Episode 192: In today's solo episode, I dive into the science behind sleep. Why do we do it? How much should we be getting? What's a sleep chronotype and why should you know yours? How does circadian rhythm work? Is our sleep quality good enough? This podcast answers all these questions and more.
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Chris Sandel: Welcome to Episode 192 of Real Health Radio. You can find the links talked about as part of this episode at the show notes, which is seven-health.com/192.
Seven Health is currently taking on new clients, and there are a handful of reasons that clients commonly come and see us. Hypothalamic amenorrhea is probably the first one, and this is the fancy name for not getting a period. This is often the result of undereating and over-exercising for what the body needs, irrespective of your actual size, and it’s almost always coupled with body dissatisfaction and a fear of gaining weight.
We work with clients along the disordered eating and eating disorder spectrum. Sometimes clients wouldn’t think to use the term disordered eating to describe themselves, but they notice that they’re overly restrictive with their eating, they fear certain foods, whether that be bread or carbs or fat or processed foods, they feel compelled to exercise excessively, and/or they find themselves binging or feeling out of control around food.
There are clients then who want to move on from dieting. They’ve had years or decades of doing so and realizing that it’s just not working, but they’re struggling to figure out how to do food without dieting. What should they eat? How do they listen to their body? What will happen with their weight? They’re confused and overwhelmed and just don’t know where to start.
Then the final one is body dissatisfaction and negative body image. For many clients, they experience feelings of body shame and hatred, and they find themselves fixated on weight and determined to be a particular size and frustrated with what they see in the mirror. They may even avoid social events or opt out of photographs or put off appointments with doctors as a result of negative body thoughts.
In all of these areas, we’re able to help, and do so through a mix of understanding physiology and psychology, so understanding how the body works and how to support the physical body, but also being compassionate and uncovering the whys behind clients’ behavior and figuring out ways that they can change this.
If any of these are areas you want help with, then please get in contact. You can head over to seven-health.com/help, and there you can read about how we work with clients and apply for a free initial chat. The address, again, is seven-health.com/help, and it will also be included in the show notes.
Hey, everyone. Welcome back to another episode of Real Health Radio. I’m your host, Chris Sandel. This week I am back with a solo episode. It’s been a while since one of these has come out. I know I did a recent solo episode on coronavirus, but I’m talking more about the longer form solo episodes.
This is actually going to be a two-parter. It’s not a completely new episode, but it is one of my second editions where I do a rewrite or a re-update of a previous episode that I’ve done, and this one is all about sleep. The first edition of this episode was Episode 17 and came out in November 2015, so roughly 4-½ years ago.
But before I go any further, let me start with the book giveaway. We are now giving away a book from our Resources page with every episode, and the winner for this week is Dylan R. Dylan, thank you for the review. We’ll be in contact and sending you a book of your choosing.
Reviews help increase the visibility of the podcast, and they enable us to reach and help more people. They also give you a chance to win a book. All you need to do is leave a review on iTunes, take a screenshot of it, and then email it to info@seven-health.com, and then you’ll permanently be entered into the drawing. Back to the episode now.
This has been an episode I’ve wanted to update for a long while now. I’ve been such a huge proponent of the importance of sleep, and it’s something I’m always working on with clients. In the last 4 years, there’s been so much new information that I’ve learnt that I want to be including in the second edition.
There are a handful of sources that have had the biggest impact on me in terms of this new information. Most recently and most profoundly, it is Matthew Walker’s book, Why We Sleep. I know I’ve mentioned it a number of times on the podcast before, I think with Alan Flanagan and Elyse Resch and there’s been other guests where I’ve referenced it. It was also one of my favorite books from 2019, so it was in that episode where I cover all my favorite things at the end of the year.
It was actually a book I’d been seeing for an umber of years whenever I’d go near a WHSmith or I’d be in an airport or whatever. It seemed to always be outward-facing. I’d see it and I just kept passing it by. I finally got around to ordering it and reading it, and I’m really glad that I did.
The other source that influenced my understanding around sleep is Ari Whitten and his Energy Blueprint Program. I’ve had Ari on the podcast a number of times in the early days of the show, and I have a lot of respect for Ari – although I would say over the years, our ideas have diverged and we’re serving very different segments of the health space. But while we have plenty of areas of disagreement, I still continue to follow his work to see what he’s up to and what he’s focusing on.
The Energy Blueprint is Ari’s flagship program, and it has a whole section on sleep. When I first watched this – it would’ve been a number of years ago – there was a ton that I learned from it, and a lot of what I subsequently read in Walker’s Why We Sleep book were ideas that I’d first heard Ari talk about.
So those are probably the two biggest sources. There’s also been some papers that I’m going to make reference to and we’ll also link to in the show notes.
With previous episodes where I’ve done the second editions, it’s been more of an update where the structure has stayed the same and I’m simply adding in new sections. This is more like a complete rewrite. Some of it has stayed the same, but rather than telling you, as I have in other second editions, what’s new information, just assume that it is all new.
This was going to be a single episode when I started working on it, but it just became apparent that this was going to be way too long for a single episode. I think it’s one thing to have a conversation that is 2 hours or nearing 2 hours; it’s another with me to be simply talking for that length of time where it can be quite dense information.
In this Part 1, I’m going to be looking at the mechanics around sleep, what drives us to sleep. We’ll look at circadian rhythm. I cover chronotypes and explain what this is and how it changes through various life stages. I’ll cover sleep health and how we define the term, and then finally look at what happens during sleep, so covering sleep cycles, REM versus non-REM sleep, and then the functions of sleep. So that’s what we’re going to cover in this one today, in Part 1.
In Part 2, it’s going to be all the recommendations based on this information. So if you want to maximize the benefit of sleep, what can you be doing?
