When I was 17, I got a summer job at my uncle’s factory. He would pick me up every day at 6 a.m. so we could beat the traffic and arrive to the office early. I was excited at the opportunity to make some money and spent the first day getting to know all the nuts and bolts of the job (which in this case were quite literal, since there were bolts all around my desk).
The next few days, however, I found myself feeling less and less excited. Waking up that early, day in and day out, had started to take its toll on me. I felt constantly tired. I wasn’t motivated to learn anymore and I felt like I didn’t even have the energy to socialize. I became a factory zombie, sneaking to the restroom to steal a few precious moments of sleep. No matter how early I tried to go to bed the previous night, I couldn’t get anywhere near the sleep hours I desperately needed before the alarm kicked me out of bed. After a week at the job I came home at 6 p.m. and immediately fell asleep for 12 hours straight. It was at that point that I realized, it was almost like an epiphany, that I will never survive a regular 9 to 5 job. It is a scary revelation to have at the age of 17, when your whole life is ahead of you, but it was as plain as a moonlit sky: I was completely useless without my sleep and my sleep was not easy to master.
Fast forward 20 years and my fascination with sleep has become even stronger. What is it about sleep that makes us feel so alive when we get it and so utterly miserable when we don’t? Why can some people get by with only 7 hours of sleep while others need at least 9? And why, for heaven’s sake, can’t I wake up at 5 a.m. to save my own job?
We don’t have answers to all these questions yet (especially not the last one) but we are learning more and more about the mysteries of sleep. In this blog, I hope to share with you what we have learned about the science of sleep and what happens to our brains and bodies when sleep is taken away.
What determines our sleep pattern?
When we are under an optimal schedule that fits our sleep need, it is hard to see that sleep is not the direct outcome of a simple, straightforward process: We go to bed when we feel tired and we wake up the next day, hopefully refreshed and ready to go. But just like we don’t see the many colors of the sunlight unless we are looking through a prism, under the prism of a restricted sleep schedule, it is suddenly clear that sleep has many more colors dictating its path.
The first thing to know about sleep (and something I wish someone had told me when I was 17) is that it is governed by at least two different biological processes:
The first process controlling our ability to sleep is what we all naturally associate with sleep, which is our sleepiness. The longer we are awake the more tired we become. Typically, after about 15-16 hours of being awake, enough sleepiness (or “sleep pressure”) has built up in our bodies and brains that we feel the need to lie down and close our eyes. This process has been termed process S, for its relation to sleep (not a particularly creative bunch, the sleep taxonomists), and it works somewhat like an hourglass.
The sand in the hourglass is the sleepiness that builds up during the day until we turn the hourglass around and let the sand clear out during the night. When we wake up, the hourglass is turned again and we begin accumulating new "sleepiness-sand" and so on until the next night. How much time it takes to clear the sleepiness determines the amount of sleep each of us needs. Some individuals feel refreshed and ready to go after just 7 hours of sleep and some only after 9. This variability is based on multiple genes, not all of them known yet, and is highly heritable. About 50 percent of our sleep need is determined by our parents (though they might never admit to that when trying to get you out of bed in the morning…).
If process S was the only driving force behind our need for sleep, we would have no problem falling asleep when we are tired, regardless of the time of the day. So, during my factory days I was hypothetically able to change my sleep schedule and fall asleep at around 7 p.m. each night (I was definitely sleepy enough), and in doing so, get all the sleep I needed before the 5 a.m. alarm. But, as anyone who has laid awake in a hotel room after a long, exhausting flight knows, sleep cannot always be summoned at will.
The Sleep-Wake Rhythm
The reason for this sleep stubbornness is the second process controlling our ability to sleep—the circadian rhythm, or simply (and unimaginatively) process C. The term circadian comes from Latin and means "almost a day," referring to our internal, near-24-hour rhythm or our biological clock. The circadian rhythm is involved in many processes that regulate our wake-sleep cycle, including the nocturnal release of the sleep hormone melatonin and the morning release of the awakeness-promoting hormone cortisol. Unlike process S, which tracks our sleep need, process C mostly cares about the time of day, like any good clock would.
But while process S determines how much sleep we need, process C determines when we need it. When our internal clock feels that it is still "daytime," it is physiologically harder to fall asleep even if our sleepiness level is sufficiently high. Now you might ask, how does our clock determine when it is "daytime" and when it’s a good time for sleep? Is it the time the sun rises or sets each day? An hour after or perhaps 30 minutes before? Here, again we find a lot of biological variability across individuals depending on their genetic makeup. About 40 percent of individuals tend to be early types, feeling most alert in the early morning (often referred to as larks) while about 30 percent are late types who feel most alert later in the day (the owls).
These time profiles (or chronotypes) vary in the way their biological clock operates: Early types typically have fast clocks, having internal "days" that are slightly shorter than 24 hours, while late types have internal clocks that cycle a bit slower than 24 hours. If your internal day is shorter than 24 hours you will find it easier to fall asleep relatively early in the night (your internal day would be completed a bit before 24 hours have elapsed) while the opposite is true of someone with a longer internal day. Short-rhythm individuals would therefore tend to go to bed early and long-rhythm ones would retire relatively late. These time profiles, determined by multiple genes, are hard-wired biological mechanisms that we have little control over. The clock is our gatekeeper to precious, revitalizing sleep.
The Rainbow of Sleep Types
Taking both processes S and C into consideration, one can paint a vivid rainbow of "sleep types"—those who retire to sleep early but sleep for a long time and therefore wake up late; those who go to sleep late but wake up early after a shorter sleep; and everything in between. There are just as many long and short sleepers among early types as there are among late types. Getting to know your optimal sleep pattern means understanding both your sleep need (how much sleep you need) as well as your sleep window (when you can get it).
To learn about your own sleep pattern, you can experiment with what I like to call the "sleep reset" protocol. Try to pick a week when you are free to set your own schedule (quarantine could be a great opportunity!) and do the following:
- Avoid alcohol and caffeine after 2 p.m. to unmask your true biological sleep need.
- Keep lights dim in the evening and limit access to LED lights after 9 p.m.
- Go to sleep as soon as you feel tired (even if you're in the middle of something). This will help you figure out the earliest window it is physiologically possible for you to fall asleep.
- Do not use an alarm clock to wake up.
After a few days of catching up on sleep, you will settle into your own natural rhythm and figure out both your sleep need and your ideal sleep timing. In my case, it eventually cost me a nice summer job, but I gained something far more substantial: sweet and refreshing sleep for decades to come.