Standard time beats daylight time for health

Clinical takeaway: Ask patients with seasonal low mood or poor sleep about natural light soon after waking, and consider bright light therapy for seasonal affective disorder. The costs of year-round daylight time appear better established than its evening benefits. 

The US House of Representatives passed a bill in July that would make daylight saving time permanent, and the Senate now has it. Hawaii, most of Arizona and five US territories already skip the change and stay on standard time. Ending the switch may spare patients the sleep loss and injury risk tied to each spring change, but jurisdictions still have to choose between a permanent clock an hour ahead and one fixed on standard time. 

Sleep and chronobiology societies have called for standard time. It keeps winter sunrise earlier, which fits the body clock better and cuts pre-dawn waking and travel. Permanent daylight time keeps evenings lighter, but it delays dawn for patients who wake, commute and start school in the dark. A policy analysis from Canadian researchers extends that case by weighing the circadian, mental health and economic evidence for each clock. 

Jurisdictions weighing permanent daylight time against permanent standard time would see sunrise and sunset both come an hour later under daylight time. In six Canadian cities, that would put the latest winter sunrise between 8:35 a.m. in Montréal and 9:40 a.m. in Calgary. The earliest winter sunset would fall between 5:11 p.m. and 5:41 p.m., which may favor evening leisure and retail activity. 

An hour of later sunset was tied to nearly an hour less sleep per week within US time zones. At Florida schools straddling a time-zone line, adolescents scored higher in math and reading with an extra hour of sunlight before school. Puberty shifts sleep timing later while school start times often stay early. The authors argue daylight time would widen that mismatch, called social jet lag. 

The authors urge jurisdictions that choose daylight time to plan mitigation up front: safer road and pedestrian infrastructure, later or more flexible school and work start times, and more morning light in schools and workplaces. They also recommend preparing clinicians to monitor for more sleep disruption and seasonal mood symptoms. Under either clock, they want school absenteeism, mood presentations and road injuries tracked, with data broken out by age, socioeconomic status and shift-work exposure. 

"The attraction of permanent daylight saving time is easy to understand. People like more light after work and school," says Patrick Baylis, PhD, associate professor at the Vancouver School of Economics at the University of British Columbia. "But those evening benefits have to be weighed against evidence linking later solar time with less sleep, lower productivity, and worse educational outcomes." 

Source: Lam RW, et al. (2026 Oct 5) CMAJ. Analysis of health impacts associated with adopting permanent standard time or permanent daylight saving time to inform policy in Canada