NPR News & Classical Music
Play Live Radio
Next Up:
Available On Air Stations

How Daylight Saving Time Changes More Than Clocks

Howard Brown repairs a clock at Brown's Old Time Clock Shop in Plantation, Florida. (Joe Raedle/Getty Images)
Howard Brown repairs a clock at Brown's Old Time Clock Shop in Plantation, Florida. (Joe Raedle/Getty Images)

Most of the country switched their clocks back an hour over the weekend, ending daylight saving time. And even though one hour might not sound like a lot, it has a noticeable impact on people’s health and routines.

“In the long term, this one hour cumulatively can really have effects on our health,” says Erik Herzog, professor of biology and neuroscience at Washington University in St. Louis.

Herzog, who’s in favor of avoiding daylight saving time and staying on standard time instead, tells Here & Now‘s Jeremy Hobson the positive effects of daylight saving time in the fall — feeling like there’s more time in the day, for example — are short-lived.

“What we see is, in the data, when we ‘fall back,’ there’s about one day during which folks are enjoying that extra hour of sleep,” says Herzog, also president of the Society for Research on Biological Rhythms. “That effect lasts for about one day.”

Interview Highlights

On why a one-hour time change makes such a difference

“When we live on standard time, our bodies have an internal clock called a circadian clock that has evolved to synchronize to that schedule of the sun rising and setting every day. When we mess with that clock — for example, when we’re on shift-work schedules or we fly across time zones — we can often feel jet lag or even worse, certain forms of depression and other bad health consequences.”

On how long it takes to overcome adverse health effects that come with a time change

“It has to do with how big a time shift we’re trying to accomplish. So if you fly one time zone east, generally it’ll take folks one or two days to get on the new schedule. If you fly one time zone west, folks actually adjust even a little bit faster for reasons that are still not totally clear. But when it comes to daylight saving time, or the ‘fall back,’ there’s really nothing in the environment that changed, it’s just the clock on the wall that changed. And so, how do we accomplish that shift when in fact our environment hasn’t changed at all?”

On how “springing forward” impacts our health differently than “falling back”

“What’s interesting is that, in the spring when we ‘spring ahead,’ there’s bigger effects and they last for longer, that are mostly detrimental. So things like three days of increased heart attacks, increased chances of being in a car accident. During daylight saving time, there’s now pretty good evidence that we’re actually chronically more sleep deprived than when we’re on standard time.”

Jill Ryan produced and edited this interview for broadcast. Jack Mitchell adapted it for the web.

Copyright 2021 NPR. To see more, visit