Juggling sleep with work: what are the long-term effects?

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It’s 6am again. The unrelenting tone from your bedside table reminds you it’s time to roll out of your duvet cocoon and get ready to face the working world. You swat your shrieking phone as it gets louder and more persistent. A quick swipe of the screen and you notice the day. It’s Friday.

A relieved smile spreads across your face.

Well, at least tomorrow means a lie-in.

The typical working week for most will involve dragging ourselves out of our warm, cosy beds and forcing our legs to make the long cold trek to the bathroom. Yet, we know that come the weekend we will be able to catch up, even briefly, on the sleep denied to us during the week. Although we will moan to friends and colleagues, our society seems perfectly content with depriving ourselves of sleep during the working week only to catch it up during the weekend. We would likely prefer a few minutes (or hours) more in the morning, but many of us don’t consider this practice as detrimental to our health. The shift from short to long sleep is considered a part of life.

This is far from sensible as the effects of sleep deprivation are well known, even if you don’t spend your days buried in journals with helpful names such as ‘Sleep’.

There is a name (there always is) for the shifting of sleep patterns throughout the working week – social jet lag. This refers to the changes in our sleep timing and duration depending on when we’re working (e.g. sleeping less on workdays and more on free days), and how this can confuse our internal clocks which try to keep our sleep patterns regular and predictable. These are the same internal clocks which influence whether you are an owl or a lark – an evening or morning person. This misalignment affects people differently, and it is not hard to see why night owls, who want to sleep later and wake up later, may suffer more.

Social jet lag is a problem for society. It is associated with depression, an increased risk for heart disease, more frequent smoking, and increased stimulant use in general. Understandably, the effects seen from sleep deprivation, including difficulties in concentration, memory, social functioning and mood, are also associated with social jet lag.

Despite the mental and physical health issues reported, the available data had been largely correlational. This makes it hard to draw definite conclusions on whether society’s current schedule of sleep is bad for us in the long-term.

However, a recent study published earlier this year has attempted to address this.  A team of researchers at the University of Harvard sought to understand whether repetitive patterns of sleep restriction and catch-up sleep have a negative impact on our health and wellbeing, or whether we may simply get used to it.

More specifically, they wanted to try to work out whether there is a difference in our own subjective view of this sleep pattern and how our body, behind the scenes, might respond in terms of stress and immune functioning. Do we adapt to the sleep loss in both domains? Previous evidence suggested we might not but this hadn’t been convincingly tested over a long period until now.

To assess these questions, they recruited 14 participants who were studied in a controlled hospital setting over three weeks. During each week, the participants spent 5 days sleeping for 4 hours and 2 days sleeping for 8 hours. After a few months, the same participants were invited back to conduct the same experiment sleeping for 8 hours each day over the 25-day experiment. The results of each were compared to try to understand the impact of the working week’s sleep patterns.

The group asked participants about how sleepy they felt, their perceived effort to do anything, and how stressed they felt each day at 4 hour intervals throughout the study. Alongside this, objective measures of stress and immune functioning were also assessed via blood samples collected on 7 of the 25 study days. Specifically, they looked at the levels of a chemical messenger of the immune system known to promote inflammation, interleukin-6, and the levels (total and stability) of cortisol, a hormone released in response to stress (amongst other factors).

The participants’ diet and exercise were controlled to reduce the impact of these variables, and they could have visitors to reduce the impact of isolation, and deviation from normal routines, where possible.

So, what did they find?

Over the three weeks, when participants were restricted to only 4 hours’ sleep they (unsurprisingly) felt sleepier and reported a greater effort to do anything compared to when than when they could sleep for 8 hours (e.g. during the weekend in the restricted condition and every day for the control condition). Interestingly, the ‘effort to do anything’ ratings became increasingly similar for the restricted and control condition over the three weeks, and participants reported no extra stress when asked to halve their sleep to 4 hours for the restriction condition. Overall, this suggests that participants, although sleepy, were subjectively fine with the simulated typical work sleep pattern. There was even evidence that participants started to adapt as their reported effort to carry out tasks diminished by the third week of only 4 hours sleep.

By contrast, the objective results showed a less optimistic picture. The researchers found an increased dysregulation of cortisol as the weeks of sleep restriction went on, and an increase in morning cortisol compared to the control condition. However, both returned to normal following recovery sleep at the weekends. In terms of immune system functioning, unstimulated IL-6 levels were significantly higher for the first week of sleep restriction and then remained elevated but non-significantly so compared to the control condition. For the stimulated IL-6 levels, these were significantly elevated during the week for the second and third week of the restriction condition compared to the control.

These results highlight that although participants seemed to be no more stressed subjectively in depriving themselves of sleep during the week, it seems that this pattern of sleep was not something the body simply ‘gets used to’. Instead it seems that the body still shows an increase in the inflammatory marker IL-6, increased cortisol upon awakening, increased dysregulation of cortisol, and inhibition of IL-6 in the presence of cortisol-like molecule. This hints at a heightened stress and immune response which, importantly, does not appear to adapt to the effects of chronic sleep loss during the week. Although recovery sleep during the weekend mitigated this effect somewhat, there was some evidence to suggest that two days was not enough to return immune functioning (stimulated IL-6) back to normal.

You may be thinking that increases in IL-6 and increased inhibition of IL-6 seem counter-intuitive, but the authors had a potential explanation. They highlighted that this may be the product of a particularly active immune response following chronic sleep to deal with its physiological effects (i.e. the increased sensitivity to cortisol’s effect is lessened due to a need to remove toxins built up in the brain).

In addition, you may also want to argue that 4 hours sleep during the week is hardly typical of most people’s work schedule, and that this experiment is far from representative of real life. However, this is a weak argument as the effects of sleep deprivation have already shown to be cumulative. It is more likely that losing an hour or two during the workday has negative effects but over longer periods than are suggested by this study.

So, it seems that even though we may consider depriving ourselves of sleep during the week manageable, and even get used to it, the same cannot be said for our body. This study suggests that we don’t get used to sleep loss during the working week. Moreover, recovery sleep during the weekends may not be enough to compensate for a week of fighting our internal clocks.

Although this study only examined a small number of people and a small number of specific measures, it still highlights the persistent effects of restricted sleep on our immune and stress systems. It also provides some hints as to how we may be able to successfully convince ourselves that this pattern of sleep is not detrimental to our health. If we feel subjectively okay, if not slightly lethargic, about this lifestyle then there would be no immediate drive to change it – at an individual or society level.

