In the U.S., the first Sunday in November brings temporary joy—an extra hour of sleep—followed by months of what can feel like unending darkness. It’s all worth it, though, for those long summer nights. Right?
Maybe. Some health experts argue we should scrap daylight saving time in favor of permanent standard time. Yet just this week, the House of Representatives passed a bill which, if it makes it through the Senate, would make daylight saving time permanent. This would mean no more changing the clocks twice a year and more evening daylight—and even darker winter mornings. So is this manipulation of the clocks actually good for human health? The answer is far more nuanced than you might think.
Should standard time be the standard?
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
“The position that we take is that permanent standard time is the best option from a human biology standpoint,” says Muhammad Rishi, a critical care and sleep medicine expert at Indiana University School of Medicine. He was lead author on a 2024 position paper from the American Academy of Sleep Medicine that advocated for permanent standard time over daylight saving time.
When it comes to discussions over daylight saving time, there are three popular policy options: keeping the current system of seasonal clock changes, instituting permanent standard time, with no clock changes, or using permanent daylight saving time, in which the clock stays “sprung forward” all year around.
But in chronobiology, the scientific study of biological rhythms, there are three different “clocks” that can become misaligned: the solar clock, determined by Earth’s rotation around the sun; the biological clock, the body’s internal timing system, also called the internal or circadian clock; and the social clock, or “the clock on the wall,” Rishi says.
“Our systems work best when we are trying to follow the solar clock,” he says. “The problem is that the social clock does not always follow the solar clock.”
When they fall out of sync, researchers call that social jet lag.
Daylight saving adds to social jet lag because it shifts the social clock an hour ahead of the sun. Morning light is the strongest natural cue that resets your biological clock each day, Rishi says. Darker mornings make it harder for your internal clock to stay aligned with the social clock. And unlike actual jet lag, in which the body adapts to its new environment over a few days, Rishi says there is no evidence that the body ever fully adapts to the shift in daylight.
“You are trying to follow a clock that’s incompatible or inconsistent with the solar clock locally,” he says.
Over the past few decades, numerous studies have linked social jet lag to worse health conditions, such as shorter sleep, type 2 diabetes, metabolic disease, obesity and cardiovascular disease.
“It’s important to note that at the individual level, the increase [in risk] is really very small,” says Jamie Zeitzer, a neurobiologist and co-director of the Center for Sleep and Circadian Sciences at Stanford University.
“It’s at the population level,” he says. “When you have 350 million Americans on the same day losing an hour of sleep and moving a time zone, that’s when you see these increased risks.”
One oft-cited study is a 2019 paper published in the Journal of Health Economics in which researchers compared people living at different longitudes within the same time zone. Because everyone in the same time zone used the same social clock, the main difference was solar time. They found that people living farther west within the time zone—who thus experienced later sunrises and sunsets—had shorter sleep duration, as well as a higher prevalence of health problems such as obesity, diabetes, heart disease and breast cancer.
“These effects are the consequences of a long-term-exposure to circadian rhythms disruptions,” the study authors concluded.
A better wake-up time
From a social jet lag standpoint, most sleep medicine and chronobiology researchers agree that keeping the current system is worse than permanent daylight saving time, Richi and Zeitzer say. But both of these increase the gap between the solar clock and the body’s internal clock, which has been linked to poor health outcomes.
Rishi, who lives in Indiana, says that “if we were to have daylight saving time during the winter, the sun would not come up in Indianapolis until after 9 A.M. My kids’ school starts around 7:15 in the morning. That would mean that the kids will be in school for at least two hours before the sun comes up.”
Zeitzer notes that, like anything at the intersection of science and society, the situation is nuanced.
“From a circadian perspective, I think it’s pretty clear, but it definitely has not been integrated in with the behavioral effects that you have with this, and I think that’s problematic,” he says.
Instead of seeing a law change get pushed forward now, Zeitzer says he would like to see more research into understanding the overall health and behavioral effects of the different options.
