Across much of the United States and Canada, daylight saving time begins Sunday at 2:00 a.m. local time. Most people will turn their clocks forward an hour, trading an hour of sunlight in the mornings for more daylight at the end of the day. When it ends, clocks move back an hour nearly eight months later to provide more morning light in the darkest days of winter.
But British Columbia will switch its clocks for the last time — moving to permanent daylight saving time. The change was supported by “more than 90% of British Columbians,” Premier David Eby said. “The way that we live our lives now in the modern era, having an extra hour of sunlight at the end of the day, whether it’s the winter or the summer, makes a big difference for people,” Eby told NPR’s Adrian Ma on All Things Considered.
Experts in sleep medicine and public health, however, warn against making daylight saving permanent.
“Daylight saving time has been shown to have a lot of negative effects,” said Emily Manoogian, a senior staff scientist at the Salk Institute and an executive member of the Center for Circadian Biology at UC San Diego. She noted the U.S. tried permanent daylight saving in the 1970s for one year and quickly reverted after people faced dark mornings, children walked to school in the dark, and there were a few fatal car accidents.
Eby acknowledged health concerns but argued residents are accustomed to dark winter mornings. “We’re on the very western edge of the time zone and so we have dark mornings anyway,” he said. “People really want that hour at the end of the day.”
Why daylight saving can be harmful
Biology favors permanent standard time because our internal circadian clocks — which govern sleep-wake cycles and many cardiac and metabolic processes — are synchronized to daylight, Manoogian explained. Light is the strongest cue for coordinating behavior: when sunlight reaches the eyes in the morning, it signals the brain and body to wake and prepare for the day. Without morning light, the body has a harder time recognizing morning, making it difficult to wake up.
Evening light similarly delays sleep. When it remains bright late into the evening, people tend to go to bed later and then struggle to wake the next morning, leading to later bedtimes, poorer morning alertness, and disrupted daytime cognition and metabolism. These shifts can have broad public health impacts and are associated with increases in car accidents, heart attacks and strokes in the week after the start of daylight saving time.
“We know that sleeping, eating, getting light at the wrong time is a huge risk for cardiometabolic disease,” Manoogian said. “Every medical and scientific society would argue we should never go to daylight saving time. It was originally created to try to save energy, [but] evidence has shown it does not save energy.”
A study by Stanford researchers published in the Proceedings of the National Academy of Sciences in September 2025 found that switching clocks twice a year carries a significant public health toll, increasing strokes and obesity. The study concluded that switching permanently to standard time would yield the largest health benefits — including far fewer strokes and obesity cases — while permanent daylight saving reduces those harms but not as much as standard time.
“When we can realign better to our environment, we get better sleep,” Manoogian said. “We have lower risks of almost any chronic disease you can imagine — cardio-metabolic, cancer, even depression, bipolar disorder.” She emphasized that the health benefits of standard time are substantial.
Easing the transition
If you’re concerned about the effects of daylight saving time, Manoogian recommends steps to reduce the impact:
– Get morning light: If the sun is out when you wake, expose yourself to it. If it’s dark, turn on bright lights in your home to simulate morning light.
– Prioritize sleep: Aim for seven to nine hours of sleep each night and keep a consistent sleep schedule.
– Keep meal times regular: Eating during a consistent window aligned with your active daytime can improve metabolic health. Waiting an hour or two after waking to eat and restricting meals to an 8–10 hour window can help.
– Shift kids gradually: Move schedules by about 20 minutes per day over several days to help children adjust to the time change.