What I also want to do with that episode is highlight things that are especially relevant with the clients that I see, because context matters, and while there’s lots of ideas and suggestions that were made in say Why We Sleep, this book is aimed at the general audience, talking to everyone in the population. The vast majority of the clients that we’re working with here are suffering with disordered eating and eating disorders or chronic dieting, and this is often coupled with over-exercise.
I want to make sure that I frame Part 2 to take this into account because if you have an eating disorder, for example, your reasons for poor sleep can be very different from the general population. There will obviously be some overlap and things that are universal, but other issues are going to be more specific, and I want to make sure that I address this.
Both with Part 1 and Part 2, I don’t want to fall into the trap of healthism around sleep. To quote Lucy Aphramore in terms of healthism, it is “the belief system that sees health as the property and responsibility of the individual and ranks the personal pursuit of health above everything else. It ignores the impact of poverty, oppression, war, violence, luck, historical atrocities, abuse, and the environment, which includes traffic, pollution, clean water, etc. It protects the status quo, leads to victim blaming and privilege, increases health inequalities, and fosters internalized oppression. It judges people’s worth according to their health.”
Someone’s ability or lack thereof to get proper sleep is not completely within their control. Shift work may be associated with negative health consequences, but often people don’t have a choice around this, and this is maybe the work that they need to do to put food on the table. Or they choose to do this work because they think it is valuable work, but by the nature of that job, they have to work nightshift.
Health isn’t the only consideration when someone makes choices, and very often it is less about a choice and more about what has to be done. So everything I say in these two podcasts is looking at the state of what we know with science; it’s not a moral imperative that you have to follow it. This is especially true when I get to Part 2 of the podcast and we’re addressing things that can be done to support proper sleep.
See these simply as potential options. Some won’t be options at all – no matter how much you’d like them to be, they simply aren’t on offer to you – and others will be options, and if you choose to, you can implement them. So that is an overview of these next two podcasts.
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To begin with, what I want to do is start by looking at our drive for sleep and the two systems that we have in our body that push us towards sleeping, and hopefully this means sleeping in a rhythmical and regular fashion.
The first system is described as sleep pressure or sleep/wake homeostasis. Homeostasis is the desire to find equilibrium to create a stable internal state. Our body is trying to get the balance right between us being awake and us sleeping, as both of these are important for our health and for our survival.
If you are getting adequate sleep, when you wake up in the morning, you feel refreshed. As the day goes on and you’ve had a longer and longer time of being awake, your body starts to feel tired. A big reason for this tiredness or sleep pressure is a substance called adenosine. Adenosine is a chemical substance that’s produced in the body, and the longer time we spend awake, the more adenosine is built up. Adenosine has receptors in the brain, and as more of it hits the receptors, the more tired you get. As the levels rise higher and higher, the more we have the desire and drive to find sleep.
When we finally do sleep, part of the process that then occurs is the clearing and the breaking down of adenosine. As sleep goes on, you have less and less of it, and by morning time, if things are as they should be, enough of the adenosine has been cleared so that when you wake up, you feel refreshed and then you start that whole process again from day to night.
So sleep pressure, or that tiredness feeling that we get after being awake for an increasing amount of time, is partly down to adenosine buildup.
Two things I should mention here. One is to do with caffeine. The way that caffeine works and why it helps people to feel less tired is it fights for the same receptor as the adenosine and it replaces it, or it prevents the adenosine from locking onto the receptor. This means that the adenosine is still continuing to build up in the background; you’re just not noticing the physiological effects because of the caffeine. That continues on until the caffeine is then broken down, and then you really notice how tired you are, which can then be experienced as a caffeine crash.
The second thing is to do with sleep debt. Just like with credit cards, you can get into debt, you can get into debt with sleep, meaning you have slept less than you need, and this lack of sleep is accruing just like a credit card. Adenosine is a big part of the reason for sleep debt.
Now, as I’m going to talk about when we get on to the functions of sleep, there’s a lot going on while we sleep. A big part of the debt is also to do with repair that is being missed out on. But in terms of the feeling of being sleep-deprived or still feeling unrefreshed after a good night’s sleep or many good nights’ sleep, it is partly because of adenosine. Because of the sleep debt, the body’s not able to clear it as it should overnight, so when you wake up, there’s still high enough amounts on the receptors that is then sending the message to your body to say you are still feeling tired.
This can be cleared with enough time and enough sleep so you get back to feeling refreshed on waking, but it takes time.
Let me just quote Walker on the topic of sleep debt: “The recycle rate of human beings is 16 hours. After 16 hours of being awake, the brain begins to fail. Humans need more than 7 hours a night to maintain cognitive function. After 10 days of just 7 hours’ sleep, the brain is as dysfunctional as it would be after going without sleep for 24 hours. Three full nights of recovery sleep, i.e. more nights than a weekend, are insufficient to restore the performance back to normal levels after a week of short sleeping.”
So adenosine and sleep pressure are the first components of the drive towards sleep.
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The second component is circadian rhythm. Most people have heard the term circadian rhythm and know it as maybe the body clock or the patterns that occur across a day. At different points of the day, different functions are going on, and these follow a daily structure. This is obviously with things like say the wake and sleep cycles, but it also impacts on different organs and different body systems where they’re doing different things at different points of the day.
How does circadian rhythm work? In the brain, you have an area called the suprachiasmatic nucleus, or SCN. It is a tiny region of the brain in the hypothalamus, and it is basically your master clock. It is guiding your body. Scientists have actually found other circadian clocks around the body. There is an article that I’m going to link to in the show notes where they found clocks in the liver and in the skin. But really, there are clocks in all tissues in our organs and are a way for our organs and our systems to know what time it is and therefore what they should be doing.
In my original first edition of this podcast, I talked about circadian rhythm being impacted upon by light and dark cycles. As humans, we’ve typically been awake during the daytime and asleep at nighttime, and this is down to the impact of light and circadian rhythm – which is true. In this first episode, I gave the examples of cortisol and melatonin to show what happens across a 24-hour cycle because of how these hormones are connected to sleep and wake.
