Why Do We Need To Sleep?

Some animals spend over 80% of their lives asleep. But why? What’s the purpose of sleep and why does it become a problem for some people?
01 October 2013

Interview with 

Tim Quinell, Papworth Hospital


Girl asleep


Onto our main topic for the week: sleep. We spend a third of our lives doing it; in fact some animals spend over 80% of their lives asleep.

But why? What's the purpose of sleep and why does it become a problem for some people?

Priya Crosby spoke to Tim Quinell, who is a consultant at the sleep centre at Papworth Hospital...

Tim -   Sleep is about a transition from when we're fully alert and interacting sleeping commuterwith our immediate environment.  When we go to sleep, consciousness gradually drops.  There are several levels of sleep and types of sleep.  So, very light sleep isn't always perceived by someone, but fairly rapidly, at the beginning of the night, we'll go into quite deep non-dreaming sleep and it's called slow-wave sleep because the brain waves slow down.  And that's, if you like, the big money sleep that fills up the sleep bank, pays by the debt of wakefulness.  The chief drivers to sleep is how long you've been awake beforehand.  So, we're going to deep non-REM sleep and after a cycle of sleep lasting about an hour, our sleep will lighten and we will go into dream sleep and that's called rapid eye movement sleep or REM sleep.  So, that's a different type of sleep and in fact, when they've looked at brains with special imaging, during dream sleep, the brain is as active as wakefulness, but we are nonetheless asleep.  And then once we've had some dreaming, we'll go back to non-REM sleep again and the cycles continue through the night.  As the night proceeds, there is less deep sleep because the sleep bank is being filled up if you like, the debt is being paid off and there's more dream sleep.

Priya -   Roughly, how long is any one of these cycles went to a cycle of non-REM and then REM sleep?

Tim -   It's about an hour and a half to 2 hours, but it varies greatly through the nights and between individuals.

Priya -   And so, we've got a concept of what normal sleep looks like.  How do we define a sleep disorder?  I mean, a lot of us will have a night or a few nights when we struggle to sleep, but when does that what I would call normal inability to sleep become a disorder?

Tim -   All of us can have a bad night now and again.  Perhaps if we've got something big happening the next day, we might not sleep so well.  If it becomes more deeply entrenched to that, so perhaps if there's a reason to not sleep well one night, but then that reason has happened the next day, but the sleep problem persists, that might be starting to become a disorder.  It's when it becomes every several weeks or months.  That's really what I'm really talking about there is typically insomnia which is commonly experienced where people can't sleep very well at night.  But there are other disorders which typically gradually develop and they are specific disorders of breathing or where the brain's control of sleep and wake becomes dysfunctional.

Priya -   So you mentioned insomnia.  Do we know exactly what happens when someone has insomnia, we have an impression that they struggle to sleep, but do we know what's going on at a sort of more neurological level?

Tim -   There's not a lot known about why people have insomnia.  There's some evidence that people with insomnia seem to be hyperaroused.  When you look at their brainwaves during sleep, they seem to not be having such a deep solid sleep.  But there's no clear understanding as to why.  There are some other sleep disorders which present as insomnia.  For example, there's a condition called restless leg syndrome where legs are fidgety particularly later in the night when people are tired and finally lying down to go to sleep.  Their legs become uncomfortable and there's an urge to move them.  And that can disrupt sleeping causing insomnia.  And then there are other disorders of breathing where we stop and start breathing without necessarily knowing about it, but what the patient can be aware of is of poor sleep because they're constantly interrupted by the breathing pauses.

Priya -   You mentioned there problems with breathing as a disruption of sleep.  What exactly happens there?

Tim -   Sure.  So, obstructive sleep apnoea is what I'm talking about and that's probably the commonest breathing disorder during sleep aside from insomnia.  What happens with obstructive sleep apnoea is that the throat relaxes and closes or becomes very narrow, so that breathing becomes obstructed.  And so, if you like, the person suffering from obstructive sleep apnoea is choking themselves awake repeatedly during the night.  Usually, they only wake up for a few seconds so they don't remember it.  But what that means is that their sleep is peppered by brief awakenings.  And so typically, what happens if it's frequent enough is that they wake up unrefreshed by their sleep and they're sleepy during the day.

Priya -   What could they do if someone has obstructive sleep apnoea?

Tim -   People can have suggestive symptoms and we have to take them forward for test to confirm the diagnosis.  And they will look at how bad their symptoms are and how much apnoea it's occurring, how many times they stop breathing every night.  It may be that simple lifestyle measures would improve the situation.  So, mild sleep apnoea may respond to weight loss because that's a major risk factor for the development of sleep apnoea.  Sometimes it only happens when someone's lying on their back, so we can talk about measures to avoid sleeping on their back and that can do the trick.  Sometimes if sleep apnoea is more severe, then they need specific treatments.  One way of treating it is to wear a mask called CPAP which stands for Continuous Positive Airway Pressure.  This is a mask connected to an air pump which blows air through the throat to provide a pneumatic splint to the airway to stop it from flopping shut.

Priya -   If someone thinks that they might have insomnia, what options are there out there to treat or manage the condition?

Tim -   Well, many bouts of insomnia settle spontaneously so it will be short-lived and it may well relate to something that's going on in someone's life.  But if it becomes protracted as about taking a step back and looking at what things you might be doing, but aren't helping the situation - has someone got into the bad habit of working very late and then switched their lights straight out, having caffeine in the evening, or that sort of stuff, it's looking at their sleep environment, is it appropriate, is it quiet, dark, comfortable, that's sort of thing.  And also, what does happen with insomnia is it tends to feed on itself.  So, even if the initial stressor that's triggered the insomnia has been dealt with and resolved, the concerning anxiety about not being able to sleep tends to feed it.  The worst thing that can happen for insomnia is to be worried about sleeping because if we do that, then it gets worse.  And that really is something that probably most of your listeners will recognise.  If they are having a night where they're thinking about something important the next day, they're worrying about that then they realise they're not sleeping and they start worrying about that.  Sleep becomes even more elusive.

Priya -   Thanks to Tim Quinnell from Sleep Centre at Papworth Hospital.  The best thing for insomnia is actually to stop worrying about it.  Easier said than done in my own experience, I find that if you've struggled to sleep to find yourself getting into loop and you get more and more worried about it, and it stops you sleeping altogether.

Chris -   What did you think stopped you sleeping then?

Priya -   Worrying about not sleeping.

Chris -   So, what do you think got it going in the first place?

Priya -   I think shifting sleep, I think I have to get up early for a few things, and you then start thinking, well, I'm going to have 5 hours or I only got 4, and it just rolls in itself pretty much.

Chris -   I know what you mean though because when I've been in situations where you worry because you've got a big day ahead, and then you worry because you're not sleeping because you got a big day, and you are worried about being lethargic entirely the next day and then actually, worrying about not getting enough sleep takes over, doesn't it?

Priya -   Exactly.


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