The debate over winter time or summer time is gaining renewed attention as researchers warn that keeping daylight saving time all year could affect sleep, mood and the body’s internal clock. Although lighter evenings appeal to many people, experts say permanent standard time may better support human health by preserving natural morning light.
Many countries continue to change their clocks twice a year, moving them forward in spring and back in autumn. The practice shifts daylight hours on the clock rather than changing the amount of daylight available, and it has remained controversial despite repeated attempts to end seasonal clock changes.
Seasonal time changes were introduced in several countries during the First World War as a way to conserve energy. The practice returned in many places during the 1970s, but researchers have increasingly questioned its effects on sleep and overall health, particularly following the spring change, when people lose an hour of sleep.
However, ending the twice-yearly adjustment would not settle the debate entirely. Governments would still need to decide whether to adopt permanent standard time or permanent daylight saving time, a choice that could influence people’s daily routines and long-term health.
“Ending the clock change solves one problem, but it creates another decision: which time should we live on year-round?” said Raymond Lam, a professor of psychiatry at the University of British Columbia and lead author of a recently published analysis in the Canadian Medical Association Journal examining the health effects of daylight saving time.
The analysis argues that eliminating seasonal clock changes could reduce short-term disruption, but the permanent time system would also matter because of its longer-term effects on sleep and the body’s circadian rhythm, the internal system that regulates sleep and wakefulness.
The central issue is the relationship between daylight and the body’s internal clock. Light helps regulate when people feel awake and when they become sleepy. Morning sunlight signals to the brain that the day has begun, helping synchronise the body’s natural rhythm with the 24-hour day.
Ralph Mistlberger, a professor of psychology at Simon Fraser University in Canada, said morning light is particularly important because the human biological clock tends to run slightly longer than 24 hours. Regular exposure to light in the morning helps keep it aligned with the natural day-night cycle.
“Permanent daylight saving time moves that light an hour later just when winter mornings are already darkest,” Mistlberger said.
Under permanent daylight saving time, clocks would remain one hour ahead of standard time throughout the year. Although this would provide more daylight during the evening, it would also delay sunrise on winter mornings. People starting work or school early could spend more of their morning commute in darkness.
Permanent standard time, by contrast, keeps clock time more closely aligned with the sun. Earlier winter sunrises can provide morning light that supports alertness, sleep quality and mood, according to the researchers. The analysis therefore supports keeping standard time throughout the year if seasonal clock changes are abolished.
The choice is not without trade-offs. Later sunsets under permanent daylight saving time may make it easier for people to exercise outdoors, socialise or take part in other activities after work. Longer, brighter evenings may also benefit some businesses and parts of the leisure economy. These advantages help explain why the idea of keeping summer time all year remains attractive.
However, the researchers argue that evening convenience should not be the only consideration when governments decide how to set clocks. A time system affects more than leisure schedules. It can also influence sleep patterns, school journeys, workplace routines and road safety during the darker months.
Alexandra Choi, a medical health officer with Vancouver Coastal Health, described time policy as a public health issue. She warned that governments choosing permanent daylight saving time should prepare for its potential consequences before the first winter under the new arrangement.
That preparation, she said, should include measures to make morning travel safer, flexibility around start times where possible, and monitoring of sleep, mental health and injuries.
The debate is relevant beyond Canada. In Finland, clocks will move back one hour on Sunday, 25 October 2026, returning the country to Eastern European Time. The change is part of the European Union’s shared system, under which clocks move forward in March and back in October. Finland supports ending the seasonal changes, but EU rules currently prevent individual member states from abandoning the system on their own. A European Commission study on the effects of changing the clocks is expected to be completed by the end of 2026.
The new analysis does not mean that every person will experience the same effects, nor does it remove the practical and economic questions governments must consider. It does, however, add to the body of research favouring permanent standard time on health grounds. The decision facing policymakers is not simply whether people prefer brighter evenings or brighter mornings, but how a permanent clock system would affect sleep, daily routines and public safety across the year.