As the sun rises, the light stimulates the body to produce cortisol, which is released from your adrenal glands, and while cortisol is normally talked about as a stress hormone, it actually has lots of functions in the body. In this instance, it can be thought about as an activating hormone, and it prepares the body for movement and work and other activity. As the body’s physiological systems developed a long time before fire and artificial light, the body works on the equation that light = sunshine and then releases cortisol for daytime activities.
Cortisol levels start to rise from sunrise and then for the next 2 or 3 hours, peaking at around 8:00 or 9:00 a.m., and levels then drop slowly but remain decent enough until around midday, and then as the afternoon wears on, cortisol drops more significantly, especially as the sun goes down.
As cortisol levels fall, your pineal gland begins to release melatonin. Melatonin is commonly known as the sleep hormone. It is released as light decreases, and this can explain why you may start to get tired in the middle of the winter at 4 p.m. if it’s dark outside. I like Walker’s analogy of melatonin. He says melatonin is like the starting gun of a running race. It gets everyone to the start line, but it doesn’t participate in the race. But through the secretions of melatonin, it helps other processes that then allow you to sleep.
Secretion of melatonin continues to rise into the middle of the night and then gradually starts to fall until morning time, and then once again, cortisol starts rising up, helping to pull you out of sleep to start the day, and that whole process starts again.
Cortisol and melatonin are two hormones that follow a circadian pattern each day and impact on our desire and our drive to be either awake or to be sleeping.
In the original episode, I really focused on how dependent the circadian rhythm is on the light/dark cycles, which is kind of true, but is not completely true. This was actually one of the most fascinating experiments that Walker talked about in the book.
It was done in 1938 by two scientists, and they wanted to see what would happen to circadian rhythm if they were in complete darkness. They lowered themselves into a cave that was so deep that there was no detectable light that could reach them. They lowered down beds and food and measuring devices with them, and then they started in complete darkness for 32 days.
What happened? Despite the complete lack of light, they followed a fairly predictable pattern where they would be awake for roughly 15 hours, followed by roughly 9 hours of sleep. So even without light, the body is still able to keep a circadian rhythm.
But interestingly, without the presence of light, rather than keeping to a 24-hour rhythm, it was actually longer. Between 26 and 28 hours for one of the men, and then a bit over 24 hours for one of the others – which is actually where the name “circadian rhythm” comes from. It’s a combination of two Latin words, where circa means approximately and dia means daily, so approximately a day.
If our bodies were consistently following a circadian pattern of 26 or 28 hours, things would get pretty messy. You’d no longer be following the 24 hours that it takes for the sun and the moon and would get into periods of sleeping all day and being awake all night. This is where, then, the influence of light impacts on the circadian rhythm – and not just light, but many other factors. Eating and movement and temperature and a whole host of factors can impact on circadian rhythm.
These factors are called zeitgebers, which comes from the German that means synchronizer or time-giver. It’s these other factors that then help to reset or reinforce what time of day it is. So rather than your body working on a 26-hour cycle that it would be if it was in total darkness, it then keeps to a 24-hour cycle.
It’s these two systems, the sleep pressure and the adenosine and then the circadian rhythm, that are what help us and drive us toward being awake or being sleep.
One thing that Walker points out is that these systems, while often in sync, are actually completely separate to one another. They’re not interconnected at all. They don’t talk to one another.
A good example of this is if you pull an all-nighter. Let’s say you’re studying for an exam and you stay up all night studying for the exam, and let’s imagine that you manage to do this feat without the aid of caffeine. Typically at say 3 a.m. or 4 a.m., it’s going to be super difficult to stay awake. You’re going to be feeling tired because of the high amounts of adenosine and also because your circadian rhythm is telling you this is when you’re normally asleep.
But then if you make it to 10 a.m., now you may start feeling less tired than where you were at 4 a.m. If you were to actually take a nap at 10 a.m., it’s unlikely you’re going to sleep for the usual 8 hours, and this is because while you have high amounts of adenosine creating the sleep pressure, your circadian rhythm is telling you it’s daytime; you should be awake now – which is also why jet lag is a thing. While you may have high amounts of sleep pressure from being awake for a really long time, it could be bedtime in your new location, but your body clock is still on the time of the previous destination and thinks it’s daytime.
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What I want to also add as part of this idea around circadian rhythm is a lot of this is genetic. Because of the genetics, there are those that have preferences for when they want to be going to bed – preferences for going to bed earlier and waking up earlier or going to bed later and waking up later. You’ve probably heard the expression of morning types or night types, or larks and owls.
This is fairly genetically predisposed, and the name for whether you are an early-to-bed person or a late-to-bed person is known as a chronotype. There’s actually a sleep specialist called Dr. Michael Breus who’s done a fair bit of work on chronotypes, and rather than just two chronotypes, he breaks people into four different chronotypes, which he details in his book, The Power of When – which I have to admit I have not read, but I’ve heard him on podcasts before, and he talks about there being four different chronotypes that he categorizes as animals: dolphins, lions, bears, and wolves.
What he talks about is that not only does your chronotype impact on your sleep preferences, it also then impacts on what time of day you’re going to be most wakeful, when you’re going to be best at doing deep work, when you’re going to be best at exercising, etc. He has a quiz that you can take, which is thepowerofwhenquiz.com, and you answer some questions and then he emails you to say which chronotype you are, and I imagine if you buy his book, the quiz and answers are in there.
As I said, I haven’t read the book. From what I’ve heard and seen online, I like some of his ideas but not all of them. Some of it feels pretty diet-y, and a lot of it feels a little bit like horoscopes, so it’s not perfect, from my perspective.
