As many nations prepare to turn their clocks back this weekend to return to standard time—often called winter time—researchers are highlighting the significant health implications of our seasonal time-shifting practices. While the tradition of moving clocks twice a year originated as an energy-saving measure during the First World War and saw a revival in the 1970s, modern scientific evidence increasingly points to the adverse health impacts of these transitions, particularly the shift in spring.
Raymond Lam, a professor of psychiatry at the University of British Columbia and lead author of a recent analysis on daylight saving time, emphasizes that the issue extends beyond merely ending the clock changes. According to Lam, while ending the practice resolves short-term disruptions, the choice of a permanent system will dictate long-term public health outcomes. The study concludes that standard time is the superior option, primarily because morning light is critical for regulating human body clocks, mood, and sleep patterns.
The debate involves a clear trade-off. Permanent daylight saving time could potentially benefit social, recreational, and economic activities by providing more evening light. However, this shift would push sunrise an hour later, forcing many individuals to commute to work and travel to school in darkness during the winter months. Ralph Mistlberger, a professor of psychology at Simon Fraser University, warns that human biological clocks require morning light to remain synchronized with a 24-hour day. Permanent daylight saving time would effectively remove that light precisely when winter mornings are at their darkest.
Conversely, permanent standard time preserves earlier winter dawns, which align more naturally with human circadian rhythms. Exposure to morning light helps counteract the biological clock's tendency to lag, which in turn supports alertness and improves sleep quality. Alexandra Choi, a medical health officer with Vancouver Coastal Health, notes that time policy should be viewed as public health policy. She suggests that if governments move toward permanent daylight saving time, they must proactively plan for the consequences, including monitoring mental health, sleep, and injury rates, as well as ensuring safer morning travel conditions.
Yet deciding whether to keep the practice is only the first step.
Both choices have pros and cons: permanent daylight saving time keeps evenings lighter, which may support recreation, social activity, commuting and some economic activity.