Granted, necessity and an inability to pay the bills may also be powering this too…

Inquisitive Tortoise

References:

Rutters, F., Lemmens, S. G., Adam, T. C., Bremmer, M. A., Elders, P. J., Nijpels, G., & Dekker, J. M. (2014). Is social jetlag associated with an adverse endocrine, behavioral, and cardiovascular risk profile?. Journal of biological rhythms, 0748730414550199.

Simpson, N. S., Diolombi, M., Scott-Sutherland, J., Yang, H., Bhatt, V., Gautam, S., … & Haack, M. (2016). Repeating patterns of sleep restriction and recovery: Do we get used to it?. Brain, Behavior, and Immunity.

Van Dongen, H. P., Maislin, G., Mullington, J. M., & Dinges, D. F. (2003). The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. SLEEP-NEW YORK THEN WESTCHESTER-, 26(2), 117-129.

van Leeuwen, W. M., Lehto, M., Karisola, P., Lindholm, H., Luukkonen, R., Sallinen, M., … & Alenius, H. (2009). Sleep restriction increases the risk of developing cardiovascular diseases by augmenting proinflammatory responses through IL-17 and CRP. PloS one, 4(2).

Extra Reading:

http://www.huffingtonpost.com/margaux-mcgrath/social-jet-lag-and-sleep_b_7842074.html

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Should We Be Napping More?

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Please tweet me and other sleep scientists at the University of Manchester your sleep questions using the hashtag above! #msf16

 

“Why don’t you just take a nap if you’re so tired? It’ll probably help and give me a break from your whining…”

“I can’t nap! I feel all groggy after a nap. Besides, I find the complaining is helping me through the fatigue”

“…”

Napping is something which divides opinions. It’s no yeast-based snack featured heavily in the news recently, but there are certainly strong proponents of the will-nap and won’t-nap camps. However, what does the research say about napping? Can it help us get through the day and feel better able to deal with the challenges which face us?

Firstly, sleep in general is something taken for granted. We’re all guilty of it. On average we need about eight hours sleep, with some individual variation, but yet on average the general population is shy of this by one and a half hours. Although we should really be focusing on ensuring we get the right amount of sleep, at the right time, for our own body, it may be that napping may alleviate some of the symptoms of poor sleep such as fatigue and mood changes.

Regardless of your own personal views on this topic, it seems that naps are effective in easing fatigue, increasing our concentration, improving mood and even reaction times. Interestingly enough, even a relatively short nap of 10 minutes has been shown to improve alertness and decrease feelings of fatigue. Moreover, the positive effects were more immediate than for short (e.g. 10 minutes) compared to longer naps (e.g. 30 minutes). On a more practical level, there is evidence to suggest that a 15-minute nap could help reduce the number of road accidents.

It is key to remember that napping is a broad term. The short periods of sleep, typically during the day, which we call naps can vary in their duration and in the type of sleep which an individual might get. This could start to explain why some people love to nap and others despise it, but more on that later.

Great, so we should all be trying to sneak a nap in during office hours? Well you might want to think about the time at which you take a brief trip into sleep. During the average day, we tend to have a post-lunch dip in concentration and energy which lasts from around 1pm-4pm. Research has found that naps, whether brief or long, are most effective when taken during this post-lunch dip.

At this point, it looks like napping, albeit at the right time, can have some benefits. Yet, why might some people not actually end up benefiting? There are two possible explanations for this.

One is that disgruntled nappers may sleep for too long and focus on the grogginess upon awakening. The longer an individual naps for, the more likely they are to feel sluggish upon awakening – also referred to as sleep inertia. The positive effects of longer naps are felt for longer, but it takes longer for them to be realised.

Another explanation may depend on how serious nappers are about well… napping! Those who have more experience with napping were found to benefit more from a brief nap than those who don’t nap. This suggests that napping might have a greater effect for those who do it more frequently. Then again, it may simply be that habitual nappers are habitual because of the fact they benefit from those short slumbers. Rather than experience, it may just be individual differences. This is a question we don’t have the answer to quite yet before you try to discipline yourself into daily naps!

So what’s the verdict overall? Napping can be beneficial and if you can work through the sleep inertia longer naps will have a longer effect on your functioning. That been said, even naps as short as 10 minutes can have a positive impact. There are individual differences in our response to napping but that shouldn’t hinder us from feeling rested. Napping may be useful to ease fatigue but the ideal way to manage daytime sleepiness is to make sure you are getting better quality sleep during the night. Naps should not be a substitute for poor sleep if it can be helped!

One more thing…

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Time for ‘shameless plug time’. I am volunteering with the Manchester Science Festival as part of their sleep installation known as the Chronarium. It aims to immerse participants in specially selected lights and sounds which are used to promote relaxation and sleep. Would-be nappers are suspended in sturdy hammocks and are gently rocked into a peaceful state while the hustle and bustle of the busy shopping centre outside the fabric walls feels like a distant world.

The Chronarium is currently open as part of the Manchester Science Festival and can be found in the Manchester Arndale Centre. It is open until the 30th October. For those Mancunion readers amongst you, it’s free entry and well worth trying out!

Inquisitive Tortoise

References:

Tietzel, A. J., & Lack, L. C. (2002). The recuperative value of brief and ultra‐brief naps on alertness and cognitive performance. Journal of sleep research, 11(3), 213-218.

Brooks, A., & Lack, L. (2006). A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative?. SLEEP-NEW YORK THEN WESTCHESTER-, 29(6), 831.

Reyner, L. A., & Horne, J. A. (1997). Suppression of sleepiness in drivers: combination of caffeine with a short nap. Psychophysiology, 34(6), 721-725.

For more info on the Chronarium:

The Chronarium Sleep Lab

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Can a Lack of Sleep Kill You?

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“Have you forgotten so easily?” the subject asked. “We are you. We are the madness that lurks within you all, begging to be free at every moment in your deepest animal mind. We are what you hide from in your beds every night. We are what you sedate into silence and paralysis when you go to the nocturnal haven where we cannot tread.”

Surviving participant from ‘The Russian Sleep Experiment’ in the late 1940s. This volunteer went 15 days without sleep.

Before you start looking over your shoulder for the demonic presence presented above, don’t be alarmed. The quote above is from a piece of horror fiction from a website called Creepy Pasta and is completely fake. I hope.

