Day 1
Set Your (Internal) Clock
Let's compare humans to some of our fellow companions on this Earth. Giraffes sleep for less than five hours across the twenty-four-hour day, while lions spend an amazing sixteen to twenty hours resting or sleeping over that same period. The albatross, an enormous airplane of a bird that can travel ten thousand miles in a single journey, can achieve REM sleep while in flight. And hippos? They sleep underwater, unconsciously surfacing while sleeping in order to breathe. Even flowers have an internal clock, coded into their cells, that tells them when to open and close. For as many types of organisms as there are out there, there are types of sleep rhythms.
We humans are fairly boring sleepers-most adults need a minimum of seven hours of sleep per night, and we can't even swim while we're doing it. And perhaps more so than hippos and flowers, we struggle with sleep. A big reason? Our natural sleep cycles are out of whack.
Once upon a time, human sleep cycles were yoked more firmly to the natural world-we woke with the morning light and wound down into sleep as the sun disappeared. Then we discovered fire, and everything went downhill from there. Now we have electricity. Technology. Schedules that are not so much governed by the natural world but by the new digital one we've created. We have emails to return, Netflix to watch, passions to pursue. We're no longer hunter-gatherers who wake and sleep with the sun-we have jobs that get us up early and keep us up late. We're awash in artificial light beaming at us from lightbulbs, phones, and laptop screens long after our distant ancestors would have been deep into their sleep cycles. If our natural biological rhythms were allowed to be the boss of us, maybe falling asleep and waking up would be as effortless for us as it is for the flower.
Is the answer to go off the grid, live in the woods, and sleep and wake with the sun again like our ancient ancestors? Maybe! A really creative research study found that participants who went camping in the Colorado wilderness for a weekend and weren't allowed to use artificial lighting at night (no flashlights, headlamps, nothing) showed a 69 percent shift in their biological sleep/wake rhythm compared to those who stayed home. But my guess is that most people-even those who have sleep struggles-are probably not willing to cut ties with the civilized world completely in order to fix them. We need to figure out a way-within this electrical, digital, twenty-four-hour, interconnected, fast-paced modern world-to stabilize and re-sync our sleep drivers so that we can get the kind of deep restorative sleep we still need as humans.
That's why we're going to start this project of fixing your sleep first thing in the morning. When people have trouble sleeping, a lot of attention gets paid to bedtime. But setting yourself up for successful sleep doesn't start at bedtime, or an hour before bedtime, or whenever you start to wind down for the night. It starts the minute you wake up.
When Do You Wake Up?
Five a.m.? Seven? Noon?
If you're expecting a lecture about the early bird getting the worm, it's not going to come from me. I work with lots of people each year in our sleep clinic at UCSF, working on individualized solutions for their insomnia and other sleep difficulties. And I've rarely told anyone they needed to get up early, or really at any particular time. I don't care what time you wake up. I only care that you wake up at the same time every day.
My youngest son is five years old. I mention that to make clear that I have a natural, unstoppable alarm clock built into my life-even on the laziest of weekends, I couldn't sleep in if I tried. But even if I didn't have this kiddo appearing at my bedside at six o'clock sharp, wanting pancakes and to discuss [insert Marvel Avenger], I still wouldn't try to sleep in on the weekends-not anymore. The luxurious sleepy Sundays of my pre-parenting life are far in the rear-view mirror, and it's because of the data.
If you're like most people (and me, before the science of sleep became my career), you spend your work week running a little short on sleep, then you try to "catch up" on the weekends (or whenever your days off roll around) by tacking on an extra hour or two. This sleep debt that builds up across the week is called "social jet lag." Teenagers are the most striking example of this. There are no teens in my home yet (thank goodness) but I certainly remember being one. Beyond the mood swings and the angst, I remember sleeping in-a lot. Teenagers often experience a shift in their sleep rhythm known as "delayed sleep phase" that increases their biological preference to go to bed later at night and wake up later in the morning. Meanwhile, schools start early-much earlier than teens biologically want to awaken-and it produces sleep debt across the week that compounds into sleeping in on the weekend. "Catching up" on sleep like this makes logical sense: If you're thirsty, drink more water. If you're tired, give your body more sleep. Unfortunately though, for someone struggling with sleep, this strategy often backfires. It not only doesn't work, it can actively work against you.
