“Many of my colleagues have signed on to petitions and statements from various kinds of medical organizations saying that we have to go into permanent standard time, that that is better for your health. That statement's always bothered me because that's a very strong statement to make from a public health standpoint. And so, if you're going to make a statement like that, have good evidence.”
Atmosphere with Emily Gracey · October 2026
Context
Zeitzer, a sleep and circadian researcher, was asked what is best for health. He says the strongest evidence is only that the spring clock change carries small risks, and that the case for permanent standard time rests on good theory rather than much data. His own modelling found some effect, but less than people hoped and varying by location.
Transcript
…state does it. And so, yeah, so it kind of started back then. And back in the 70s, they tried getting rid of standard time, moving to permanent daylight time, and people hated that. So there's a market history, but it's definitely something that people have opinions about, like what it should be.
They do. And, you know, even in my house, it's like we argue about this. But I mean, I can guess what your argument is because I hear this from most scientists. But can you tell me like what from our circadian rhythm and health-wise, what is the best possible situation?
Well, that's, it's, it's actually more complicated than you'd want. So many of my colleagues have signed on to petitions and statements from various kinds of medical organizations saying that we have to go into permanent standard time, that that is better for your health. That statement's always bothered me because that's a very strong. Statement to make for a public health standpoint. And so, if you're going to make a statement like that, have good evidence. Right now, the best evidence is that the time switch in the spring is associated with negative effects and the time switch in the fall is not. And the time switch in the spring, again, not always is it associated with negative effects, but many studies have found that. And basically, the idea is that, well, when you move an hour and you lose an hour of sleep, such as happens in the spring, that's associated with negative outcomes and negative outcomes like increased risk of heart attacks and car accidents, strokes. Those are kinds of the main things. When you look at it, though, the evidence indicates that the risk to any individual is vanishingly small. It is just when you have 350 million people doing it on the same…
Right.
That's finite. Like, I wish I could change that. It'd be really popular if I could change how much light was there, but I can't. But I can just, you can just change when it's occurring. Well, does it change exercise, which would imply that it might change health? So do people exercise more if you…
There's so much to unpack here. And that doesn't even factor in like. I'm a mother, so my thought keeps going back to like kids and especially like school in the morning and bus stops and dark bus stops. But then also, like, is school starting too early? Like, is it about our schedules? And should…
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