I wanted to start with this as Halloween is fast approaching and I thought that a more fiendish sleep myth was worth looking at. Can a lack of sleep be directly responsible for your death?

A complete lack of sleep is something new parents and those of us with upcoming deadlines may know all too well. It’s draining, depressing, and leaves us eyeing up any available floor space as prime real-estate for your exhausted brain and body.

We have already looked at the effects of getting too little or too much sleep in my earlier post, but not the more extreme side of this. Research conducted with animals at the end of the 19th and the start of the 20th century suggests that not only is sleep important, but that it is vital for sustaining life. In experiments which looked at puppies, cats and rats, it was found that after anything from a few days to around a month of no to very little sleep would lead to death in these animals. This should be taken with a pinch of salt as animals tend to have to be forced to stay awake, and this is typically through stressful contraptions.

How about humans though? What is the longest any one has gone without sleep and gone on to tell the tale?

Well there are two main sources which we can look at. Firstly, there are the people who have willingly deprived themselves of sleep and secondly we can look at people who no longer sleep. Starting with those strange souls who willingly deprive themselves of shut-eye we can look towards a reality TV-show, our trusty sleep-deprived student population, and a couple of radio DJs to start to answer this question.

People are seemingly keen to show off their endurance when it comes to neglecting or overindulging in the necessities of life. Some will do it to win a fabulous prize and others because… Well I’m sure they know why they do it. Anyway, one such contest is relevant here.

The reality TV show ‘Shattered’ provided contestants a chance to win £100,000. All they had to do was be the last one standing in a competition to stay awake the longest. The show was screened on channel 4 in 2004 and its questionable premise didn’t put off a group of eager participants keen to deprive themselves of sleep for fame and glory. The winner stayed awake ultimately for 178 hours. The show capped the length of time participants could remain awake for, and a number of increasingly soporific tasks eventually weeded out one overall victor. If you are interested in this ‘experiment’ you can watch it here.

However, 178 hours was meagre compared to the next contenders. It seems that at the end of the 1950s and early 1960s there was a surge in radio DJs attempting to promote themselves and further their careers in bizarre ways. Collectively they felt that staying awake and parading their increasingly fatigued selves in a department store window was the way to do this.

Our first member of the media to tackle a lack of sleep was a young radio announcer referred to as W.A. He managed to stay awake for a total of 220 hours or just over 9 days. Previously, another radio DJ by the name of Peter Tripp had managed to last 201 hours without sleep. Finally, our last radio DJ, Tom Rounds, shortly after moving to Honolulu in 1959, managed to stay awake for 260 hours and appeared to suffer no long-term effects of his sleep deprivation.

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Is sleep necessary for sustaining life?

However, their collective records did not last long. The radio DJs were swiftly beaten in 1964 by the efforts of a student called Randy Gardener. Randy was a 17 years old student who felt that he could provide something more interesting than a papier-mâché volcano to present at his school’s science fair. He went without sleep for 264.4 hours, which equates to about 11 days and 24 minutes, and supposedly suffered no long-term problems. The often cited report claims that Randy suffered no ill effects of his experiment, yet others claim he experienced hallucinations, paranoia, fluctuations in mood, and problems in short term memory and concentration. The latter would fit with what we know about acute sleep disturbances (Petrovsky et al. 2014; Kahn-Greene et al., 2007).

Interesting, there have been reports of others having seemingly beaten Randy’s record and by a sizeable margin. These have not been validated in part due to scientists and those responsible for recording ‘world records’ not wanting to encourage these record attempts. For example, the Guinness Book of World Records no longer prints updates to the sleep deprivation record since Randy Gardener.

Okay, so far it looks like we can go a long time without sleep and survive. This seems to suggest that although we need sleep (try not sleeping tonight if you’re not convinced), an acute loss is not going to be directly responsible for your demise (but likely indirectly).

Let’s move to the second source of human sleep loss evidence now: those who no longer possess the ability to sleep.

We’ve already looked at people who for one reason or another have decided to willingly deprive themselves of sleep. Yet, for some the ability to sleep is lost. Although insomnia fits this bill, in this case we are referring to the rare genetic brain disease known as Fatal Familial Insomnia (FFI). As the name suggests, this disease is associated with a prolonged and severe insomnia which ultimately leads to death. There are some experimental treatments to delay the fatal consequences but these may only provide a couple of extra years at best.

Fatal familial insomnia is a prion disease. Prions are misfolded proteins that cause damage to the brain as they clump together. In the case of FFI, these prions clump at a specific part of the brain known as the thalamus. The thalamus plays a prominent role in regulating sleep and in coordinating the brain as it drifts deeper and deeper in somnolence. As a result, as the damage to the thalamus accumulates this unsurprisingly leads to worsening insomnia.

These individuals seemingly sleep very little or not at all and will survive from a few months to about several years following the presentation of symptoms. The course of this illness would suggest that it is possible to die from sleep deprivation, at least at extreme durations. However, we can’t say that it is the complete lack of sleep alone which kills those with FFI as damage to the thalamus affects other functions rather than just sleep. Moreover, as this disease is so rare that it would be wrong to make a firm conclusion based on this alone. More likely, it seems that the lack of sleep contributes significantly, but not completely, to the decline of those with this illness.

So, what’s the verdict on sleep deprivation being capable of deadly consequences?

The research in animals suggests it can be but the human studies tell another story. Although common myths and horror stories might like to toy with our inbuilt fears about the unknown, it looks like a lack of sleep will not directly lead to your death. Instead, the host of effects already covered may be the true driver between mortality and sleep loss.

Inquisitive Tortoise

References:

Luby, E. D., Frohman, C. E., Grisell, J. L., Lenzo, J. E., & Gottlieb, J. S. (1960). Sleep deprivation: effects on behavior, thinking, motor performance, and biological energy transfer systems. Psychosomatic Medicine, 22(3), 182-192.

Petrovsky, N., Ettinger, U., Hill, A., Frenzel, L., Meyhöfer, I., Wagner, M., … & Kumari, V. (2014). Sleep deprivation disrupts prepulse inhibition and induces psychosis-like symptoms in healthy humans. The Journal of Neuroscience, 34(27), 9134-9140.

