Entrepreneur and researcher Dan Pardi delves deep into the need for sleep in this second instalment of his three-part series.
In the previous article in this series, we talked about the 2-Process Model of Sleep Regulation, which helps us to understand how sleep and wake are controlled across a 24-hour period.
The first of these two processes – sleep pressure – is a need for sleep that keeps rising continuously from the time you wake up till when you go to bed. When you sleep, this pressure is alleviated.
The second of these processes – wake drive – also builds from morning to night, and effectively counteracts the rising sleep pressure to keep you alert and functional during the day.
The timing of these internal rhythms can shift in response to external signals. In this article, we’ll discuss how this works and what you can do about it.
To set the timing of your wake rhythm, your brain wants to coordinate the timing of your wake signal to daytime. It does this primarily by measuring the intensity and hue of light entering the eye. Exposure to bright light – like from sunlight – anchors your wake rhythm. We evolved to respond to this signal.
Exposure to bright light – like from sunlight – anchors your wake rhythm.
Herein lies the problem. Indoor light is far less intense than outdoor light, and we spend more of the day indoors than ever before in human history.
This effect is compounded by getting too much artificial light at night through electronic devices. Essentially, by having light enter the eye at night when the brain should be getting exposure to darkness, we are again telling the brain that it should shift the timing of the wake rhythm forward.
Consequently, living in the modern world causes a double-whammy – too little light during the day and too much light at night. This shifts your wake rhythm forward, and produces a mismatch between your internal timing and the timing of the environment. This results in what we refer to as circadian misalignment, and we’re only just now starting to fully appreciate the implications of this for health and daily function.
Let’s say you need to get up at 7am and want to go to bed by 11pm. Remember, you start to build sleep pressure as soon as you wake up. This isn’t a problem if your wake rhythm starts at 7am too. Everything works really well when these systems are coordinated.
But, if your wake rhythm is shifted forward, let’s say to 9am, you experience morning circadian misalignment. You’re making yourself stay awake, eat, work, etc. when your internal clock is still promoting sleep. There is a gap between the intensity of the two counteracting forces of sleep pressure and wake drive, and that gap is maintained all day.
What do you experience when this happens? You probably know the feeling: Day-long sleepiness and impaired alertness (and a host of other cognitive issues). But it doesn’t end there.
Let’s look at what happens to sleep at night. In this scenario, you want to go to sleep at 11pm, and you’ve been sleepy all day, but since your wake rhythm is shifted forward, it’s at its most powerful at the time you want to go to bed. This can cause insomnia, or it can make the first phase of sleep shallower. Incidentally, the first phase of sleep should be the deepest, and this depth of sleep corresponds with the fastest reduction of sleep pressure. If you don’t wear down sleep pressure efficiently, you have to sleep longer to do so. But if you don’t sleep longer, instead waking by an alarm as most people do, you wake the next day with “sleep debt.” This means that you carry some of yesterday’s unresolved sleep pressure with you into tomorrow.
A mistimed wake rhythm can shorten your sleep by making it harder to go to bed at night, or it can disrupt the depth of your sleep, either of which can cause sleep debt.
So, a mistimed wake rhythm can shorten your sleep by making it harder to go to bed at night, or it can disrupt the depth of your sleep, either of which can cause sleep debt. What this means is that seven hours of sleep will feel more like six the next day. Conversely, you could get nine hours of sleep (which might be a lot for you) and still not feel well rested.
You can see why it’s difficult to directly answer the question, “How much sleep do I need?”
Sleep quality is not entirely dependent upon sleep duration. Sleep quality could be disrupted by a wake rhythm that is overly active in the first part of the night. This could make it hard to nod off, or make the first (and deepest) sleep phase shallower.
The big lesson you should learn here is to anchor your wake rhythm by maintaining smart light habits throughout the day, evening, and night.
Here are three things you can do for good circadian alignment:
In the final article in this series, we will discuss how you can determine your ideal sleep duration – based on your individual needs and patterns – and what you can do to ensure you get that amount of sleep. Stay tuned!
Dan Pardi is an entrepreneur and researcher whose life’s work is centered on how to facilitate healthy behaviors in others. He does research with the Psychiatry and Behavioral Sciences Department at Stanford, as well as the Departments of Neurology and Endocrinology at Leiden University in the Netherlands. His current research looks at how sleep influences decision-making.
He is also the CEO of humanOS.me (formerly known as Dan’s Plan), a health technology company that utilizes the Loop Model to Sustain Health Behaviors – which he developed – to help people live a healthy lifestyle in a modern world.
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