Permanent Daylight Saving Time Could Harm Sleep and Mental Health, Analysis Says

Canadian health researchers led by Raymond Lam examined the health trade-offs of adopting permanent standard time versus permanent daylight saving time and conclude that permanent standard time better aligns with human circadian biology. With several Canadian jurisdictions already moving to year-round daylight saving time and a U.S. House bill proposing national adoption, the team warns that keeping daylight saving time year-round would delay winter sunrises by about an hour (e.g., Toronto’s latest winter sunrise shifting from 7:51 a.m. to 8:51 a.m., Calgary from 8:40 to 9:40), forcing more people to commute and attend school before natural morning light. Morning light is central to synchronizing internal clocks, so later solar time risks reduced sleep, worsened mood, impaired learning and productivity, and could blunt an evidence-based treatment for seasonal affective disorder.

The authors acknowledge drawbacks to permanent standard time - earlier summer sunrises and earlier winter sunsets - but argue these are easier to mitigate with measures like blackout curtains and sleep-health education. By contrast, permanent daylight saving time would demand broader interventions: improved street lighting, reflective gear for children, later school start times, flexible work schedules, increased morning lighting in institutions, and clinical monitoring for sleep and seasonal mood problems. They urge governments to track outcomes including school absenteeism, mental-health and sleep issues, injuries, physical activity and cardiovascular events, and to analyze effects by age, geography, socioeconomic status, rurality and shift-work exposure. Lam et al. published their analysis in CMAJ (2026).