Circadian rhythms deep dive part I

Use the sun to improve your health, fitness, and sleep (a sane, highly useful take on circadian science).

Post summary

• Circadian rhythms—the 24-hour cycles humans evolved to function under—are a hot topic in health and wellness right now.

• But the field of circadian science also contains a lot of junk science and advice.

• We spoke with Lynne Peeples, author of the new book The Inner Clock, to get the most helpful, high-impact information around circadian rhythms.

• You’ll learn:

  • Why modern life works against our natural circadian rhythms.

  • The link between circadian rhythms and disease, depression, and decreased athletic performance.

  • Low-effort, high-impact ways to improve your circadian biology. This advice can help you lose weight, sleep and perform better, and more.

  • How Lynne would design an ideal day around circadian rhythms.

  • What to do if you ever work late nights (which can be hell for your circadian biology).

  • Myths about circadian rhythms (this one was fun).

  • Lynne’s insane personal experiment around circadian rhythms.

  • The health impacts of daylight savings time.

Housekeeping

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• ICYMI:

  • On Wednesday, we featured three lessons in mental toughness. These are pulled from conflict zones and CIA training. A shift in thinking makes all the difference.

  • On Friday, our Gear Not Stuff video featured my favorite cold-weather exercise gear. We also explained 7 laws for building the perfect outdoor exercise system (so you can use gear you already have better).

Audio/podcast version

• Listen to the podcast/audio edition here.

  • P.S., I usually embed the podcast from Apple or Spotify, but I’m going to start linking to the episode’s page on Two Percent, which links to more platforms to listen on.

The post

If you’ve spent more than 60 seconds inside internet wellnesstan, you’ve probably encountered information about circadian rhythms.

Circadian rhythms are like the sun: so hot right now.

It’s an apt comparison because circadian rhythms are intimately linked to the sun and how our bodies evolved in 24-hour-ish night and day cycles. We’d be up and active in the sunshine, then rest when the sun went down.

Thus, nearly every cell in our bodies evolved to have a clock. These clocks turn on or off processes that influence our physical and mental health, performance at work and in workouts, etc.

Think of circadian rhythms as a symphony: At certain times of the day-night cycle, your body collectively must hit certain notes at the same time to cue important processes. For example, metabolism, hormone release, sleep, appetite, digestion, temperature, etc.

But in modern life, we throw these clocks off. And when these clocks get disoriented, it’s like our conductor drank a bottle of Jack Daniels before going on stage. The symphony gets all out of wack.

Simple decisions we make every day determine whether our conductor is drunk or sober and leading our bodies to hit the right notes.

It’s a fascinating new field that we’re learning a lot about—three scientists won the 2017 Nobel Prize in Medicine for their work in circadian science.

Yet science moves slow. So when interesting new fields in health and wellness emerge, they get a lot of attention. And human attention naturally gravitates to what’s new.

The problem is that many take that excitement and over-index on the topic, and we start to think the new thing is the one big thing we’ve been missing.

Hence, we’re now told we must do all sorts of stuff to get our circadian rhythms in order. Like, go outside at a specific time when the sun is at a specific angle and stare into that burning ball of gas for a specific amount of time until our eyeballs burn just as bright. Or that we must wear wacky, light-filtering glasses. Or time our every action with the precision of a Swiss Watch. Etc.

The good news: Getting your circadian symphony in order doesn’t have to be so exhausting.

To understand what’s worth your time and efforts, I spoke with Lynne Peeples. Lynne and I went to grad school together in New York City, where she spent time expanding her already giant scientific knowledge base in the city’s various labs and libraries while I mostly wrecked my circadian rhythms in late-night bars.

Lynne has a new book called The Inner Clock: Living in Sync with Our Circadian Rhythms.

It’s the smartest dive into circadian science I’ve found.¹

The Inner Clock is packed with fascinating, useful information.

And I love that Lynne went all in on reporting this book. FFS, she lived in decommissioned underground nuclear bunker for 10 days just to experience what happens when you completely remove light/dark cycles and nuke your circadian biology.

This post is a conversation with Lynne.

I learned a lot and also left the conversation feeling like I had actionable, painless information that I could use to eat, sleep, and live better.

Lynne’s dive into circadian science all started in the locker room of the Seattle Mariners.

Let’s roll …

On the fascinating way Lynne stumbled into this project

Michael

So … the Mariners locker room?

Lynne

I moved back to Seattle 10 years ago, and I was invited to a press tour of Safeco Field, where the Mariners play. I was just excited to stand at home plate, but they also took us into the team’s locker room. And they’d installed this crazy new lighting system where they could adjust the intensity and the color of the light to help the players' circadian rhythms to energize them before games and calm them down after games so they could sleep and get up again for the next day’s game.

I nerded out on that. And I also grew up in Seattle. We had very gloomy winters and short days for a good portion of the year. I had crazy differences in mood during summer versus winter when it was darker. I’d spend so much more time indoors and never felt great.

