Editor’s Note (11/5/21): This story from October 29, 2020, is being republished ahead of November 7, when daylight saving time will end this year and clocks will be turned back one hour.
It’s nearly that time of the year again: the end of daylight saving, when Americans push their clocks back and rejoice at the gained hour of sleep—or mourn the lost hour of sunlight in the afternoon.
This system’s twice-a-year transitions have become increasingly unpopular. Scientists have been calling attention to the damaging effects of the time changes—which include a general reduction in mental and physical well-being, as well as a potential increased risk of serious complications, such as strokes and heart attacks, soon after the shifts. There is also evidence of increases in traffic fatalities and harmful medical errors shortly following when clocks are moved forward in the spring.
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.
In many countries, this might be the one of the last instances in which people make the adjustment. Governments around the world have been in discussions about scrapping the seasonal clock changes and sticking to one time—either permanent standard time or permanent daylight saving. In the U.S., many states are considering, or have already passed, legislation to adopt one of the two. Hawaii and most of Arizona decided to adopt just standard time more than 50 years ago. Last year the European Parliament voted to abolish the time shifts, but the member states of the European Union have yet to agree on how to implement the decision.
Beth Malow, a professor of neurology and pediatrics at Vanderbilt University, spoke with Scientific American about the health effects of this timekeeping practice and what should replace it.
[An edited transcript of the interview follows.]
The end of daylight saving time is fast approaching. Generally speaking, how disruptive are the transitions to and from daylight saving to physical and mental well-being?
There’s a lot of variability in what people experience. Some people have shared with me that, for example, they might have a child with autism, and for two or three months after the transition, they feel like things are just not right with their child’s sleep. People also tell me they just feel out of sync for a while. Other people may deal with the change more easily. It’s similar to when we travel [from the U.S.] to Europe. Some people are affected by jet lag more than others.
The one thing I will say is that people think, “Well, it’s only an hour, so it’s not a big deal. It’s kind of like traveling from Nashville, [Tenn.], to New York [City]—going from Central to Eastern time.” But [daylight saving] really isn’t that. It’s a misalignment of your biological rhythms, or circadian rhythms, for eight months out of the year.
You wrote a commentary in JAMA Neurology last year that discusses some medical complications—such as cardiovascular problems and stroke—associated with the transitions. Can you talk a bit about how daylight saving changes can increase the risk for these kinds of events?
We don’t know the actual mechanism because these are epidemiological studies, where there are large numbers of people, and [researchers] observe the stroke rate or heart attack rate increase the week after [the time change]. The predominant increase has been with the switch from standard to daylight in March. We think that what’s triggering that [increase] is either the loss of an hour of sleep or the circadian misalignment, where you’re off sync when you move the clocks an hour ahead. Whenever we disrupt sleep or disrupt our circadian rhythm, it can cause increases in inflammatory markers and our stress response—and we know that can take a toll on the heart and the brain.
You mentioned that not everybody is affected equally by the time changes. Are some people more vulnerable than others? And if so, what is known about why they are more at risk?
Some people definitely seem to be more vulnerable. I think age is one factor. As we get older, our circadian rhythm or just our ability to deal with sleep deprivation is affected. So younger people do better than older people. People with underlying conditions oftentimes struggle more—people with neurodevelopmental conditions [such as autism] or degenerative conditions such as Alzheimer’s or other forms of dementia will be more sensitive.
Some of us are morning people, and some of us are night owls. Our ability to deal with being up later or earlier, depending on the time change, can affect us as well. All of those can make a difference. I don’t think we know enough yet about what factors influence our ability to adapt. I think there are probably also some genetic factors that we’re not aware of that would make people more susceptible.
I imagine people are experiencing negative effects every year. Is there any research looking at the kind of long-term versus short-term impacts of these changes?
I think, in reality, by October or November, we’ve gotten over the March transition. It’s probably, in most people, maybe, at most, several weeks. What’s more of an issue is: you almost have a chronic circadian misalignment—or things are just off-kilter for eight months of the year. That’s how I would look at it. When you’re in standard time, the sun at noon is, in most places, right above your head—you’re really aligned. When you’re in your daylight saving time for eight months of the year, you’re an hour off, and you're getting not enough light in the morning and too much light at night. And that gets worse as the summer approaches—as the days get longer, and you’re getting light into the evening, when your body should be getting less light so that it can get ready for bed. In the morning, as we start getting into the fall, it gets darker when you’re in daylight saving time.
This year is a bit different, given that there is the COVID-19 pandemic, which itself has been associated with sleep disturbances, and the forthcoming U.S. presidential election. Do you think that these things will make the transition back to standard time particularly disruptive for some people?
Yes and no: Yes, in that we’re all dealing with a higher baseline level of stress. When you add in the stress of transitioning from one time to another, you’re going to have more stress. On the other hand, I think the advantage right now [is related to] the reason that we didn’t really pay attention to [the shift] very much in March, [which was that] most of us were working from home, and we had more control over our sleep-wake cycles than we normally did. For example, I didn’t have to wake up at 6 A.M., so I didn’t notice as much whether it was dark or light. The more that we can control our schedules, [the easier] it’s going to [be]. In some ways, the pandemic has made it easier because we’re not as rigid in our time zones.
I will say that I’m excited about people getting an hour more sleep on November 1, because I think that will bode well for being rational at the polls. Regardless of which side you’re on or what’s going on in your individual state with your Senate races, at least Americans will know that their mind and their ability to vote in a rational way is optimized because they’ve gotten that extra hour of sleep.
There have been efforts both in the U.S. and elsewhere to abolish these yearly time changes, either by adopting permanent daylight saving or sticking to standard time alone. Do you agree with these efforts?
Most people agree that we need to get rid of this transition back and forth. I personally am an advocate for permanent standard. The reason I am is because I look at light as really important for our well-being, our mood and our sleep. Getting enough light, especially in the winter, is critical. If we have permanent daylight saving time, I worry that come May, June, July, we’re getting too much light too late in the evening. Then we have trouble falling asleep because we don’t make [enough] natural melatonin, which requires it to be dark. To me, the beauty of the permanent standard is: you have your light in the morning in the winter, when you need it, and you have your dark in the summer, when you need it. [Studies have] shown that if you’re on the eastern side of the Central time zone versus the western side of the Eastern time zone, you’ll actually get more sleep because you have that extra hour of light in the morning and don’t have that extra hour of light at night.
The American Academy of Sleep Medicine just came out with a support on permanent standard time, and there are a lot of different groups that have come out in favor of permanent standard time from the health standpoint.
Some countries and U.S. states already do not observe daylight saving time. Have researchers studied those areas to see how that arrangement has worked out for people who live in them?
I have not seen those studies; I’d like to see those studies. I don’t think we know enough about Hawaii and [most of] Arizona, where they have opted out of daylight saving time. But I’m really glad you brought that up. It’s important to readers to know that a state can opt out of daylight saving time. In order to go to permanent daylight saving time, we actually have to have an act of Congress, which could be a pretty heroic effort right now, in our politically divisive time.
I would say anyone who believes that we should get rid of the transition and just go to one [time], that would be a very strong argument for going to permanent standard. Then I think we can do some of those studies you’re talking about, because we can compare rates of illness, sleep and car accidents before and after they make that switch.