When is daylight saving time, and how does losing an hour of sleep affect our health?

This Sunday, most Americans will move their clocks one hour ahead for daylight saving time. Losing one hour of sleep can make the morning alarm sting just a little more, but the effects of daylight saving can stay with us for weeks.

Here’s how switching up the clocks affects our body.

Our body keeps track of when to wake up and go to sleep based on an internal clock known as our circadian rhythm. Sunlight helps keep that clock ticking.

“When our clocks are artificially advanced by one hour, it makes our schedule essentially one hour out of sync with our biological clock,” said Joseph Takahashi, chair of neuroscience at UT Southwestern Medical Center’s O’Donnell Brain Institute. Takahashi identified the first gene known to control circadian clocks in mammals with his lab in 1997.

Pushing clocks ahead in the spring cuts both ways. It’s darker in the morning, which makes it harder to wake up; and it’s brighter in the evening, which makes it harder to fall asleep, according to Dr. Debra Atkisson, a psychiatrist and associate professor at the Burnett School of Medicine at Texas Christian University.

Atkisson added that losing one hour of sleep due to daylight saving can cause a “sleep debt” that takes a while to adjust to.

“A lot of people are a little more … foggy in the morning after daylight saving time,” she said. “And I don’t mean the immediate morning after. I mean for weeks after.”

A 2020 research paper looking at fatal motor accidents in the United States from 1996 to 2017 found that spring daylight saving time increased the risk of such accidents by 6%. The shift to daylight saving time has also been associated with increased risk of heart disease.

Daylight saving time is observed in almost every U.S. state, except for Hawaii and most of Arizona. It’s also not observed in U.S. territories, including Puerto Rico, Guam and American Samoa.

The U.S. Senate unanimously passed the Sunshine Protection Act last March, which would make daylight saving time the permanent time zone, as opposed to standard time, the time zone we’re in from November to March.

The bill stalled in the House and expired at the end of Congress’ last session last year, but Florida senator Marco Rubio reintroduced the legislation last week.

Researchers like Takahashi worry about making daylight saving time permanent, saying it could leave our internal clocks out of sync. “It would be even worse than what we’re on now, where we’re switching back and forth,” he said.

Another issue with daylight saving, Atkisson said, has to do with expectation.

During the summer, she encourages parents to phase their kids back into an earlier sleep schedule at least a month before school starts, so they get used to the routine. But kids and adults are expected to adjust to daylight saving time the morning after the switch and go to school and work like nothing happened.

Atkisson tries to reduce her stress load as much as possible by not planning major meetings in the two weeks after daylight saving, and tries to give herself a little extra time in the mornings. She recommended that people be kinder to both themselves and others in the weeks following the clock switch.

“I think if everybody would do that, be a little kinder [and] gentler,” she said, “it would make the transition easier.”