** http://creepypasta.wikia.com/wiki/The_Russian_Sleep_Experiment

**In case you find yourself wanting to read the rest of the fictitious foray into the effects of sleep deprivation.

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Why Do We Sleep? Keeping Those Pesky Excitable Neurons in Line

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“The subject of sleeplessness is once more under public discussion. The hurry and excitement of modern life is quite correctly held to be responsible for much of the insomnia of which we hear: and most of the articles and letters are full of good advice to live more quietly and of platitudes concerning the harmfulness of rush and worry. The pity of it is that so many people are unable to follow this good advice and are obliged to lead a life of anxiety and high tension. Hence the search for some sovereign panacea…” (British Medical Journal, SEPT. 29, 1894, Sleeplessness)

I am sure until you glanced at the date you could easily be forgiven for thinking this quotation was written only last week. The disturbance of “modern life” is far from a novel phenomenon that plagues the 21st century, and smartphones and technology cannot be solely to blame for the problems we see. As the quotation continues (you can read the full article here, page 719), it is clear that attempts to treat insomnia were not all that different from remedies people might turn to now.

Disturbed sleep is something we’ve all experienced at one point or another. That sleepless night before an important meeting, interview, or exam stress leaves us feeling groggy, less responsive, and annoyingly less prepared for the problem we have to face. It’s clear that even a night of poor sleep can cause a plethora of problems which make restoration theories of sleep enticing and convincing. However, it is still not certain how sleep might rectify the impaired functioning associated with a night of tossing and turning in bed.

One theory argues that sleep acts to quieten down brain activity which becomes increasingly noisy during the day. This ‘noise’ makes it harder to function in terms of laying down new memories, remaining vigilant, and maintaining a positive mood. There are plenty of studies which highlight problems in each of these areas following poor, or a complete absence of, sleep for even a single night.

Now, the brain is a noisy organ and is constantly busy keeping you alive and functioning. Even when you’re not ‘thinking’ anything, it is still possible to detect a network of activity associated with this resting state. However, when ‘noisy’ is used here, it is in reference to noise which may be more indiscriminate and impede normal brain functioning.

Synaptic Homeostasis Hypothesis

This theory is known as the synaptic homeostasis hypothesis and was put forward in 2003 by the psychiatrist, Dr. Giulio Tononi of the University of Wisconsin-Madison. This theory centres on the important role of slow wave sleep (SWS) during a night’s sleep. SWS is the predominant neural signal found during the third stage of NREM sleep, and is characterised by slow-synchronised oscillations across the cortex. It is associated with the deepest stage of sleep and with many restorative properties of sleep.

A paper by Christoph Nissen and colleagues, published just this week in Nature Communications, has shed more light on how sleep may help us function on a day to day basis, and has provided further support for the synaptic homeostasis hypothesis. Currently, most of the evidence for this theory comes from animal studies and indirect evidence from a handful of human studies. That is what made the recent study by Nissen particularly exciting.

Christoph Nissen and colleagues at the University of Freiburg explored how sleep, compared to sleep deprivation, was associated with changes in memory encoding, cortical excitability and neural mechanisms behind brain plasticity and learning. They examined a group of 20 healthy university students who all took part in the normal sleep and sleep deprivation portions of the experiment.

The team examined cortical excitability following a normal night’s sleep and sleep deprivation using transcranial magnetic stimulation (TMS) to induce a twitch in a participant’s hand. The TMS device allows scientists to deliver a pulse which can be used to inhibit or excite the neurons underneath its coil. A pulse to the appropriate location on the right side of the brain will produce a corresponding twitch to the muscle in the participant’s left hand. The strength of the pulse needed to produce a response, or twitch, can be used as a marker of how excitable that particular patch of neurons is. As a result, this technique provides a non-invasive and relatively simple way to test one of the synaptic homeostasis hypothesis’ predictions.

In addition, the group examined brain activity using electroencephalography (EEG) to further explore alterations produced by extended wakefulness.They also tested performance by examining participant’s memory through the use of a simple word pair test, and through their capacity for LTP-like plasticity using a paired stimulation method.  LTP, or long-term potentiation to give it its full name, has been argued to be the mechanism within the nervous system through which learning occurs. It is argued to play a large role in memory formation and so provides the researchers with another way to assess performance following extended wakefulness or sleep.

In their student sample, Nissen and colleagues found evidence of increased cortical excitability, poorer memory performance, and reduced LTP-like plasticity following a night of sleep deprivation compared to wakefulness. All of these support the synaptic homeostasis hypothesis and support the role of sleep in ‘resetting’ the neural activity to a baseline. It is argued that this is what allows us to continue on at our best after a night’s sleep and allows us to start efficiently storing memories of cute animal videos while at work.

Yet, the evidence for this is still in its infancy and it would be unwise to jump to conclusions about this research. Rather, it is another hat to throw into the ring of sleep science.

This work is still just a start, but it is an interesting and exciting foray into further understanding how sleep serves its important role in our lives. Furthermore, it also provides some interesting avenues for therapies which might try to capitalise on the ability of sleep to return neural activity to a set-point. There is already some evidence to support short-term sleep deprivation to help depression. A further understanding of sleep’s impact on the brain, or lack thereof, may help us manipulate this to our advantage.

Inquisitive Tortoise

References:

Kuhn, M. et al. Sleep recalibrates homeostatic and associative synaptic plasticity in the human cortex. Nat. Commun. 7:12455

Tononi, G., & Cirelli, C. (2003). Sleep and synaptic homeostasis: a hypothesis. Brain research bulletin, 62(2), 143-150.

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Why Do We Sleep? The Brain’s Waste Disposal System

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How does sleep help this fellow’s tubular brain remain healthy?

“Okay, smart guy so why do we sleep then? Bet you can’t answer that one…”

“Well… How long have you got? There’s a fair bit of content to co- Hey! Don’t run away! It won’t take me that long, honest!”

Sleep is complex and despite the intuitive explanation for why we drift off on a daily basis, we are still in our infancy when it comes to understanding how and why this occurs. We know that for the most part a good night’s sleep is refreshing and important for paying attention at work, school, or carrying out most tasks.However, how sleep keeps us functioning is less black and white.

There is no one reason why we need to sleep. For example, it maintains us mentally and physically in a number of ways, including:

  • Memory consolidation
  • Growth
  • Mental health
  • Brain maintenance

We could spend a lot of time covering all of these in considerable detail, but for now we’ll look at brain maintenance. Brain maintenance may seem like a broad category but it fits into our recent developments in understanding how the brain deals with waste materials.