But when I did the test a handful of years ago and then got to read the results, it did seem to describe what I had already figured out about myself through self-awareness – things like I much prefer going to bed early and waking early; I’m much more productive in the morning for certain tasks like writing; if I’m going to do exercise, morning is my better time; breakfast is my favorite meal, and I wake up hungry. So for me, the test didn’t actually lead to any changes because of the advice; it more supported what I already knew about myself.
There is another online test that you can do, and this one is by the site Sleep Habits. I will link to it in the show notes. With these tests – and there’s multiple ones you can do online – there is a degree of habit that can get in the way of these results. What I mean by this is this normally trends in one direction: people think that they should be going to bed later than actually is ideal for them. There are many people who feel that they are night owls or later-to-bed people, but actually, this is a habit rather than a genetic predisposition. This is an entrenched habit that can then skew how questions are answered.
I would say that this normally trends in one direction because I think it is rare that someone is truly a night owl and someone who has a genetic predisposition to going to bed later, but is taking themselves to bed at 9 p.m. It’s much more likely that someone is genetically predisposed to be an early bird or someone who needs to go to bed earlier, but yet they’ve gotten into a routine of going to bed later.
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I should also note that circadian rhythm changes as we go through life stages. For example, infants and young children have a naturally much earlier circadian rhythm. They go to bed earlier and they wake up earlier – and I’m not talking about newborns here, but more at the point once a child is having one long sleep throughout the night and maybe a nap during the day.
Yes, in total, they’re going to be sleeping a lot longer hours than adults, but even when this is taken into account, they go to bed earlier and wake up earlier – going to sleep say somewhere between 6:30 and 8 p.m. and then waking somewhere between 5 a.m. and 6:00 or 6:30 a.m.
Then as kids get older, but before hitting adolescence – someone who’s 8, 9, 10, 11, that kind of thing – their sleeping becomes more like an adult whose preference is for being a morning person. But they’re still needing more sleep than an adult. Their total sleep time decreases from when they were younger, but it also shifts so that they’re going to bed a little later and waking a little later, maybe going to bed at 8:30 or 9 p.m. and waking at 6 or 7 a.m.
But then in the teenage years, and especially the late teenage years, this is where things drastically change. Circadian rhythm shifts to being much later, so going to bed later and waking up later. In Walker’s book, he offers the potential evolutionary explanation for this as that this is coinciding with a time in a teenager or an adolescent’s life where there’s greater individuation, so teenagers are then up later than the adults.
I actually remember this from my teenage days. I mentioned earlier that I’m definitely an early-to-bed and early-to-rise person, and for my teenage years I did mostly keep this up, but that was probably because I was having to get up at 5:30 a.m. to get to school on time. But I do remember in the holidays in my final year of school, when I was studying for my final exams, my best studying would be done between about 10 p.m. and 2 a.m. This is when I was most focused, this is when I was most productive.
I would then go to bed after that and probably wake up around 10 a.m. or 10:30 a.m. This had never been my pattern before, but because of the changes that were happening as part of adolescence and changes that then occur because of the circadian rhythm, I became a night person.
This makes school starting times for teenagers a real issue. Interestingly, some statistics around this – a century ago, schools in the U.S. started at 9 a.m., and now 80% of schools in the U.S. start before 8:15 a.m. and 50% start before 7:20 a.m. What this typically means is that teenagers are getting much less sleep then they ideally should, and also waking up much earlier than they ideally should. This means that they’re missing out on a lot of sleep and a lot of REM sleep, which I will touch on in a little while.
They’ve actually done pilot studies around this where they started school time later, and this was the only thing that they changed, and this alone created higher test scores.
I think the same way about adults as well who are truly night owls. The world of work is changing, but it is still largely set up for those who go to bed early and wake up early. So if your chronotype isn’t set this way, the inadvertent consequences of having to get up earlier than ideally your body would like to are really huge. There’s a connection between mental health issues with many of these, beginning in teenage years and having to get up earlier, and while insufficient sleep may not be the only cause or the primary cause, it makes it much more likely or more severe.
Starting school later also leads to less fatalities by fewer car accidents. I think this is applicable to teenagers who are new to driving, but is also applicable for all drivers. One of the most eye-opening parts of the book is the statistics around sleep and our driving ability.
This can be viewed from two angles. The first is how long you’ve been awake for. Once you’ve been awake for more than 15 hours, your ability to operate a car nosedives, which means if you woke up at 6 a.m., by 9 p.m. it’s become much more dangerous for you to be behind the wheel. By 19 hours of being awake – so if you woke up at 6 a.m., by 11 p.m. – you are as cognitively impaired as someone who is legally drunk.
The other angle that you can explore this from is looking at limited sleep and how, if you’ve had limited sleep and then drive, this impacts on things. If you’ve had between 5 and 6 hours’ sleep, you’re nearly double as likely to have a crash. If you’ve had between 4 and 5 hours’ sleep, you are over four times as likely to have a crash. And if you get under 4 hours’ sleep and then drive, you are 11 times more likely to have a crash.
If you’ve had less than 4 hours’ sleep or you’ve had 8 hours’ sleep but are legally drunk, your chances of having a car accident are the same. I read those statistics and I think of all new parents driving out of the hospital with their new child, and they’re probably the equivalent of being legally drunk at a time when they have this new, precious human in the car and they just want to protect it.
If you combine having less than 4 hours’ sleep and also being legally drunk, then the chance of an accident is 30 times more likely. Drunk driving when combined with lack of sleep is way more of a problem than simply drunk driving on its own. For me, bring on driverless cars.
But let’s get back to the circadian rhythm changes throughout life. I mentioned that as a teenager, I was most productive between 10 p.m. and 2 a.m., and I had this spell where that was going on. I know if I tried to do that now, I would find it impossible, but this just happened because of the developmental state that I was in.
