Health Evidence Favors Permanent Standard Time for Sleep
As Canadian jurisdictions consider ending seasonal clock changes, health research indicates permanent standard time better aligns with human circadian biology.
The debate over ending twice-yearly clock shifts in Canada centers on a choice between permanent standard time and permanent daylight saving time, each with distinct effects on sleep, circadian alignment, and health. Several Canadian jurisdictions are moving toward ending the seasonal time change. Permanent daylight saving time keeps evenings lighter but pushes sunrise an hour later, while permanent standard time preserves more morning light and better aligns clock time with human circadian biology.
Dr. Raymond Lam said: "Ending the clock change solves one problem, but it creates another decision: which time should we live on year-round?" The preponderance of health evidence favors permanent standard time. Morning light helps synchronize the body's circadian clock, whereas evening light delays it. Permanent daylight saving time reduces morning light and extends evening light, working against this natural alignment in winter.
Evidence on risks and benefits of each option
Permanent daylight saving time increases evening light but reduces morning light, working against circadian biology. Permanent standard time better aligns with natural light patterns. When daylight saving time begins, it appears associated with increased acute myocardial infarction and fatal traffic accidents, but also with decreased crimes involving physical harm. Within the daylight saving time period, there appear to be fewer all-cause deaths and fewer traffic accidents. Standard time is potentially associated with decreased sleep duration during winter.
An estimated 1% to 3% of people in Canada experience seasonal affective disorder. As many as 15% experience milder seasonal changes in mood, sleep, appetite, and energy. People living farther west within a time zone experience later sunrise by the clock and several adverse health outcomes. Permanent daylight saving time may make it easier to exercise, socialize, or shop after work and school.
Under permanent daylight saving time, possible compensatory 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.
Vulnerable populations and broader implications
Children and adolescents may be particularly vulnerable to permanent daylight saving time due to puberty shifting sleep timing later while school 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.
Lessons from past attempts and future considerations
International experiments with permanent daylight saving time have been reversed. The United States adopted it during the 1974 energy crisis but reversed it within a year. Russia adopted it in 2011 and reversed it in 2014. Chile reversed a national move after its 2015 experiment.
The authors called for more robust research and pointed out the difficulty determining causation. Dr. Ralph Mistlberger said: "Our biological clocks need morning light to stay synchronized with the 24-hour day." Other factors that could play a role include different lengths of days in different latitudes, different health statuses, different behaviour for commuting to work and social commitments, timing of medication, and the nocebo effect fuelled by publicity about negative health effects.
No clear and consistent effects on psychiatric outcomes were identified in the study. Researcher Bullock noted that while epidemiological data from hospital and government records show correlations between time changes and health outcomes, results are still correlational. With so many pros and cons in the debate, and so little solid evidence, the best advice was to 'make the most of the extra sunlight hours'. The authors conclude that the preponderance of health evidence favors permanent standard time.