The Brain’s Waste Disposal System

All cells in the body produce waste products of some description. This may be as a result of metabolic functioning, protein synthesis, and cell death, and these are filtered out via the lymphatic system.

The brain, unsurprisingly, is no different. However, until recently it was not clear how the brain solved this waste management problem. That was until the recent discovery of the glymphatic system.

Glymphatic System: The Brain’s Clearance System?

So what is the glymphatic system, and why should we care? Well firstly, its discovery has been hailed as important step in understanding major neuropathologies such as Alzheimer’s disease. Although, there’s a while to go before we should get too excited about this.

As mentioned above, the cells within your body work and produce potentially toxic waste products. The body has an effective way of getting rid of these through multitudinous lymphatic vessels. Yet, until recently it wasn’t known how the central nervous system, that is the spinal cord and the brain, manage to remove their waste products.

In a similar way to the lymphatic system, it has been proposed than the glymphatic system works by removing waste products from the central nervous system (e.g. spinal cord and brain). This is achieved, in part, by the exchange of solutes or waste products between cerebrospinal fluid (CSF) and interstitial fluid (ISF).

The system is comprised of a series of channels which appears to “piggyback” off blood vessels within the brain. It is argued that the movement of arteries, as a result of blood-flow, helps to move the cerebrospinal fluid through the brain (CSF). This enables the movements of waste between interstitial fluid (ISF) which bathes cells and CSF which runs alongside blood vessels in the brain. However, the glymphatic system also includes the presence of specific glial cells, known as astrocytes, alongside these channels. The function of the astrocytes is to facilitate the movement of particles between CSF and ISF. Without their presence, the movement of waste would be too sluggish to respond appropriately to the changing demands of the hungry organ we call the brain. It is the presence of glial cells, and the similarities to the lymphatic system, which give this glymphatic system its name.

Waste Disposal While You Sleep

How does all of this relate to sleep? Well, a recent collection of studies has provided some evidence that sleep may facilitate the movement of toxins from the brain via the increased activity of the glymphatic system.

One particular toxin produced as a waste product of brain cell activity is called amyloid beta. This toxin is linked to severe progressive diseases such as Alzheimer’s, and there is considerable research trying to work out how to mitigate its destructive effects. Last year, a group of scientists lead by Professor Maiken Nedergaard at the University of Rochester Medical Centre found that the brain’s drainage of amyloid beta was increased during sleep and anaesthesia-induced unconsciousness compared to during wakefulness in mice. More specifically, it seems that the capacity of the brain to flush out such harmful toxins is enhanced due to the area between cells, interstitial space, expanding by as much as 60 per cent. This seemingly enables a greater opportunity for such toxins to be removed via the glymphatic system.

In addition, the same group also found earlier this year that this process of washing harmful toxins out of the brain during sleep is enhanced based on the position of the mice studied. It was found that the removal of amyloid beta was enhanced when the mice slept on their side rather than their back. Interestingly, in both cases, it seems that anaesthetised mice showed the same effects as sleeping mice for the removal of amyloid beta and benefit of sleep posture.

This suggests that sleep may help with the maintenance of our brains by enhancing the waste disposal system we have in place. It may also provide some evidence as to why dementia and serious psychiatric illnesses are associated with sleep disturbances prior to the emergence of symptoms. However, this is all speculative and uncertain at this point. For a start, these studies have only been conducted on mice, and due to the nature of the experiment it is not likely that they would be conducted on humans any time soon. That’s not to say that the same mechanism might not be occurring within humans, but it is rash to jump the gun and assume it is.

Regardless, it will be exciting to see how research in this area advances and what it can teach us about the importance of sleep.

Inquisitive Tortoise

References:

Lee, H., Xie, L., Yu, M., Kang, H., Feng, T., Deane, R., … & Benveniste, H. (2015). The effect of body posture on brain glymphatic transport. The Journal of Neuroscience, 35(31), 11034-11044.

Xie, L., Kang, H., Xu, Q., Chen, M. J., Liao, Y., Thiyagarajan, M., … & Takano, T. (2013). Sleep drives metabolite clearance from the adult brain.science, 342(6156), 373-377.

Further Reading:

https://www.urmc.rochester.edu/labs/Nedergaard-Lab/projects/glymphatic_system (From the horse’s mouth; a better description of what I’ve tried to convey in this post!)

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Sleep Roundup 12/07/16

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So, being the geek that I am I come across lots of interesting sleep talks online and resources which help me with my day to day research. Here’s a roundup of the current sleep talks / podcasts online over this past week or so which grabbed my attention.

This may become a regular thing if I find enough interesting sleep research / talks (organisation permitting, no doubt).

For now enjoy two the latest episode of the Infinite Monkey Cage which is focused on sleep in general and How Much Sleep Do We Need from the BBC. Also, if you don’t already listen to the infinite monkey cage, do so now!

Inquisitive Tortoise

 

 

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Sleep Trackers: Do They Work?

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“What makes a good sleep tracker?”

“I didn’t sleep too well last night, and I felt so groggy this morning”

“Stressful day at work?”

“No, my stupid SleepApp didn’t work properly and I spent the night trying to get it to play relaxing whale noises. When I did drift off by myself, it didn’t wake me up in between sleep cycles. It better not fail tonight, I’ve got an important meeting tomorrow and I can’t sleep properly without it…”

“Uh-huh…”

Stilted conversation aside, we spend a large amount of our daily lives glued to screens of some description. These keep us active and engaged well beyond the time when we should be switching off for the night. For example, light from phones and laptops can alter our normal patterns of sleep and make it harder for us to drift off in the evening. This plays havoc with the body’s multitudinous clocks which naturally set in motion a number of chemical changes that allow us to unwind steadily before we drift off to sleep. However, that’s a point for another day.

For now, I want to talk about how we use technology to seemingly help us get to sleep and to, in want of a better way of putting it, tell us that we were in fact asleep the previous night (with or without a pretty graph to go with it).

Commercial ways to assess sleep:

There were two main ways of objectively measuring sleep in the research community: actigraphy and polysomnography (See what makes a good sleep tracker?) However, the business world has managed to split this up into a large selection of methods to tell us whether we’re sleeping enough. It may be that these different commercially available devices and apps are actually pretty good but the available evidence tells a different story.