Your body loves to anticipate your next action or need. It makes insulin in anticipation of a meal, and melatonin in anticipation of sleep. It knows to do these things because of cues in your routine and environment-cues that start the moment you open your eyes, and which accumulate through the day. If your routine is erratic, your body gets confused about what it needs to be doing and how it should be using its resources. No, you don't have to become an automaton doing the same thing every day, eating the same meals, etc.! But figuring out a consistent wake-up time is the number one thing I do with people who come into the sleep clinic. And that's because it's the most powerful regulator of the two natural internal processes that cause sleep.
What Makes Us Sleep?
You have two main "drivers" of sleep: your homeostatic sleep drive and your circadian rhythm. These two natural, internal processes in your body work together (though they are independent) to keep you awake when you need to be awake, and asleep when you need to be asleep. They also need to be in sync for you to get great sleep. When they become dysregulated, you start to run into trouble.
Your homeostatic sleep drive is essentially "pressure" for sleep that builds up the longer you're awake. Picture a balloon. It's flat and empty the moment you open your eyes in the morning. As you go through your day, it gradually begins to inflate, filling up with sleepiness. When it's at this optimal amount-picture a perfectly inflated balloon-you feel the need for sleep. Your eyes get heavy, you climb into bed, and drift off. When you take a nap, you're basically "letting some of the air" out of the balloon, or relieving some of that sleep pressure.
What causes sleep pressure to increase? Well honestly, we aren't 100 percent sure-as much as we've mapped the human brain during sleep, there's still a lot we don't know about sleep even though it's one of the most basic and essential biological processes of the human experience. But one of the leading hypotheses is that our sleep drive is hooked to the buildup of certain neurochemicals-which are byproducts of brain activity. A specific neurochemical responsible for sleepiness is, we think, adenosine. If you've ever taken a science class, you might remember learning about ATP, or adenosine triphosphate, the energy source for all the living cells in our body. While you're awake, adenosine builds up in the brain. As you sleep, that neurochemical drains away. Caffeine, one of the most common ways to keep ourselves awake despite an ever-growing sleep balloon, works because it engages in a biochemical battle with adenosine in the brain. There's basically a fight between the two molecules that breaks out in your brain, and caffeine blocks adenosine uptake by brain receptors. It works really effectively for a while,but when it wears off, you can have a sudden crash of exhaustion as that sleep pressure rebounds right back.
So that's the first important piece: you wake up, that balloon starts to inflate, and once that sleep pressure reaches its optimal level, your body wants to fall asleep. But your homeostatic sleep drive isn't the only thing regulating your sleep cycle. If it were, you might just drop off throughout the day and night whenever that balloon filled up, even if that happened to be in the middle of a meeting or while you were driving. Which brings us to the circadian rhythm.
Your circadian rhythm is, most basically, your "master clock" that governs the rhythm of all your body's processes-including sleep and wakefulness. All of the cells in your body, all of your organs, including your brain, have rhythms. There's an ebb and flow of processes and activity throughout the course of a twenty-four-hour day. That master clock that controls all of this lives deep in an area of the brain called the suprachiasmatic nucleus, or SCN, which is found in the hypothalamus, a small but influential area of the brain that controls everything from the release of hormones, to thirst, to body temperature, and more. It also determines your "alertness rhythm" throughout the day. In general, our alertness tends to spike higher in the morning, dip in the afternoon, rebound slightly, and then wane slowly through the evening until we need to go to sleep.
