Bay Area scientists find even more reasons to hate daylight saving time →

Published by SFGATE

Daylight saving time is not only jarring but also unhealthy, according to a new study by Stanford scientists.

The findings published Monday in the Proceedings of the National Academy of Sciences show clear biological costs to the fall-back, spring-forward routine, which Californians have already voted to abolish.

The new study says the current schedule, where almost all states adopt daylight saving time for eight months each year, disrupts our circadian rhythms and can lead to more strokes and obesity. The research adds to prior reports of spikes in heart attacks, injuries and traffic crashes after people lose an hour of sleep when daylight saving time starts in March. 

“This is the first real piece of evidence that staying in permanent standard time would be better, from a biological perspective, than either permanent daylight saving time or the current shift twice per year,” said Jamie Zeitzer, Ph.D., a Stanford psychiatry and behavioral sciences professor and the study’s senior author. “Until now, we’ve just had theories.”

Zeitzer and his colleague found major health benefits to ending the spring forward from standard time to daylight saving time. Using mathematical models and data from the Centers for Disease Control and Prevention, the researchers estimated that sticking with standard time all year would prevent about 300,000 strokes annually and lead to 2.6 million fewer people with obesity nationwide.

The key reason our seasonal time shifts are so damaging is how they impact our circadian rhythms, the internal clocks that regulate most body processes and are vital to a functioning immune system and sleep cycle. Out-of-whack circadian rhythms are linked to a wide range of health issues, including stroke and obesity. One way circadian rhythms get scrambled is by being exposed to light at the wrong time: morning light can help body clocks stay synchronized, while evening light can slow them down. 

“I think the best analogy is that your circadian clock is acting in the body like a conductor acts in an orchestra,” Zeitzer said. “With a weak conductor, it might still sound fine in the violin section or the flute section, but the audience hears a cacophony. And that’s what happens in the body, too, with everything just a little bit off.”

The scientists looked at the three possible time policies based on how they affect light exposure and impact circadian rhythms and overall health throughout the year. They found permanent standard time was best overall, permanent daylight saving time was second, and our current practice of switching back and forth was the absolute worst. 

The findings varied a bit based on region and between night owls and morning larks. Those who like to stay up later (you know who you are) bear the greater negative health effects of the seasonal time switching. 

Despite widespread dislike for the more-than-century-old institution of daylight saving time, the best alternative option remains up for debate. Health organizations like the American Academy of Sleep Medicine support standard time, in favor of more morning light. Meanwhile, bills proposing permanent daylight saving time, which means more evening light, hit Congress nearly every year, but have yet to pass.

“The way they modeled this study is genius,” said Joanna Fong-Isariyawongse, a neurologist at the University of Pittsburgh who focuses on sleep medicine but wasn’t involved in the study. “We know that we should end the twice-yearly shifts, but there’s this argument about which way we should go. They tried to show us which approach is best.”

California could in fact adopt standard time, joining Hawaii and most of Arizona. In 2018, California voters passed Proposition 7, allowing the state Legislature to end the seasonal switching between times — but so far, bills there have failed.

Zeitzer acknowledges limitations to his study, such as not accounting for erratic sleep schedules or light habits, like late-night phone scrolling. He also cautions there are other factors that must be considered in a policy change, like the economic effects. 

But for some scientists, a change is a no-brainer. 

“I think there is a great health argument for ending daylight saving time,” said Karin Johnson, a neurologist at the University of Massachusetts Chan Medical School who was not involved in the study. “Hopefully, policymakers will add this study to their data and listen to science and listen to the public.”