Types of Sleep Tracker

I won’t go into too much detail about all of the different types of sleep tracking devices, of which there are many, but the purpose of the below list is to show the range of ways you can measure your sleep outside of the lab.

Movement-Based

Sleep apps developed for use on phones (e.g. Android or Apple stores) vary in cost and features which they promise. A popular sleep app for android users, ‘Sleep as Android’, has over 10 million downloads and boasts the ability to differentiate between wakefulness, light sleep and deep sleep. It also claims that it can wake you up during your lightest sleep stages in the morning to promote a “natural” awakening which supposedly avoids the grogginess and tiredness of waking up in the deeper stages of sleep. This app, amongst others, relies on movement-based information.

Movement-based trackers can also take the form of watches which track our sleep (alongside activity, exercise, and heart rate). Both of these aim to give us lots of detail about our sleep and provide us with statistics which try to educate us about our own sleep – mainly with the intention of helping you sleep better. These works by applying an algorithm to movement data which is logged by something called an accelerometer. This is already present in your mobile phone and the app simply makes use of this data to predict your sleep.

Brain-activity Based

There are a number of devices which you can buy which will offer a rudimentary attempt to track brain activity. Typically, if you want a good picture of your sleep you will track a wide range of different bodily functions in something known as polysomnography (see what makes a good sleep tracker?) However, these trackers try to track sleep through the use of a couple of electrodes placed on the scalp during sleep.

Temperature / Heart Rate / Muscle Response Based

Typically, these will be used alongside movement data to attempt to give a more accurate estimate of sleep.

Bed-Based

Again, these are technically based on movement and temperature data but are placed on the bed in some respect and not worn. These can take the form of a bed covering (link), or even a trendy looking ball such as Sense.

What makes a good sleep tracker?

So what does an ideal measurement of sleep look like?

Polysomnography

The gold-standard measure of sleep is known as called polysomnography. This measures a number of different things including:

  • Electroencephalogram (EEG; records electrical activity produced by cells in the brain)
  • Electrooculography (EOG; records eye movements)
  • Electromyography (EMG; records electrical activity generated by muscle activity)
  • Cardiac rhythms (ECG)
  • Respiratory activity

This setup, understandably, requires you to come into a sleep laboratory and sleep in a rather unfamiliar bed with electrodes planted on your head and body. This enables sleep researchers to record brain activity, eye movements, muscle activity and heart rhythms. Together, these readings allow us to identify how long you sleep, how often you wake up, how long it takes for you to get to sleep, when you wake up, and to identify the individual sleep stages and cycles which make up a normal night’s sleep. There are problems with this approach but it is the best option we have for understanding more about an individual’s sleep. As you’ll likely agree, this is a lot of information to obtain and wade through. Sleep apps and watches cannot possible recreate this and so are limited, but this is not necessarily a problem if they correlate well with other less rigorous but well accepted measures used in sleep research.

For example, most sleep apps and watches work by determining how often you move on a given night and use the times you are moving less as sleep and the times you are moving more as awake. These devices measure movement by using a little device called an accelerometer which is found within your smartphone and watches such as the FitBit.

Actigraphy

Within sleep research, we also use a device which is based on this same technology. The device is known as an actigraphy watch and it is generally seen an acceptable alternative to sleep lab measurements which are often costly, time-consuming and cumbersome. An actigraphy watch is usually worn on the non-dominant wrist, can be used outside a sleep lab, and thus allows researchers to assess sleep objectively as people go about their normal day-to-day lives. Actigraphy also works by detecting movement through accelerometers, and algorithms are applied to this data to explore certain facets of sleep (there are limits to this) in a more portable format.

Do these sleep apps actually work?

The main question you’ve probably come here to hear answered. The short answer: yes, but there are limitations to them all.

Quite simply put, there is a lack of research conducted here and the sample sizes are miniscule at best for the ones that do currently exist. Yet, these research studies do hint that perhaps sleep apps and wearable devices are actually assessing your levels of sleep in terms of duration, sleep efficiency and how often and for how long you are awake during a night of recording.

When sleep researchers try to determine whether wearables are actually tracking sleep they look for the following things: sensitivity (e.g. the ability of the app / device to measure when you’re actually asleep), specificity (e.g. the ability of the app / device to measure when you’re actually awake) and accuracy (e.g. is it measuring when you’re truly awake and truly asleep).

What does the current science say about commercial sleep trackers (e.g. FitBit)?

Wearables, or commercial sleep trackers, tend to show the same pattern when it comes to estimating our sleep patterns as that which is seen in actigraphy. Wearables using movement data typically overestimate total sleep time and sleep latency (how long it takes you to fall asleep) but are generally pretty accurate at telling when you’re asleep and for how long. By contrast, wearables such as the FitBit are poor at identifying periods of wakefulness during the night and will significantly underestimate disruptions in the night – known as wake after sleep onset (WASO). So, for the average person it is fair to say that wearables such as the numerous reincarnations of the FitBit may give you some insight into what your sleep looks like. However, if you are prone to fitful sleep or suffering from insomnia then these apps will be less accurate (despite claims on FitBit’s website that they may have a fix for people with disrupted sleep) and should not be depended upon. This is doubly the case if you consider using these in lieu of a going to a doctor about your sleep issues.

How about the claims made by, worryingly, many sleep apps and wearables that they can track different stages of sleep? The bold claim that a sleep app can measure REM sleep, for a start, is simply not known and extremely doubtful, even if some apps do add in more than just movement measures (e.g. heart rate). Other wearables such as the Jawbone UP make more reasonable claims that they can detect “light” versus “sound” sleep over a given night. Although it’s not entirely clear what “sound” sleep actually means, one research team took this to mean deep sleep and examined whether there was any truth behind this claim. In a large sample of adolescents, they found that the light and sound sleep measures were rather poor at measuring what they claimed to. Rather worryingly the ‘light’ sleep was found to be associated with time spent in the deepest stage of sleep which highlights that healthy skepticism should be applied to apps claiming they can pick out individual, or broad, sleep stages (see further reading).

