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Time change debate: Is it better to have extra sunlight in the a.m. or p.m.?


In a rare bipartisan moment, the U.S. Senate voted unanimously earlier this month to make daylight saving time permanent. For that to happen, the House of Representatives would need to pass the measure, too. And while many scientists agree, there is no compelling reason to switch the clocks twice a year, the big debate is, which is better, having more sunlight in the morning or in the evening? NPR's Allison Aubrey is here to talk about it with us.

Hey, Allison.

ALLISON AUBREY, BYLINE: Good morning, Rachel.

MARTIN: So I have to admit, there are some clocks in my house I haven't even...

AUBREY: (Laughter).

MARTIN: ...Updated yet, much to my children's chagrin. But it was just a couple of weeks ago we lost an hour of sleep. Clocks sprang forward. It is annoying. But don't our bodies just sort of adjust?

AUBREY: You would think that it's really not a big deal to adjust the clock by one hour, but our bodies kind of tell a different story. What's surprising is that the spring time change is actually linked to an increased incidence of heart attacks and other cardiac events.

I talked to a cardiologist about this, Jay Chudow at Montefiore Health. He has documented this phenomenon. He compared hospital admissions for a type of heart arrhythmia in the days after the time change compared to the rest of the year.

JAY CHUDOW: We found that there were more hospitalizations for atrial fibrillation after the spring time change. I was very surprised because it's just one hour change. Why should it cause this large effect?

AUBREY: He says people who ended up in the hospital with A-fib had other risk factors. They weren't young, healthy people. So the time change wasn't the sole cause but rather the factor that likely put them over the edge.

MARTIN: Right. But still, that is really surprising and disturbing. Or do scientists know why that happens?

AUBREY: Exactly why isn't nailed down. But what has become clear, Rachel, is that our bodies are super sensitive to time. A few years back, three scientists won a Nobel Prize for their work that helped to discover that we have clocks running in literally every cell in our body, some timekeeping mechanism. We are literally timekeeping machines. The first rays of morning light help to reset our clock each day. And with the abrupt change when we spring forward losing that hour, it disrupts our internal clocks in ways that can be harmful. In addition, when much of the nation is tired and groggy on a single day from losing an hour of sleep - it can lead to a lot of distracted drivers on the road.

CHUDOW: Traffic accidents after the time change - there's definitely a signal that there's more of those after we change the clocks, just like there are more workplace accidents and such. And if I can make my own admission, I was involved in an incident on the Wednesday after the time change last week.

AUBREY: He collided with another car. It was not his fault. And while this may seem like a coincidence, it turns out that I was involved in a traffic incident the day of the spring forward change as well.

MARTIN: Wait, what? What happened?

AUBREY: Yeah. Well, I backed into my neighbor's Tesla. He usually parks in his driveway. It was right there behind me. I didn't see it. I was in a hurry, running late. Boom. Thousands of dollars later, I found myself questioning why this happened.

I reached out to the director of the circadian medicine clinic at Northwestern University, Dr. Sabra Abbott. She's a neurologist who researches the impacts of timing on our health.

SABRA ABBOTT: Can you claim daylight savings time was to blame? Probably. I don't know if that would hold up in court. But you probably were sleep deprived. You were probably a little misaligned. And I think that probably played a role in that.


AUBREY: Well, thankfully, no one was hurt in my fender bender. But one study from 2020 found a 6% rise in fatal car crashes after the spring time change. The data are mixed on this. But Abbott says what is very clear is that there are negative health effects linked to shifting the clocks.

MARTIN: OK. So if all of that is true - and we have no reason to doubt it - I mean, it makes sense then to do away with changing in our clocks, right?

AUBREY: There's - yeah. There's a lot of support among, you know, politicians, scientists, people who are just annoyed by this time change. But now the question becomes, which time change could become permanent or should become permanent? Should it be permanent standard time, with more light in the morning, or permanent daylight saving time, with more sunlight in the afternoon, as the Senate has voted to do?

Dr. Abbott says that a lot of sleep scientists don't think the Senate got it right. They argue that permanent daylight savings time is a mismatch with our natural rhythms, since it's that early morning light that resets our clocks.

ABBOTT: One of the consequences of permanent daylight savings time is actually that you end up finding it harder to fall asleep at night because you're getting that light later at night, when it actually pushes time later, and you're getting less of that light in the morning, which makes it harder to wake up in the morning.

AUBREY: In fact, sleep scientists have a position paper on this in favor of moving to permanent standard time so there is more light in the morning.

MARTIN: What was the Senate's argument then, as - in favor of more daylight in the afternoon and early evening instead of the morning?

AUBREY: Well, when daylight saving was first introduced as a concept 100 years ago - the idea - it was it would save energy. But the argument today is that more sunlight in the afternoon makes it easier for people to go out after work and do things, like - and spend money when they go out.

I spoke to Lyle Beckwith of the National Association of Convenience Stores, which lobbied way back in the 1980s to extend daylight saving time to a larger stretch of the year for this very reason.

LYLE BECKWITH: When people come home from work and there's more daylight, they tend to be more active. They go to sporting events. They play softball. They golf. They barbecue. And that translates into an increase in sales of people coming in to buy more water, more Gatorade, more beer, more charcoal, more everything.

AUBREY: He says...

MARTIN: Money.

AUBREY: ...Some stores say - yeah, right? Some sources say they see about a 15%, 20% boost right after the change. Now, Congress may give up on this measure altogether. There are a lot of things happening right now - clearly other higher priority issues. And the House of Representatives has no plan to vote on it now. But if Congress did act, many retailers say they would rather see permanent daylight saving time.

MARTIN: NPR's Allison Aubrey. Thank you, Allison.

AUBREY: Thank you, Rachel.


Rachel Martin is a host of Morning Edition, as well as NPR's morning news podcast Up First.
Allison Aubrey
Allison Aubrey is a correspondent for NPR News, where her stories can be heard on Morning Edition and All Things Considered. She's also a contributor to the PBS NewsHour and is one of the hosts of NPR's Life Kit.