Is daylight saving a detriment to our health?

Less light in the mornings is argued by some to be linked with an increased risk of a variety of conditions...
24 October 2023

Interview with 

Beth Malow, Vanderbilt University Medical Center


Sunrise or sunset over sea


So, what impact might meddling with the clocks - and our own body clocks - have on our health? Beth Malow is the director of the Sleep Disorders Division at Vanderbilt University Medical Center. Beth argues that it is time to abolish the changing of clocks and adopt permanent standard time in the United States. Chris Smith began by asking her about the impact that changing clocks can have on our health...

Beth - I like to think of it as two different effects: there's an acute effect, meaning the abrupt change, and then there's more of a long-term chronic effect. Even though it only seems like an hour shouldn't be that disruptive, we can see an uptick in the numbers of strokes and heart attacks and people who just feel off balance/off kilter. We also see car accidents go up and medical mistakes that people make in the hospital, and it's worse when we spring ahead in March maybe because we're also losing an hour of sleep. There is a more long-term effect that lasts basically eight months of the year when we're on daylight saving time. And again, people would think, 'Well it's one hour. I get used to it, I get over it and I'm done.' But we need morning light to wake up and feel good. It boosts our mood, it helps us actually get to sleep easier the following night, and all of that is disrupted when we shift the clocks.

Chris - What effect is that going to have on my physiology?

Beth - Come March, we're going to have that light taken away from the morning and moved to the evening. First of all, it affects our mood. We give light boxes for seasonal affective disorder, a form of seasonal depression in the morning. That's when we need our light to help us wake up, get going, and feel better. And then we also see that there are increases in different medical conditions. So, for example, we see more obesity, more problems maintaining your weight, we see more diabetes, we see more problems with heart disease. And this is all felt to be related to either not getting as much sleep as we need because we're not getting that morning light and not getting to bed at a good hour, or what a lot of scientists call being misaligned, being out of sync with the outside world because now we're artificially moving our clocks an hour later.

Chris - Why do we do this, then? Why do we subject ourselves to these clock changes? Arguably, if you've got the sorts of effects that you are seeing, would we not be better off sticking to one time?

Beth - You make a great point. A lot of it is inertia: doing the same thing we've been doing for a long time. We have to choose between being on daylight saving time all year round and being on the standard time all year round. And even though, as a sleep health expert, I can make an argument for staying on the standard time all year round, there are arguments that have been made for being on daylight saving time, particularly having that light later in the day for golf games and shopping and various other things. If we keep doing what we're doing, we don't have to have to choose between one or the other, which can be very challenging politically.

Chris - But it sounds like there might be a case medically to keep on one time and choose the right time all year round based on what you've been saying?

Beth - Yes. And I also think there have been some studies that have pointed to increased productivity when you're on standard time or when you're getting more light in the mornings.

Chris - Some people have argued that also, human behaviour being what it is, that the original thoughts about having more time with light at certain times of the day than others just don't stack up in terms of how our behaviour is changed. The morning rush is quite a compressed activity early on in the day and is therefore safer than the afternoon journey home. And that includes schools coming out, people coming home from work and so on. And so actually, people are arguing, having more time at the end of the day might be a better option than more time at the beginning of the day with daylight because perhaps people would be more active, also there would be more light to light that journey home and keep the younger people safer?

Beth - I think it goes both ways. With the abrupt change, there's going to be some change in the safety issue and you can't really get away from it. It's going to affect one side or the other. In terms of what you do when you move your light for eight months of the year to the afternoon, I think you could argue it again both ways. You could look at the kids who are really sleepy and sleep deprived and have very early school start times so it's dark when they're trying to go to school as opposed to the afternoon where at least when they're getting out of school it's lighter. It's hard to know. And I think it also depends on where people live. I know that the traffic accident data has been one of the hardest to interpret. The health effects are a lot stronger for standard time.

Chris - So that's presumably what you would wish for if you could wave your magic wand and we stuck to one time zone, no time changes indefinitely thereafter. That's what you'd vote for?

Beth - Yeah, I would vote for standard time. I feel like it's the healthier choice overall and improves mental health, physical health and at least some aspects of safety and productivity.

Chris - Wouldn't you miss, though, that extra hour in bed that you get in the autumn when you know that you don't have to get up quite so early? It's a fallacy, but it it's still good, isn't it?

Beth - I know what you're talking about. It makes you want to hit the snooze alarm several times. I think the other thing I try to impress on people is that it's going to be darker in the winter. We can't make the days longer and even if we were to stay on year daylight saving time, that is not going to make us have endless summer or longer days. We're kind of stuck. And to me, I would rather have that light in the morning to help me get up and get to bed at a decent hour. I hope other people would like to have their light then as well.


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