Further Reading

A study by de Zambotti and colleagues examined the sensitivity and specificity of a different wearable, the Jawbone UP, compared to polysomnography and actigraphy in a group of middle aged women (average age 50 years old). They found, like others, that the Jawbone UP was generally accurate at determining when and for how long participants slept (but overestimated this value), but was pretty poor at determining when participants woke up during the night (underestimated this value, so had a good sensitivity but poor specificity). The ability to detect periods of waking and total sleep during the night were notably bad during particularly disrupted sleep as detected by PSG. This suggests that the Jawbone UP and FitBit Ultra are not particularly accurate at detecting the amount of sleep and waking in individuals with disrupted / fragmented sleep.

When the same research group (de Zambotti et al., 2015b) also examined the Jawbone UP in a sample of adolescents and young adults (age range 12-22 years old) and found similar results. That is, that the Jawbone UP overestimated total sleep time, sleep efficiency and sleep onset latency but underestimated total wake time during the night (it was much worse at detecting time spent awake than any of the sleep measures). Overall, it was found that the Jawbone UP was good at detecting when participants were asleep, but rather poor at identifying when they woke up during the night. This is important as fragmentation of your sleep will impact on sleep quality.

The same study also tried to examine whether the Jawbone UP’s dichotomisation of ‘sound sleep’ versus ‘light sleep’ were appropriately linked to deep versus light stages of sleep as assessed in the sleep laboratory. The ‘light sleep’ count was linked to movement and awakenings, and also to stage 3 of sleep (known as the deepest stage of sleep). In fact, none of the lightest stages of sleep were shown to be associated with the ‘light sleep’ count produced by Jawbone UP. The opposite was found for the ‘sound sleep’ count whereby typically deep stages of sleep were not found to be associated with this measure, but rather overall measurement of movement (specifically reduced movements) was. This suggests that wearables such as Jawbone and FitBit may be reasonable at detecting sleep during the night, but not night-time awakenings or the different stages of sleep. Furthermore, in populations where sleep is fitful or fragmented the accuracy of these apps reduces to a greater extent.

A previous study by one of the study’s authors, Hawley Montgomery, in 2012 found that a wrist-worn FitBit was comparable to actigraphy, but poorer than polysomnography in detecting when people were asleep. However, the FitBit was particularly poor in identifying when people woke up compared to actigraphy. This suggests that the healthy adult populations could still gain useful information from a FitBit but, as the authors highlight, it is a far way off being appropriate for measuring sleep in people with diagnosed or suspected sleep disorders.

As you can hopefully see, there are only a handful of studies which have attempted to understand how good market-leading wearables are in detecting sleep and wake. The emphasis on sleep and wake is intentional. These apps have not been assessed for their ability to assess anything beyond total sleep time, wake after sleep onset, sleep onset latency and sleep efficiency.

Smart Alarms

Other sleep apps also include a measure to wake individuals up during the lighter stages of sleep to enable them to feel more wakeful in the morning. The alarm sounds after tracking an individual’s pattern of sleep to create an ‘optimal’ window to wake up during which the alarm will try to target. Alarm PicHowever, there is currently limited evidence to back up these claims (Kelly et al., 2012), and there needs to be considerably more research here before such claims can be validated and backed up (SLEEPIO Article). It is somewhat surprising that such research has not been carried out considering how easy it would be to create an experiment where participants are randomized to either an optimal or sub-optimal wake-up alarm condition over 1-2 weeks (See Kelly et al., 2012 for expansion on this very point).

Concluding Thoughts

Sleep is something which can be fickle at many times throughout our lives, and it is not surprising that we would want to learn more about it. However, for those of us who suffer with our sleep on a regular basis, there is an obvious appeal to be able to track our sleep in the comfort of our own homes and on a regular (perhaps even nightly) basis. It may provide a skewed notion of how an individual is sleeping (for better or for worse) and this can provide unfounded alarm or comfort. The current wearables have a reasonable ability to tell when and for how long you’re asleep but be sceptical on their ability to tell you anything about the quality of your sleep. If you are genuinely concerned about your sleep then please consult your doctor.

Sleep apps, wearables and other sleep trackers are a fantastic idea and if they can prove to be comparable to other methods such as actigraphy then I see few reasons to discourage their use. However, there is a lack of available data to really understand whether these different sleep trackers are accurate. If they are simply measuring time spent asleep and awake then they seem to be okay, and comparable to measures used in sleep experiments. Yet, bolder claims about smart alarms, tracking individual sleep stages, and their use in sleep disorders are not conclusively studied at this moment in time. That is not to say they will not, but there is a sensible reason to be cautious until that evidence is available to us. So, by all means use these trackers and add them to part of your daily routine if you so wish. However, understand their limitations and be aware that paying minute detail to your sleep may also create its own problems. More on that point in my next post.

Inquisitive Tortoise

References

de Zambotti, M., Baker, F. C., & Colrain, I. M. (2014). Validation of Sleep-Tracking Technology Compared with Polysomnography in Adolescents. Sleep, 38(9), 1461-1468.

de Zambotti, M., Claudatos, S., Inkelis, S., Colrain, I. M., & Baker, F. C. (2015). Evaluation of a consumer fitness-tracking device to assess sleep in adults. Chronobiology international, 32(7), 1024-1028.

** Kelly, J. M., Strecker, R. E., & Bianchi, M. T. (2012). Recent developments in home sleep-monitoring devices. ISRN neurology, 2012. (Good expansion on the different sleep trackers available)

Montgomery-Downs, H. E., Insana, S. P., & Bond, J. A. (2012). Movement toward a novel activity monitoring device. Sleep and Breathing, 16(3), 913-917.

Montgomery-Downs, H. E., Insana, S. P., & Bond, J. A. (2012). Movement toward a novel activity monitoring device. Sleep and Breathing, 16(3), 913-917.

Further Reading

http://www.huffingtonpost.com/dr-christopher-winter/sleep-tips_b_4792760.html

https://www.sleepio.com/articles/sleep-aids/sleep-apps/

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The Science Room

I recently wrote another science thing! This time it’s not about sleep but I imagine it’s something which some of you will find interesting. Please check it out and make sure you direct any interesting science questions to the Science Room too!

http://sciroom.org/articles/how-do-mirror-neurons-work

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Somniloquy: What causes sleep talking?

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Sleep(ing) is tricky.

We’ve already covered sleepwalking in some detail and identified how complex behaviours can be initiated during a period of seeming unconsciousness. These behaviours can take a wide range of different forms. For example, reports of sleep-texting are becoming more common, which highlights how changes in our daily routines lead to changes in the type of sleepwalking behaviours. Next on our list is to shed some light on why we might talk in our sleep too.