I’m not sure at what point this then regressed to a more reasonable time. I know by 21, when I moved to the UK, I was definitely more of an early-to-bed type during the week – and yes, if I was going out, I would stay up later on weekends and would deprive myself of much-needed sleep, but during the week I would be taking myself to bed before or by 10 p.m. each night, and on weekends, if I wasn’t out, my weekends were the same as my weekdays.
This is what then happens in adulthood, where we settle into a circadian rhythm and then you have that chronotype for your adult life. That’s then until you hit older age, and in older age you have a tendency again for circadian rhythm to become earlier, so you’re going to bed earlier and you’re rising earlier.
So that is the circadian rhythm throughout different life stages. But if there is anything that I want you to take from this section, it’s that we all have a chronotype that we are genetically predisposed to and that this dictates, in an ideal world, when we should be doing our sleeping.
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Before I jump into the actual process of sleep and what’s going on, I want to define sleep health. How do we know if we’re getting enough sleep or if the quality of our sleep is good enough?
This isn’t actually so easy to subjectively know. When we are sleep deprived, we never notice how much of an impairment this is causing. I bet you’ve driven home after being awake for 19 hours and didn’t feel like you were legally drunk.
Our subjective ability to rate how much we are sleep deprived or if we’re getting enough sleep isn’t the greatest. Obviously, you can go and do a sleep study where they can look at how much sleep you get across a night and you’re wired up, so they look at your brainwave activity, they can see how much time you’re spending in the different stages of sleep and compare this to what is recommended – but even with this, it’s not answering the question around sleep debt, as it’s just looking at that night.
The other issues with this is that people can sleep worse if they’re in a room that they’re not used to being in and if they’re hooked up to machines. I know that there are now sleep studies that you can do at home where they give you a device that you set up to monitor all this, but the reality is, for most people, they’re just not going to do this unless they think there is something untoward that needs to be looked at.
This means that we’re typically reliant on various signs and symptoms to estimate what sleep quality is like and to determine how well we’re doing from a sleep health perspective.
In Walker’s book, he talks about two easy indicators that tell you you’re not getting enough sleep. There can be much more subtle signs of sleep debt or poor sleep, but if either of these two are happening, it’s a fairly clear sign.
The two questions are: after waking in the morning, could you fall asleep again at 10 a.m. or 11 a.m.? The other question is if you can’t function optimally without caffeine before noon. If you answer “yes” to either of those questions, then you are not getting enough sleep.
There’s also a paper that addresses sleep health in much more detail. It’s called “Sleep Health: Can We Define It? Does It Matter?” I’ve linked to it in the show notes. What I want to do is use the definition of sleep health from this paper.
They define it as a “multidimensional pattern of sleep/wakefulness adapted to individual, social, and environmental demands that promote physical and mental wellbeing. Good sleep health is characterized by subjective satisfaction, appropriate timing, adequate duration, high efficiency, and sustained alertness during waking hours.”
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As part of this definition around sleep health, they point to 5 dimensions that appear relevant when we’re looking at this to try and define and measure it, especially if we’re trying to do that at a population level.
Dimension 1 is sleep duration. This is the total amount of sleep obtained per 24 hours. While people will differ in their needs, Walker typically advises to get a minimum of 8 hours’ sleep. In the question as part of this paper for duration of sleep, they asked: are you getting between 6 and 8 hours a night? But I’d say based on the book, this is probably lower than should be recommended.
As a side note, there’s also a difference between actual sleep time and sleep potential. For example, if you go to bed at 11 p.m. and you have to be up at 7 a.m., you’ve given yourself a maximum sleep opportunity of 8 hours. But if it takes you 20 minutes to fall asleep after getting into bed, then your actual sleep time is 7 hours, 40 minutes. When figuring out sleep duration, this needs to be taken into consideration, and if you actually need 8 hours of sleeping time, you need to give yourself a sleep opportunity that is longer than this because of the time it takes to fall asleep and/or the time that you will then awake in the night if this happens.
Back to the 5 dimensions. Number two is sleep continuity or efficiency, which is the ease of falling asleep and returning to sleep. The question with the paper for this one is: do you spend less than 30 minutes awake in the night? This includes the time to fall asleep and the awakening from sleep.
It takes a while for the mind to shift into sleep mode. Anywhere from 10 to 20 minutes is a normal amount of time to be awake and then going to sleep. Any less than about 10 minutes could be an indication you’re in need of going to bed earlier or you’re sleep deprived. Any longer than 30 minutes and it could point towards something else, and I’ll deal with some of these when we look at the sleep recommendations and some of the things that could be getting in the way of someone falling asleep easier.
It’s also worth noting that it is completely normal to wake for brief moments throughout the night. As I’m going to talk about in a little while, throughout the night we go through sleep cycles, and between some of these cycles, it’s common to wake up briefly before going back to sleep. So just because you remember waking a handful of times in the night, doesn’t mean there’s an issue or you’re sleeping badly. If these are brief moments of awake time and it’s easy getting back to sleep, then this is completely normal as part of good quality sleep.
Dimension 3 is timing. The placement of sleep between or within the 24-hour day. As I talked about earlier, our body has a circadian rhythm that we’re meant to follow, and some of this is dictated by our genetics, but it’s also impacted upon by the zeitgebers like light and dark and food intake and movement and social interactions and other factors that nudge and tell the body what time it is.
The question asked for this one in the paper is: are you asleep or trying to sleep between 2 a.m. and 4 a.m.? The reason for asking about this specific time is regardless of whether you are genetically wired to be an early-to-bed person or a late-to-bed person, biologically, between 2 a.m. and 4 a.m., we should all be sleeping.
During Part 2 of this podcast, I’m going to make some recommendations with sleep timing, so we’ll come back to this one later on. But suffice to say that there are better metrics than simply looking at if someone’s asleep or attempting to be asleep between 2 and 4 a.m. to look at sleep timing.