Then I went to college in Minnesota—which was freezing, but the winters were always so much brighter, with clear sky, sun, and sun reflecting off the snow. I felt better.

I wondered if circadian science could explain some of my issues over the decades—and if there were some potential strategies I could use to feel better and do better.

The mismatch between circadian biology and modern life

• Takeaway: Modern lighting and indoor work has led us to experience less light in the day and more at night, which works against the circadian rhythms we evolved to have.

Michael

So the Mariners basically had to install this complicated lighting system to offset the fact that the team is living in the new, built environment where their players aren’t necessarily getting a normal cycle of day and night.

Is this analogous to us? Is there a mismatch between how humans evolved to be exposed to the sun and dark and the lives we now live?

Lynne

Humans evolved outdoors. We saw daylight during the day and darkness at night. We didn't have artificial lights. We primarily evolved at the equator where we had 12 hours of light and 12 hours of darkness each day. We were active during daylight hours. We slept when it got dark for the most part.

Artificial lighting has changed how we live, and not just in the sense that we’re exposed to less sunlight and more artificial light.

For example, it was very unlikely that we went out in search of a midnight snack. Because that wasn't safe. You could get killed. So we mostly ate during daylight hours.

Today we spend 90 plus percent of our time indoors. Our artificial light doesn’t come close to comparing to what nature provides outdoors. And we can now eat at all hours of the night—we stretch the time we eat into the night right before bed, and that can throw off our circadian rhythms.

Then we also have daylight savings time and time zones, which change our clocks to be out of alignment with the sun. We can quickly travel internationally, work jobs at night, and more.

So all these factors in modern society pull us away from the natural cycles we evolved for.  

Michael

So does this explain why I feel like shit when I eat late right before bed or have to take a trip that crosses multiple time zones?

Lynne

Pretty much.

A ranking of what’s messing with your circadian rhythms

• Takeaway: You’re probably getting too little light in the day and too much at night, and eating too late.

Michael

What are the biggest disruptors for most people most of the time? Can you rank them, or am I asking too much?

Lynne

Number one, I think it's less daylight in the day and too much artificial light at night, due to indoor lifestyles. Losing that contrast between light and dark is probably number one.

Number two would be our food consumption. Stretching meals into the night. Or, I’d say, calorie consumption, because drinks count too—which people like to forget. That glass of wine at night counts, especially because alcohol is particularly impactful at night. That’s an easy number two.

Third—and this doesn’t count for everyone, but it’s important—would be the 24-hour modern lifestyle.

Think of shift work. If you get an Amazon package in the middle of the night, it means that there's a worker out there managing or delivering that package in the middle of the night. Of course, we’re not going to get rid of doctors, nurses, and firefighters doing their jobs 24/7.

But many jobs put people in a position where they're working outside of the hours during which their body is primed to be up and sleeping at the wrong times.

Michael

Just how screwed are shift workers who work the graveyard?

Lynne

Oh, gosh, I hate to say this, but it's pretty bad.

But because we're understanding it better, we're also learning how to mitigate those consequences. Research out of Harvard shows that many chronic health risks associated with shift work are likely linked to metabolism.

So having a shift worker eat during daylight hours even if they work at night seems to help. Studies show this may mitigate many risks.

Even using a happy lamp, a lamp that mimics sunlight, can be useful in certain situations. I sent a happy lamp to a friend who was on a ship in the Arctic at a time when it was dark 24/7 there, and he said it totally helped him.

Health impacts of circadian rhythms

• Takeaway: A disrupted circadian rhythm seems to influence our physical and mental health. But the extent of this influence depends on how disrupted your rhythms are, and it’s important to know that the science is evolving.

Michael

How much does this matter for health? What did you find out about the physical and mental health impacts of disrupted circadian rhythms?

Lynne

The science is definitely evolving. It’s a long list that keeps growing because we know that circadian rhythms drive so many important processes, where doing the right thing at the right time matters. There are a lot of bi-directional things going on.

For example, if the timing of hormones and various other cyclical signals cycles are off—not there when we need them or there when we don’t need them—a lot of things happen that are linked to inflammation, chronic disease, and mental health issues.

Circadian rhythms definitely seem to matter for metabolism and digestion, and disruption can increase your risk of diabetes, obesity, and heart disease. And the data is piling up for links with disrupted circadian rhythms speeding up dementia and Alzheimer’s.

Maybe more obvious is mental health conditions like seasonal affective disorder. We have the most evidence on this. For example, epidemiological studies show that people at higher latitudes are at greater risk of mental health issues with the short days in the winter.

But let me also say that this is an active area of research and much of this is very new. We’re still learning a lot and figuring out how much this all matters.

How to design an ideal circadian day

• Takeaway: It doesn’t have to be too taxing: Wakeup when your body wants, go outside a bit, and don’t eat too late.

Michael

Ok, let me put you on the spot and ask what the ideal day looks like. If you were to design a circadian-friendly day, what would that look like?

Lynne

First let me say that everyone’s circadian rhythms are different. We call this chronotype. Some people’s circadian rhythms are longer—a bit over 24 hours. Some are shorter—a bit under 24 hours. And your chronotype usually determines whether you’re a morning person or a night person.