So how does this "master clock" decide how to regulate us? In two main ways.
The first is internal-your master clock's rhythms are shaped by your genes and the proteins they produce. This is something you don't have much control over. It's written in your DNA. Like a lot of other traits (your hair color, your preference for sweet versus salty, whether you can roll your tongue or not) you inherited a circadian preference from your parents and ancestors. You probably already know whether you're a morning or night person by nature. You can certainly push against your genetic circadian preference, but some people find that more challenging than others. It may always be hard for you to stay up late; or you may manage to shift your wake time earlier because of a job schedule or simply because you want to seize the day, but may always feel sluggish or foggy for a while, like you're fighting your body's preprogrammed settings. That's because, well, you are. (This isn't to discourage you or imply that it's a losing battle-just to realize that there's nothing wrong with you if you do have trouble moving your bed or wake times.)
The second category of factors that influence your circadian rhythm are external. The "arousal systems" in your brain are, at all times, gathering information from your surroundings. Darkness is a huge trigger for sleepiness. First, photoreceptors within the retina sense light or the lack thereof. That information travels through neural pathways in the brain to the hypothalamus, the walnut-sized control center of your nervous system, which notes the waning of the day and pings the pineal gland to begin releasing melatonin, the sleepiness-inducing hormone that's been pilled and bottled and put on shelves all over grocery stores and pharmacies to help the sleep-challenged make it to dreamland. It works in reverse, too: when you're exposed to light (especially direct sunlight), the opposite happens-melatonin release is suppressed.
The external cues that influence circadian rhythm are not limited to daylight-though that's a strong one. There are all kinds of "landmarks" throughout your day that give unconscious yet powerful signals to your brain about where exactly you are in your twenty-four-hour cycle, which allows your body to optimize and prepare for what's next, a process called entrainment. We call these powerful environmental cues zeitgebers, German for "time-givers." The term refers to anything in the environment or routine of a living organism that has the power to change its internal timekeeping clock-in other words, its circadian rhythm. These zeitgebers have the most power over us: Daylight, or the waning of it. When we eat. When we exercise. Temperature. Even social interactions. These elements of your environment or routine become something your body not just responds to, but anticipates. It does this to optimize, to maximize your biological efficiency.
Because of these zeitgebers, your body will produce cortisol in anticipation of you waking up-before your alarm clock even goes off. That way, when your alarm does go off, your energy is already rising; you're ready to wake. It will produce insulin in anticipation of glucose flooding your system during a meal-before you're anywhere near sitting down with your knife and fork. By the time you're chewing and swallowing your food, your metabolic systems are ready to process it into energy and nutrients. And in response to the waning light and dropping temperature of evening, along with other cues in your evening routine, your body will begin releasing melatonin ahead of bedtime, readying your system for slumber.
To sum up: our circadian rhythms are the product of a swirl of factors. They are partially genetically predetermined, partially shaped by our immediate environments and the natural world, and partially regulated by certain elements in our daily routine. The wide variation that we see in human circadian rhythms is interesting-we're not totally sure exactly why people have different genetic variations when it comes to circadian rhythm, but we can certainly take some guesses as to why we might have evolved to have different preferences of awakeness, perhaps having to do with geography, climate, or vigilance and security. Plus, there may be other reasons, not related to sleep, that circadian rhythms vary: circadian clocks play a role in many other processes, including metabolism, which I mentioned above, but also the immune system. One thing sleep and circadian scientists are particularly interested in figuring out right now is how to harness circadian rhythms to positively impact the immune system. For example: because metabolism is hooked to the circadian clock, we suspect that some people may have better responses to medications when taken at certain circadian phases rather than others. There is now an entire field of study surrounding this: chronomedicine. If we can better understand each individual's circadian rhythm, including in their cells and organs, more precisely, we may be able to treat people in a more personalized way.
Copyright © 2022 by Aric A. Prather, PhD. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