Dimension 4 is alertness and sleepiness. This is the ability to maintain attentive wakefulness. The question in the paper for this one is: do you stay awake all day without dozing? Now, obviously there are cultures where they have a siesta or a nap during the day, and this is fine. There’s actually some solid evidence that Walker talks about in his book about the benefits of this kind of a routine. This question is more talking about dozing throughout the daytime when the intention isn’t to be having a nap and where a nap isn’t part of your routine.
Then the final dimension, the fifth dimension, is satisfaction or quality. This is a subjective assessment of good or poor sleep. All the questions up to this point had been quantifiable; they were yes/no questions based on whether you were inside or outside of some parameter. But this final question is subjective, as it asks: are you satisfied with your sleep?
Those are the 5 categories that this paper looked at in terms of sleep health, with the suggestion that when we’re trying to address sleep as a health indicator at a society level, that we focus on these metrics as a way of determining how we are doing.
Obviously, at an individual level, there are many questions that could be asked and there are many indicators that could be looked at, but based on metrics for population-wide sleep health scores, this is the starting place that this paper is recommending.
The paper did mention a potential sixth idea, which is sleep adaptability, which is defined as the ability to sleep well under conditions of physical, psychosocial, or chronobiological stress – which is something to consider, because it is one thing to sleep well when life is going perfectly and everything is lining up with your sleep hygiene routine, but it’s another, if this doesn’t happen, that it completely knocks you out of place and you can’t sleep under these kind of conditions.
The problem with this as a potential parameter or dimension is the difficulty in how you quantify this. Again, this would be subjective, so they’re unsure about how to even start to measure this. So it was a footnote rather than a sixth factor.
That is that paper and the idea of sleep health.
00:44:35
I now want to focus on what’s going on when you are sleeping. There are three sections here. There’s sleep cycles, then there’s the difference between REM and non-REM sleep, and then finally the repair and function of sleep. Let’s start with the sleep cycles.
Throughout the night, when sleeping, our body goes through five or six cycles, with each of the cycles lasting anywhere between 70 to 120 minutes. Walker talks in his book about cycles being roughly 90 minutes, but there is research to show that this time varies among humans, so some people can be longer, some people can be shorter. Also, cycle length varies depending on the stage of night. The first cycle at night can be different length to say your fourth cycle at night.
There is a great graph that I will link to in the show notes that visually makes this super easy to understand. It appears in an article called “The Science of Sleep: Stages and Cycles,” but given a podcast is an audio-only experience, let me explain it as best I can.
During each sleep cycle, you move through different brainwaves and sleep depth levels. There are two broad sleep categories: REM sleep and non-REM sleep, where REM stands for rapid eye movement, and it gets its name from the moving of the eyelids that occurs during this phase of sleep. REM sleep is considered one category, and then within the non-REM sleep category, there are four different stages, which are cleverly labeled Stage 1, Stage 2, Stage 3, and Stage 4. Each of these stages relates to the depth of sleep. Stage 1 and Stage 2 are lighter sleep, and then Stage 3 and Stage 4 are deeper sleep.
During each sleep cycle – which, as I said, lasts roughly 90 minutes – we move through these different stages. We start with REM; then we work through all the non-REM stages, starting at 1 and going all the way down to 4. Then we work back up, starting from Stage 4 and going all the way back up to Stage 1, and then back into REM sleep. That is one cycle, and then we do it all again.
But each cycle isn’t a carbon copy of the one previously. Typically, in the early part of the night, especially in the first two cycles, we are spending the vast majority of our time in non-REM sleep, and a lot of that is deep sleep, so in Stages 3 and 4. Then around the midpoint of the night, our non-REM sleep and REM sleep are about even in how much time you spend in it for that cycle. Then as the night goes on and further cycles happen, you’re more heavily weighted towards REM sleep, and when you’re in non-REM sleep, it’s more likely to be Stage 1 or Stage 2 rather than it being Stage 3 or Stage 4.
With that graph that I talked about, you can see all of this as part of it. As part of that graph as well, it includes brief times later in the night when going from one cycle to the next where you actually wake up – which is what I just mentioned earlier. Brief wake-ups a couple of times a night, especially in the second half of the night, are common and normal with healthy sleep. For someone, this could be so short an amount of time that they won’t even remember it while other people can wake up, they can roll over, are awake just long enough to know that it happened, and then they drop off back to sleep again.
These cycles and how long your sleep cycles are and how many sleep cycles you need can be connected to how much sleep in total we need – and not just when you are sleep deprived, or even outside of sleep deprivation, but how much you need on a regular night.
The length of your sleep cycle, whether that’s 70 minutes or 90 minutes, when you then add them together, will determine how much sleep you need. Same thing with how many cycles your body actually needs. Is it five cycles or is it six cycles? Just like your chronotype, these are going to have a strong genetic underpinning.
Using myself as an example, I would consider myself a fairly healthy individual, and even when I’m doing all the things that are right and supporting myself, I do best on about 9 hours’ sleep a night. This isn’t me trying to catch up on sleep; this is simply what my body needs. There could be someone else who is living in a very similar way and in a very similar state of health, and what they need is 7.5 hours or 8 hours. These differences are at least in part connected to sleep cycling and the number of cycles per night.
00:49:55
The next thing I want to look at is REM and non-REM sleep and some of the differences that are occurring. To start off with, let me just quote Walker from his book when he talks about this: “The wakeful state is about reception, which is experiencing and constantly learning the world around you. Non-REM sleep is about reflection, so storing and strengthening those raw ingredients of new facts and skills. REM sleep is about integration, so interconnecting these raw ingredients with each other, with all past experiences, and in doing so, building an ever more accurate model of how the world works, including innovative insights and problem-solving abilities.”
If we use a gardening analogy, non-REM sleep is about putting in plants and pulling out weeds, while REM sleep is about the tending to what is maintaining and remaining in the garden and making it grow as best as it can.
