Speaker 3
Yeah, I mean, no smartphones, no TVs, nothing to keep you awake at night. Surely they had nine hours every night. But today we're looking at an analysis of 54 sleep studies conducted around the world. And it's found that people in smaller non-industrialized societies are actually getting less sleep than us today in the modern world. Yeah,
Speaker 1
I mean, maybe that is less surprising, I suppose, that if you're sleeping in a hunter-gatherer setting, then, you know, you can imagine there's going to be things that wake you up, but it still doesn't fit with people saying how awful their sleep is all the time and what we hear about, you know, smartphones at night and stuff like that and this sleep loss epidemic.
Speaker 3
Yeah, it seems to become a bit of an obsession for some people, doesn't it? I mean, it turns out that some of these studies that report a decrease in sleep in the last few decades, they're based on asking people how long they sleep for, which, as we know, is quite an unreliable measure. And even using this method, the results are mixed. So lots of studies find that there are no change or even there's been an increase in sleep duration. If we use some more reliable measures, such as using activity monitors or electrodes to monitor brain waves, those studies haven't found a decrease in sleep over the last few decades. So, for example, there was a 2016 review of 168 studies and that found no decline in sleep duration over the past 50 years. But it's important to know that all of these studies were done in industrialised countries. So that leaves open the question of whether people got a lot more sleep before these societies industrialised. And now that we've got lots of high-tech risk-based activity monitors, we can start to monitor sleep in non-industrialised societies and start to answer some of those questions. Okay,
Speaker 1
so looking at this data, it shows that among hunter-gatherers, they do have shorter sleep durations. So the San in southern Africa sleep for an average of 6.7 hours a night. The Hadza in Tanzania, we often write about the Hadza, they sleep for 6.2 hours a night. The Bayaka in the Congo for 5.9 hours. The shortest duration found so far is 5.5 hours a night. And that's the Himba community in Namibia and their nomadic livestock herders. Maybe they have to get up and check on their animals throughout the night.
Speaker 3
Yeah, it could be something to do with their lifestyles just being so radically different to ours. But we could flip this and think about it the other way, which is that if we've got higher sleep duration and better sleep efficiency in industrialized societies, it's because we are safe and secure when we go to bed at night. We know that nothing is going to disturb us until the next morning. No, no lions are going to prowl around,
Speaker 1
eat us or our livestock and or humans are going to raid our village hopefully not anyway yeah
Speaker 3
okay so back to this new study which we've said is an analysis of 54 sleep studies that were conducted around the world so thanks to this new work we can now directly compare sleeping habits in industrialized societies like the US, Australia and Sri Lanka with sleep in smaller non-industrialised communities. So that's indigenous peoples in the Amazon, for example, or Madagascar, or the Tanner Island in the Pacific. And the result of that work is it found that people in non-industrialised societies sleep for an average of 6.4 hours a night compared 7.1 hours in industrial societies.
Speaker 1
So 7.1 is kind of what the recommended, almost what the recommended amount is. That's pretty good.
Speaker 3
Yeah, it's pretty good going. And also people in non-industrialized societies were asleep for 74% of the time were in bed. But people in industrialized societies were asleep for 88% of the time they were in bed. So they're better at just getting into bed and falling asleep as soon as possible.
Speaker 1
OK, so their sleep efficiency is better, or our sleep efficiency is better in industrialised societies. So we're doing better than we might have thought. In
Speaker 3
some ways, yeah, we're spending more time in bed asleep. But there is a flip side, which is that we don't get the same cues to maintain our circadian rhythms, such as lower temperatures at night and bright light exposure during the day. So industrialised people scored more poorly on that measure of matching their daily rhythm to the externalities of nature. Right.
Speaker 1
And that might answer the riddle, because if we feel we get bad sleep and we report on these self-reported questionnaires about having bad sleep, it might be the less regular circadian rhythms we have might make us perceive our sleep to be poor. Exactly,
Speaker 3
that might be one of the answers to this, yeah. OK, so let's talk about sleep debt now, because whatever our perceptions and our circadian rhythm status, we will all sometimes go through periods of having to get by without much sleep. As the mother of a young child, I can absolutely testify to this. Kat Delange is here to help us get out of debt. Kat, you wrote a piece on this recently. Is this really
Speaker 2
a thing? What does it mean to be in sleep debt? So it is a thing. It's something that scientists use and it's quite straightforward. It's really just that you're not getting enough sleep. So it might be that you had one night where you, I recently had a long haul flight and I did not sleep all night. So that's like a whole night's sleep that I've accrued in my sleep debt. Or it might be that you're just kind of going to bed a bit late or waking up early in the morning and chipping away at that sleep. And
Speaker 3
is it pretty easy to tell if you're in sleep debt? I mean, Rowan, you look like you've
Speaker 2
been missing a few hours recently. That's my
Speaker 1
natural look. I had a great night's sleep last night.
Speaker 2
Yeah, you can. So like the sort of standard way of doing it is if you need an alarm clock to wake up in the morning, then you're probably in some sort of sleep debt. Oh, I definitely am then. If your friends and family are telling you that your behaviour's changed so maybe you're a bit more irritable than usual or you're kind of experiencing a you're not connecting with people very well basically you're struggling with your social connectivity that could be a sign that you're in sleep debt and I actually use an app to track my sleep debt but maybe we'll get onto that a little bit later.
Speaker 1
Yeah we'll talk about tech in a bit but that point about moodiness that apparently comes because the connection between the the decision-making part of your brain in the prefrontal cortex and the amygdala which is this lovely mysterious little bit which is controlled or is involved in our fear and emotions that connection between those two things breaks down. So that might be why we start getting this sort of irritable.
Speaker 2
Yeah, and we know that sleep is really important for regulating our emotions, especially REM sleep. So that sort of dream sleep helps us to process our emotions. So if we're not getting that, then maybe we're kind of struggling with our emotions. Yeah. So
Speaker 1
I've heard that sleep scientists talk about this deficit, the sleep pressure that builds up until you have to go to sleep. But what about the debt? And what about the damage that it does? Is it more than just moodiness? What's it all about? Yeah,
Speaker 2
definitely. So part of the problem is that actually we're not very good at understanding the effect of a lack of sleep on our health and on our own sort of brains and moods. So in one study, for instance, participants were randomly selected to get four hours, six hours, or eight hours of sleep per night for 14 days straight. And by the end of that, those who got six hours or less had this sort of cognitive deficit that was equivalent to missing two entire nights of sleep. So just sort of chipping away at your sleep by a couple of hours over two weeks was the equivalent to staying awake for two nights straight. So that's actually huge. But despite that, and they did feel worse, but after a certain point, they stopped seeing the negative impact. So they kind of thought they were okay when actually their cognitive abilities were carrying on declining after night after night wow so you can have a false sense of how well you're functioning on a very little sleep absolutely so the way i think about it is you know we all have the odd occasion where we stay up too late and maybe that is like the equivalent of splurging on an expensive dinner out with your friends. OK, so that's taking a dent on your bank balance, but it's a bit of a one off. Right. On the flip side, there's sort of regularly going night after night with not enough sleep. And you might think at the time, well, I got, you know, I got six and a half hours last night. It's not too bad. But if you're repeatedly doing that, you're building up this debt. This is a problem for a lot of people. So the Centers for Disease Control in the US reported that a third of adults get less than seven hours a night. So we are accruing this debt, you're racking it up, and it does have real consequences for your physical and mental health. And so, you know, when I was reporting this, I started to think like, okay, so if that if we're building up this debt, like a financial debt, how do you pay it back and so like with your finances it takes planning and sort of dedication to pay back that debt.
