Why Doctors Don’t Like Daylight Saving Time

If you’re bumbling through your mornings in the dark right now because we just set our clocks ahead an hour for daylight saving time, you might be thrilled at the prospect of seasonal time changes becoming a thing of the past.

The U.S. Senate proposed to do just that this week, passing the Sunshine Protection Act in a rare unanimous vote. If the legislation passes the House and gets signed by President Biden, it will take effect in November 2023 and permanently leave our clocks where they are right now — in the “spring ahead” setting for daylight saving time.

Is Daylight Saving Time the Answer?

Doctors and sleep experts are thrilled at the idea of eliminating seasonal time changes. But they also think that making daylight saving time permanent will leave clocks stuck in the wrong place.

“I would love to stop seasonal clock change but have us stay on standard time,” says Marie-Pierre St-Onge, PhD, the director of the Sleep Center of Excellence at Columbia University Irving Medical Center in New York City.

Standard time, when our clocks are set back an hour in the fall, is better aligned with the body’s circadian rhythm, or natural sleep-wake cycles, Dr. St-Onge says. Our biological clocks are hardwired for us to wake when it’s light and sleep when it’s dark, and standard time offers more sunshine in the morning and less at night.

Daylight saving time does the opposite, and provides more sunshine in the evenings. This, sleep experts say, runs counter to our biological clocks in ways that can be harmful for our health.

“Current evidence best supports the adoption of year-round standard time, which aligns best with human circadian biology and provides distinct benefits for public health and safety,” the American Academy of Sleep Medicine (AASM) said in a statement after the Sunshine Protection Act passed.

Health and Safety Problems Associated With Time Change

Each spring, the abrupt change in clocks is associated with a wide range of public health and safety problems, including an increase in heart attacks and strokes, mood disorders, and motor vehicle crashes, the AASM notes.

For starters, it makes it harder to sleep. In that first week after we set clocks ahead for daylight saving time, we may lose an average of 40 minutes of sleep a night, according to a study published in the Journal of Applied Psychology. This is also associated with an uptick in workplace injuries, the study found. With the switch back to standard time in the fall, however, we don’t lose sleep or become more accident prone.

Fatal accidents also become more common after the spring transition to daylight saving time, according to a study published in Current Biology in January 2020. This study found a 6 percent increase in fatal traffic accidents during the week after the springtime shift to daylight saving time. Eliminating this seasonal time change could prevent 28 fatal crashes a year, the authors concluded.

During the first week after the shift to daylight saving time, the risk of heart attacks climbs 3 percent, according to a study published in Sleep Medicine. There isn’t any change in heart attack rates with the fall transition to standard time, the study found.

If the misalignment between our biological clocks and our sleep-wake cycles is made permanent by the adoption of year-round daylight saving time, we may see increased rates of a wide variety of health problems associated with circadian rhythm disruptions, including type 2 diabetes, obesity, and dementia.

“Daylight saving time increases our morning exposure to darkness, when we need to wake up, and evening exposure to sunlight, when we should be winding down for sleep,” says Ilene M. Rosen, MD, an associate professor and sleep researcher at the Perelman School of Medicine at the University of Pennsylvania in Philadelphia.

“The daily cycle of light and darkness is the most powerful timing cue to help synchronize the body clock,” Rosen adds, “So our circadian rhythm is disrupted by being exposed to more light in the evening during daylight saving time, which negatively impacts the health and safety of Americans.”