If you look at brainwave activity of someone in non-REM sleep, it’s very obvious that they are asleep, as it’s just so different to wakefulness brainwave activity. But with REM sleep, it’s actually very similar in terms of brainwave activity to being awake – the big change being that motor skills are switched off when you’re in REM sleep. Seconds before entering into REM sleep, you are paralyzed. You have no muscle tone. This is because during this type of sleep, you are dreaming, and to avoid actually acting out your dreams, your body is paralyzed. Those things are just confined to the mind.
Throughout life, the percentage of non-REM to REM sleep changes. As a newborn baby, they spend about 80% of their sleep time in REM sleep. By 4 months old, there’s a pretty even mix, so 50/50 split between the two. By 5 years old, it’s more like 70% non-REM sleep and 30% REM sleep. And then in late teens and adulthood, the non-REM sleep then ramps up further to about 80%.
This increase coincides with a huge amount of pruning that then goes on at this stage of life. You’ve learnt for the first 15 to 18 years of your life what the world is like based on your experiences, and then in your late teens and adulthood is when there’s this pruning and getting rid of superfluous stuff that is no longer needed.
This is kind of where it stays, with non-REM sleep accounting for about 75-80% of sleep time and REM sleep accounting for about 20-25% of sleep time. So if you’re getting 8 hours’ sleep a night as an adult, about 6 to 6.5 hours of that is non-REM sleep and about 1.5 to 2 hours of that is REM sleep.
But as we just saw a moment ago, when we get our non-REM versus REM sleep isn’t evenly distributed across the night. The early part of the night is much more heavily weighted with non-REM sleep, with the latter part of the night being more about REM sleep. This matters a lot, especially if you aren’t getting enough sleep. How this then affects you will connect in with the idea of chronotypes that we talked about earlier.
If you are someone who needs 8 hours’ sleep but yet you’re getting only 6 hours’ sleep, this isn’t going to evenly affect REM and non-REM sleep. If you get only 6 hours’ sleep and went to bed at the usual time, but you get up 2 hours early, this is going to more drastically affect REM sleep because that’s when the majority of REM sleep takes place.
If you get only 6 hours’ sleep and yet you went to bed later than you usually do and then got up at the normal time, then you’ll miss out on more of the non-REM sleep because this was meant to happen in the earlier part of the night, where on this occasion you were still awake.
This is why total sleep time is important, but it’s also important about when this is occurring, which ties back into my earlier comments about teenagers and having to get up so much earlier because of school than their chronotype would like them to. If you’re missing out on sleep because of this, it’s going to be the REM sleep that they’re losing, and considering that REM sleep is about creativity and making connections to understand the world and how it works and their place in the world, it’s a huge loss for them to be missing out on this important chunk of sleep.
00:54:50
I now want to look at sleep as a whole rather than separating out REM and non-REM sleep to look at the functions of sleep. How does sleep support our health?
The simplest way to generalize is sleep is all about repair. It is when you are most active in turning over cells of bone and muscle and organ and tissues and replacing them with new cells. Our bodies are constantly in a state of catabolism and anabolism, and sleep is one of the most important times for this to happen.
It is when your immune system is at its highest. If you’ve ever noticed that when you have a cold or the flu, symptoms get worse at night, this is your immune system increasing. It does a huge amount of work while you’re asleep.
As a side note, while most people don’t know it, you can actually die from a lack of sleep, and pretty quickly. In experiments with rats, if you totally sleep deprive a rat, it will die just as quickly as if it was from total food restriction. On average, it takes 15 days. The same is true with humans. Total sleep deprivation for an extended amount of time does result in death.
When they investigate why this is, the actual mechanism for death is septicemia, which is an infection caused by large amounts of bacteria entering the bloodstream, and in the case of extended sleep deprivation, because of the septicemia, it then leads to death. This is because the immune system is so suppressed because of that sleep deprivation.
The World Health Organization has classified nighttime shift work as probably carcinogenic to humans. Again, this is because of the work the immune system is doing when we are asleep, or should be happening when we’re asleep.
Sleep is also the body’s cleanup time. Throughout the day, during many normal, healthy functions, substances are created that are damaging for the body. But by sleeping, the body then sends in the metaphorical cleanup crew and the bin lorries to remove all of these substances.
For example, there is a connection between poor sleep and Alzheimer’s disease. In Alzheimer’s, there is a building up of a substance called beta-amyloid in the brain, and when sleep is happening in the right amount and the cleanup process is happening, it helps to then go in and remove these substances on a daily basis. But if sleep is not occurring as much as it should be or it’s disrupted, then this process isn’t happening.
There are many factors that go into developing Alzheimer’s disease and its prevention, so I’m by no means saying that it is as simple as getting more sleep. But there is a connection between these two, and many other conditions that arise because of the body’s ineffectiveness in being able to clear substances that it should be getting rid of at the end of each day.
Sleep affects our hunger signals and when we feel full as well as the types of food that we crave. It does this by affecting many different hormones, but let me just focus on two of them, leptin and ghrelin. Leptin is a very powerful and influential hormone produced by fat cells, and it acts on receptors in the brain where it then inhibits appetite. Basically, it is a hormone that tells the brain whether or not you’re hungry and then what the state of your fat stores are.
Ghrelin is then another hormone to do with hunger, and ghrelin is secreted and produced by the stomach and the pancreas, and it increases before meals and then decreases after meals. As such, higher levels of ghrelin increase food intake.
It’s been shown that those who are not getting adequate sleep are more likely to have decreased levels of leptin and increased levels of ghrelin, and what this means is that you’re naturally hungrier and can need more food to feel full.
There was a podcast that I listened to that I will link to in the show notes that talked about this, and it was interviewing the head of a sleep lab who was doing research around how our food preferences change when getting less sleep than we need. The research showed that people tended to serve themselves and subsequently eat larger portions. There was more of a craving for highly palatable food and calorie-dense food, and people’s preferences for sweetness increased. What they said was the right level of sweetness for them changed, and when they were more sleep deprived, they preferred those sweeter things.
