunrises could cause problems for people prone to waking early, while earlier winter sunsets could limit evening outdoor and commercial activity.
They recommend relatively modest measures such as blackout curtains and public education on sleep health to address those effects.
Permanent daylight saving time, in contrast, would require a much broader set of measures to reduce the effects of darker winter mornings.
These could include better street lighting and sidewalks, improved traffic safety, reflective equipment for children, later school start times, flexible work schedules and increased morning lighting in schools and workplaces. Clinicians could also be prepared to monitor sleep disruption and seasonal mood symptoms.
The scientists recommend that governments closely monitor the consequences of whichever system they choose, including school absenteeism, mental health and sleep problems, workplace and road injuries, physical activity and cardiovascular events.
They also call for the data to be examined by age, geography, socioeconomic status, rurality and exposure to shift work so that unequal effects are not overlooked.
“The attraction of permanent daylight saving time is easy to understand,” said co-author Dr. Patrick Baylis, a researcher at the University of British Columbia.
“People like more light after work and school.”
“But those evening benefits have to be weighed against evidence linking later solar time with less sleep, lower productivity, and worse educational outcomes.”
The paper appears today in the Canadian Medical Association Journal.
_____
Raymond W. Lam et al. 2026. Analysis of health impacts associated with adopting permanent standard time or permanent daylight saving time to inform policy in Canada. CMAJ 198 (34): E1335-E1340; doi: 10.1503/cmaj.261089