Too little sleep is harmful and so is too much. We should aim for just the right amount. By Marc Wilson.
When my twin daughters were little, I was dirt poor. They have a "cool" memory of going to school with "sandwiches" made from honey between two pieces of Weet-Bix, because I couldn't afford bread that week. But, I could easily cope with the late nights and sleeplessness. Eleven years later, when their brother came along, it was the other way around – I had much greater financial stability, but the late nights were a killer. Didn't help that he hardly slept, either.
The first couple of months of looking after twins is a blur – I don't really remember much of the detail, apart from an awful lot of nappies, and that has a lot to do with the sleep thing.
When we sleep, the workers in our mental offices go home and the janitors and night shift come in to clean up. These metaphorical janitors sweep the floors and get rid of all the accreted rubbish that has accumulated during the day. The neurological equivalents of emptying the rubbish bins and cleaning up the spilt drinks are the toxins that build up during business hours and that need to be flushed away. The night shift sort through the paperwork – the memories of the previous day – and "consolidate" them, catalogue and file them away in an orderly fashion.
So, if you don't get enough sleep, not only do the day shift come in to find the place is a mess, but they can't find what they need because it hasn't been put in the right place. Hence, the brain fog and blurry memory that follow an all-nighter.
Of course, sleep is also when our batteries are recharged, and not just with the energy we need to leap refreshed out of bed. At the moment, I'm working with a Polish clinical psychologist, Marta Korporowicz, on a project looking at the role of sleep in adolescent wellbeing. As well as being a challenge to find a time that doesn't mean one or the other of us is cutting too far into our own sleep routines, we find that lack of sleep is, well, a bad thing for teens. Specifically, young people who report getting less sleep are notably more likely to report symptoms of depression and anxiety, and more likely to engage in what we call non-suicidal self-injury – hurting yourself but without any suicidal intent.
We already know that sleep is good for us, so it's no surprise to find that less sleep is bad. One important question here is why? A clue to part of the answer is this association between sleep and self-harm. One of the now-well-established "functions" of adolescent self-injury is to avoid unpleasant feelings and emotions. People are more likely to try to avoid these experiences, through self-injury or drinking or other risky behaviours, if they don't have other, safer tools in their emotional cupboard.
Unfortunately, emotion regulation is a resource that needs to be topped up regularly, including when we sleep, and what Marta and I have found is that less sleep is compromising young people's emotion-regulation toolkit. So, when bad stuff happens (being bullied, or having a fight with parents, for example), the emotion-regulation cupboard is bare.
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Sleep is also important for grown-ups. A recent really large study drawing on people in the UK Biobank database showed two interesting things. First, the relationship between sleep duration and wellbeing (broadly defined) is curvilinear – it's an inverted U-shape where too-short or too-long kips are bad. The second is that the sweet spot for those in their thirties to seventies is about seven hours, and this protects against age-related cognitive decline by keeping our brain-offices spick and span.
The take-home here is not so much early to bed and early to rise as try to have regular sleep/wake times that get you about seven hours in the Land of Nod.