When is daylight saving time and how does it affect our health?

This Sunday, most Americans will move their clocks one hour ahead for daylight saving time. Losing one hour of sleep seems fleeting, but its effects can stay with us for weeks.

Here’s how changing clocks affects our body.

WHY AM I TIRED AFTER DAYLIGHT SAVING?

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, chairman of neuroscience at UT Southwestern Medical Center’s O’Donnell Brain Institute.

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.

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.

WILL DAYLIGHT SAVING BE PHASED OUT?

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.

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.