I can simply my approach to three things.

1. Sleep: If I'm really being true to my clocks, I would not have an alarm clock go off. I'd wake up when my eyes open, when my body's body clocks are ready to start the day on their own without an alarm. When I went to bed that night, I’d turn down the thermostat. The sleep science suggest most people sleep better in the mid-sixties.

2. Light: I’d try to get some daylight after waking, assuming the sun has come up. I’d get some time outside. I’m fortunate to work by a big window, so I’m sitting in daylight often. But I’d also go outside for breaks and get some daylight. At night, I’d try to keep my house rather dim. I'm a complete nerd and have electric candles all over my place that I turn on to create a low-lit, cozy scene. I’d also not have lights all over my room and try to sleep in a room that’s fully dark.

3. Meals: I’d wait an hour or two to eat breakfast. Then I’d proceed with my work day. At lunch, I’d eat outside. I have a balcony that I’d eat lunch at. Then I’d continue on with work. I would have my last meal and stop eating at seven, which would give me a few hours of not eating before bed because I usually go to bed around 10 or 10:30. If I was meeting people for drinks, I’d do happy hour and not drink late.

You’ll probably be pretty solid if you do some version of these things based on your own natural sleep schedule daily.

Circadian myths

• Takeaway: Blue light gets too much attention and we’re often told to avoid it at the wrong times.

Michael

There’s a ton of info online right now about circadian rhythms. We hear all sorts of hyper-specific advice. You did a ton of research for this book. What advice out there do you feel like is a myth?

Lynne

Probably the overplay of blue light. Blue light is the wavelength of light that our circadian system is most primed to listen to.

However, you see a lot of pushing of blue light blocking glasses and people saying you should wear them all day. But that’s not necessarily the answer.

During the day, you actually want those blue light wavelengths. So that's an issue in and of itself because it could backfire.

At night, maybe blue light blocking glasses have their place. But if you still have bright overhead lights on, you can still be setting your clocks up for trouble. So I think it's probably more powerful just to dim the lights and try to live in a dimmer, warmer-colored environment at night.

Lynne explains what she learned living in an underground nuclear silo for 10 days (?!), as a grand experiment in circadian rhythms gone wrong

• Takeaway: If you’ve ever traveled internationally and gotten jet lag, you may have experienced some of the same awful symptoms Lynne did.

Michael

The bunker. The nuclear bunker. TELL US ABOUT THE NUCLEAR BUNKER YOU LIVED IN.

Lynne

I thought it would be good to figure out my own rhythms and really experience some of this myself.

So I needed to find a place I could hide from daylight and other people. It was hard to find that place. I determined I’d probably need to be underground. I found a decommissioned nuclear missile bunker in Arkansas—the Titan II Nuclear Missile Complex—that a guy named GT Hill had bought from the government and retrofitted into an AirBNB. He’s an amazing dude. Quite the character.

So I went down there for 10 days. I needed it to have no cues about what time it was, and it was hard to set it up to be totally time-free. It was a luxurious bunker. Digital clocks were everywhere. So GT and I taped over those.

I set all the lighting to dim red, which doesn't affect the circadian rhythms the same. And then I decked myself out with tons of gadgets, measuring everything from temperature and heart rate to glucose levels and light exposure.

The hardest part was being lonely for 10 days, but it was also kind of nice not to have any obligations and to hide away from a phone and everything for all those days.

But I felt pretty miserable starting halfway through. It was symptoms like jet lag. And it got pretty intense. My stomach was off, my head was off, my mood was up and down, I’d feel sweaty at weird times. I was confused sometimes.  

I was worked with scientists to look at that data and then correlated that with how I was feeling.

And sure enough, when I was feeling out of whack, my circadian rhythms fell out of sync with each other. My heart rate rhythm and the temperature rhythm changed. I had less coordination.

They not only shifted off of the sun cycle, but they also dampened and became discordant. And that translates to not feeling so good. Over the long term, that can translate to chronic mental and physical health issues.

The downsides of daylight savings

• Takeaway: Kill daylight savings.

Michael

We just had the daylight savings time switch over. What did you learn about that?

Lynne

The science is pretty clear that by going on daylight savings time, we're taking an hour of that critical morning light and attaching it on to the end of the day where it shouldn’t be. So it's throwing us out of alignment with the sun.

Scientists are rather unanimous that we should be on standard time year round. Clock changes are basically giving us jet lag, or clock whiplash. Regardless of the time on our wall clocks, we have fewer hours of daylight in the winter. The best thing to do is get outside more.

Have fun, don’t die, get outside more this winter.

-Michael

P.S. Get Lynne’s book if you want to go deeper on this topic.

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1. Such is the value of a great science journalist who goes out into the world and speaks to all the top minds in the field, synthesizes that disparate information, and gives you the consensus. I’m biased, but I usually find books by science journalists to be broader and better than those by researchers, who tend to study very narrow fields.