Just to clarify here, in case this is all sounding diet-y, I’m anti-diet. I’m a huge proponent of intuitive eating. But it’s worth noting that by simply altering sleep, the amounts and the kinds of foods that you are driven towards can change.
The podcast that did talk about this is rather diet-y and was fatphobic, so if you do want to listen to it, please keep that in mind. But I did think it was interesting, the research that was looked at as part of that.
Sleep is also crucial for sexual health and fertility. Poor sleep decreases libido. I talked about how poor sleep decreases leptin levels; leptin is useful also for reproduction. It’s not just simply about hunger and fullness. In women, it can impair ovulation, and in men it can lead to decreased numbers and quality of sperm.
But it’s not just leptin. Sleep affects progesterone and estrogen and luteinizing hormone and follicle-stimulating hormone and testosterone and really all crucial hormones for reproduction.
Sleep affects how we experience pain. With less sleep, the more sensitive to pain we are.
I could go on. Basically, sleep is important for every system of the body, whether you are talking about cardiovascular health, blood sugar regulation, your nervous system, your ability to adequately respond to stress – all of these are aided by sleep.
01:01:25
It’s especially important for exercise and exercise recovery, and I’ve done a whole podcast on exercise that I recommend listening to if you haven’t already because I think as a society, we have some pretty warped views around exercise. But for exercise to truly enhance health, your body needs to adapt, and to adapt, it needs adequate food and it needs adequate rest. Without these two, exercise is simply a stress on the body.
When people talk about things like muscle memory and the ability to do a new sport or a new skill, this is also because of sleep. There is a whole section in Walker’s book about sleep and exercise, which is great, but let me just quote some of it.
“Obtain anything less than 8 hours of sleep at night, and especially less than 6 hours a night, and the following happens. Time to physical exhaustion drops by 10-30%, and aerobic output is significantly reduced.
“Similar impairments are observed in limb extension, force, and vertical jump height, together with decrease in cardiovascular, metabolic, and respiratory capabilities that hamper an underslept body, including faster rates of lactic acid buildup, reduction in blood oxygen saturation, and converse increase in blood carbon dioxide, due in part to the reduction in the amount of air that the lungs can expire. Even the ability of the body to cool itself during physical exertion through sweating, a critical part of peak performance, is impaired by sleep loss.”
All these changes lead to then a downturn in ability and the body’s ability to cope and adapt. The body is then just failing to adequately repair. This might take a while for someone to notice. I’ve written articles before about how it’s often when people are doing the things that are overtraining their body that they can be performing at their best, but at some point, this drops off, and this is when things noticeably go south.
There’s also a connection that sleep loss predicts injuries in athletes. While the research was looking at athletes, the same would be true for people who don’t train but don’t think of themselves as athletes. Some of this is probably due to the lack of repair that then makes bones more brittle and likely to fracture or tendons less resistant. But a big part is also the negative impact of sleep loss on coordination and motor skills, so you move in a way that makes injury more likely.
01:04:05
Up until this point, I’ve mostly been focusing on the repair of the physical body through sleep, but sleep is also incredibly important for the mind. It’s how you process the mental and emotional events of the day and you refresh your mind for the day ahead. It assists your brain in piecing together unrelated ideas and memories, in creating connections that increase creativity and enhance performance and learning and memory.
Sleep before learning refreshes our ability to make new memories; sleep after learning helps to then save those memories. Sleep helps with attention. It leads to emotional rationality, where the opposite of this is that lack of sleep leads to emotional irrationality. Sleep also helps us to forget painful memories or parasitic memories. To quote Walker, sleep is “the nocturnal soothing balm that removes emotional sharp edges.”
There’s research around PTSD and sleep. Sleep should typically be a time of low stress, where the brain takes painful memories and is able to then tag them and process them correctly so that when you wake up the next day, they are not so painful. This, with a very painful memory, can take time, but through the process of sleep, especially with REM sleep, it means that you’re able to get over that situation.
Someone suffering with PTSD has excessively high levels of noradrenaline, and this occurs at nighttime as well as in the daytime. Because of this high amount of noradrenaline, it blocks the sufferer from entering and maintaining proper REM sleep. So while they’re having nightmares and clearly dreaming, because of the adrenaline and the high emotions, the brain isn’t able to tag and process the memory correctly. The next night, it is the same intensity, and then the next night, and it just stays at this level, never being soothed and processed by sleep.
In an experiment, they gave patients suffering with PTSD a drug called Prazosin, which lowers noradrenaline, and with time the nightmares greatly reduced in frequencies and symptoms improved. This wasn’t a panacea on its own; it doesn’t resolve PTSD on its own, but it helped to put the body in a state that sleep could help and do some of its healing.
So sleep really is just crucial for all mental and cognitive function. As I’ve mentioned a number of times, when we’re sleep deprived, we just aren’t very good at estimating how much of an impairment is happening. We are terrible at estimating how tiredness affects our ability to drive, but it equally affects our decision-making and our mental function in all realms.
Sleep is most simply the best thing that you can be doing for all the repair of our systems and to be supporting healthy functioning.
That actually brings this episode to a close. I hope that you now have a better understanding of sleep and how it works and why it’s important. During the next episode, Part 2, I’m going to be going through various ideas to assist in creating good quality sleep and restorative sleep, and also talking about, for a lot of the clients that I see, the things that get in the way of making that restorative sleep happen. So that will be Part 2.
As I mentioned at the top of the show, we are currently taking on new clients. If you are struggling with disordered eating or eating disorders or chronic dieting or body image or any of the topics that we cover as part of the show, then please get in contact. You can go to seven-health.com/help.
I will be back next week with Part 2 of this podcast. Take care.
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