By Walt Hickey

Welcome to the Numlock Sunday edition.

This week, I spoke to Olivia Walch, author of the brand-new book Sleep Groove: Why Your Body's Clock Is So Messed Up and What To Do About It.

Olivia’s a good friend of mine and I’ve been hearing about her research and her work for years, and now she’s finally got a whole book diving into why ideal sleep is more than just the eight hours number we hear so much about. It’s a delightful book with all sorts of cool insights that can have major impacts on your life and health.

We spoke about the human body's numerous circadian rhythms, why sleep regularity is more important than sleep duration, and why permanent daylight saving time is a bad idea.

Walch can be found at oliviawalch.com and the book can be found wherever books are sold.

This interview has been condensed and edited.

Olivia, thank you so much for coming on.

I'm so delighted to be here.

You are the author of the brand-new book Sleep Groove: Why Your Body's Clock Is So Messed Up and What To Do About It. It's a really, really fun book. It covers a lot of the science behind sleep and actually has some pretty surprising stuff in there for folks who are interested in their own sleep health.

You have a really interesting story about how you even fell into being interested in the science behind sleep. You did a sleep study at some point in grad school that changed your life, it sounds like.

Well, you knew me before then. We were in college together.

Each diabolically bad at sleeping.

I would give each of us a failing grade — you maybe a lower grade than me. I was bad, but you were exploring new horizons of bad, like with polyphasic sleep.

I tried it once. It was such a bad idea.

Maybe a D, D-minus. I knew when I went to grad school something had to change. I was not sleeping; I was not making new memories; I was getting sick. I got MRSA in college and I wonder all the time, was it because my immune system was like a frail Cheeto trying to hold the door closed to the germs? But at the time, I thought at college, you have to do everything. You have to be in every club and miss no opportunity for an experience. And I now remember no experiences from that time period.

In grad school, I decided I was going to sleep more. I did, but I didn't actually notice that huge of a difference with fewer things filling my schedule, even though I was sleeping more. It was better, but it wasn't that much better. It took a sleep study in which I had to keep a really regular bedtime and researchers were spying on me. They would know if I didn't, because I was wearing a device, ye olde Jawbone, which is not even a thing anymore. For months, I went to bed at 11:30 every single night.

The changes were so profound. I didn't just instantly fall asleep at 11:30, though that did happen. I got faster, I lost weight, skin conditions cleared up. In every dimension, my life was better. And the thing that had shifted was not really sleep duration, but sleep regularity.

You get at this idea early in the book. There's this very common number that everybody associates with the right thing to do about sleep, which is that you should sleep for eight hours. The book goes the next level deeper, looks at some of the other dimensions of sleep, and it turns out that eight hours is good, that's a good thought to keep in your mind, but it's really the rhythm. What is the conceit here? Why are rhythms important when it comes to this stuff?

Our understanding of sleep health is so fixated on duration that there's a creepypasta on Reddit that goes, "Oh, these Russians were kept awake and they went crazy." The creepypasta has always been funny to me because it's like, "Yeah, and after five days of no sleep, they started eating their own organs." (Spoilers for the Russian sleep experiment creepypasta.) Yet we've kept lots of people up for five days and they don't start eating their organs. We have this conception in our minds that losing sleep duration is going to be really bad. It's not good, but it also doesn't make you self-cannibalize after five days of no sleep.

That definition of sleep health is woefully inadequate. The movement in the sleep field is higher dimensional. There are more things that matter to sleep health. There's this big, long list of things. People say you should think about how many times you wake up in the middle of the night, and you should think about how alert you feel during the day.

All of those are great, but they're not memorable. People don't keep two things in their head, let alone five. I'm trying to get people to keep two, which is duration and regularity, as the latitude and longitude of sleep health. You don't say Madrid and New York are close together just because they have the same latitude; longitude also matters. You shouldn't say somebody who sleeps eight hours a night is healthy if they have horrible regularity. That's a case where they are probably pretty far from health, just like New York and Madrid are pretty far from each other.

A lot of this comes down to circadian rhythms. What are they in your view? What kind of bodily processes are governed by them?

The whole shebang. The problem with circadian rhythms is that their UI is terrible. People talk about the circadian rhythm, but that's not really right because circadian rhythms are plural. Sleep is under the subhead of circadian rhythms, but so is everything else in your body: when you're strongest, when you metabolize food, when your immune system peaks, when you repair DNA. There's this real problem. I think that because circadian rhythms are kind of everything, people just say, "You know, the rhythms." This leads to everyone who doesn't study this all day, every day, walking around having no idea what they are and just thinking it's probably the same thing as sleep.

Your body has an internal clock, and it schedules things according to when it thinks you need to do more or less of them. That clock is set by your light exposure, and in modern life, we get light whenever we want it, which is not particularly traditional or natural.

Circadian rhythms developed as a process because we live on Earth, right? We know there's a certain amount of daylight and when certain things should happen, and we evolved specifically to have a circadian rhythm.

Yes. The circadian rhythm is so tuned to Earth that if you put us on a planet with 28-hour days, we probably wouldn't be able to adjust. We would basically continue to have close to a 24-hour period in our rhythms that would continue, even though the sun on this planet would be up and down at different times. It's baked into us, and it's the case that there's just stuff in your body at some times that isn't there at other times. The hormone melatonin, for example. If I made you spit into a tube right now, you would not have melatonin in your spit.

We're speaking in the middle of the afternoon. It's very, very bright outside.

No melatonin. But 10 hours from now? Different story. The thing to imagine is just a bunch of switches in your body getting flipped on and off depending on the time of day, which has massive implications for health, drug efficacy, how you feel, and people have lost their connection to that. Number one, we can have light whenever we want it, so our rhythms are squished relative to where they otherwise would be. But number two, I think we don't have a great way of talking about rhythmic health, which my book tries to address. I'm sure there's much better I can do and other people can do in the future, but this is my first stab at it.

You get at this inflection point where so much of these functions are the result of, if not tens of thousands, then millions of years of evolutionary processes really locking us into a day/night process. Then you have the emergence of electricity, and a lot of your book reflects on how that's actually changed the way our bodies work, in ways we wouldn't ordinarily expect. What are some of those ways?

I would say signs of rhythms having different effects on your body in the winter versus summer. Any study that reports on those, I'm always very cautious about, because I was involved in a study where we looked at Twitter patterns over the course of the year. We wanted to know if people tweeted differently at different times of the year in a way that reflected the sun and circadian rhythms, and we saw this pretty incredible trend where things seemed to really shift around the spring. Daylight saving time is happening then, the sun is changing, so you think, okay, maybe it's related to the sun.

Then we dug a little more closely into the data and saw that the entire effect was just driven by people going on spring break. You would see that people tweeted later when t...