“Jack…? Are you awake? What’re you talking about?”

“Ignore him, he’s speaking in devil-speak again. He does that.  Admittedly, it’d be less freaky if he didn’t have his eyes open at the same time too…”

Apparently I didn’t form full sentences in my sleep during my spate of sleep-related weirdness as a child, but sounds resembling more than mumbling could be identified by friends whenever I stopped over. Alongside the heart-attack-inducing brush with sleepwalking which my parents were forced to endure, I also ‘entertained’ my friends by talking in my sleep – or engaging in somniloquy, as it’s also known.

Sleep talking is an experience which many of us will come across at some point in our lives.  It is a relatively common phenomenon and can be found predominantly during childhood, but also as a rarer occurrence within adulthood. However, the prevalence in adulthood varies considerably. It is one of the most frequent parasomnias (disorders of sleep which involve some form of unusual or unwanted behaviour during sleep) found between the ages of 3-13 years old (Laberge et al., 2000), and it appears slightly more often in boys of this age than girls.

Sleep talking is associated with sleepwalking, and one may predict the subsequent occurrence of the other (Ohayon et al., 1999). This is not surprising, as many parasomnias are found together, or increase the likelihood of someone experiencing another. The main concern during adulthood is the potential embarrassment which might come alongside the sometimes nonsensical muttering, and potentially the content which is said. However, it is generally accepted that sleep talking, although impressively coherent at times, is not necessarily truthful or meaningful. For example, it is not admissible in court and the individual will have no memory of what they said or even that they were talking in their sleep. This is part of the reason why it is so tricky to work out the prevalence of sleep talking in adults.

When does sleep talking occur? Well, like many other parasomnias, it appears that it can occur across the sleep-cycle. The quality and coherence of the speech during sleep may differ as an individual goes from light, deep and finally to REM sleep. The exact link between sleep stage and speech is uncertain, but it has been argued that REM sleep is associated with more coherent and daytime-like conversations. There is also evidence to suggest that it runs in families, although environmental factors may make it more likely.

What causes sleep-talking and should we be concerned? For the majority of us, no. It is a harmless, if amusing, occurrence and may only occur in episodes which can be traced to an environmental cause. For example, it can be brought on by a number of factors such as sleep deprivation, stress, alcohol and fever. However, there may be problems associated with the effect of sleep talking on a bed-partner. This may produce problems in the person who shares the bed with the sleep-talker, who may find themselves being kept up and experiencing insomnia-like symptoms. Some studies have highlighted a link between adult sleep talking and some psychiatric illnesses, but it is far from conclusive what the nature of this link is. For the most part, sleep talking is a harmless, if slightly embarrassing, behaviour.

Sleep talking can also occur in the context of other illnesses such as night terror, nightmares, sleep apnea and REM behaviour disorder (RBD).

Other areas in which sleep talking may occur:

Night Terrors

One way in which we can explore sleep-talking is in the presence of noted disorders during sleep. One example, where sleep-talking and movement are found, is night terrors. These are a form of sleep disturbance which occurs mainly during childhood. They are characterised by thrashing, panicked-like behaviour and screaming which occurs for several minutes. The child has no memory of this, and it can be considered a disorder of arousal like sleepwalking. In a similar manner, they can be exacerbated by anxiety, poor sleep schedules and behaviours which disrupt sleep (e.g. needing to go the toilet). Although this is not your archetypal description of sleep-talking, it is an example of how the boundaries between sleep and wake are blurred.

REM Behaviour Disorder

This is another disorder of arousal and, like night terrors, also involves elaborate movement and speech during a period of sleep. This occurs more commonly during middle age and is associated with more insidious origins such as the onset of Parkinson’s disease. At a basic level, RBD can be considered the acting of dreams, and the behaviours shown typically match with dreams had by the individual with RBD. However, dream ‘enactment’ can occur alongside many other sleep disorders, and the diagnosis of the disorder needs to be confirmed with the use of methods to study brain and muscle activity during sleep.

It’s important to note for that all the knowledge which we have amassed on the topic of sleep, we are still uncertain about so many different aspects of it. Sleep-talking fits into that snugly, and although I can provide indirect forms of evidence about what causes sleep-talking, it is very much left to scientists to further explore disorders of arousal and explore their causes in more detail.

Inqusitive Tortoise

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How Much Sleep Do We Need?

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Despite our urge to squeeze everything out of the day, sleep is something we cannot live without.

As I start to think about this question, I can feel the inner scientist in me asking a range of questions in response to your first. Sadly, I have a limit to how long my response should be before people start turning off… So, to prevent his becoming a short thesis in itself (or several), I have opted to approach this question in terms of a healthy adult and to focus on how much sleep we need to remain physically and mentally healthy, and not just simply survive.

It is important to ask how much sleep we really need, and just as important to make sure we actually try to achieve this. As we’ll see, sleep is vital for the healthy functioning of many physiological and mental faculties that to skimp on it is inexcusable. As I type this, I can hear many crying out “modern living”, “deadlines”, “fitting everything in”, and even the faint whispers of “YOLO” on the breeze. However, sleep is not simply an inconvenience to our daily lives but an important part of keeping us functioning.

To highlight this, let’s look at the effects of a lack of sleep. A chronic lack of sleep has been shown to be associated with heart disease, type 2 diabetes, and stroke to name but a few. It should also be noted that there’s such a thing as ‘too much’ of a good thing, as excess sleep is associated with similar problems as too little sleep (Shen et al., 2016). At some point, you have probably felt the effects of lying in for too long and the scourge of ‘sleep hangovers’.

How do we measure an ‘optimum’?

There are a number of ways we can do this, but first we need to understand what we mean by optimum and why we sleep in the first place. The exact function of sleep is still not fully understood but it is generally agreed that sleep enables us to grow, is vital for memory and keeps us alert and healthy. In fact, prolonged durations without sleep can distort our perception of reality, interfere with our memory in a staggering way and, in very extreme cases, lead to death.

By looking at this in the long-term, we can identify the ‘optimum’ amount of sleep by observing lots and people’s sleep habits and to identify the risks associated with differing hours of sleep. We can also deprive individuals of sleep and see how they function after a couple of hours (or complete) sleep restriction compared to a normal night. For example, if we deprive someone of 1 or 2 hours sleep per night do we see any effect of an individual’s ability to function during the daytime? If the answer is yes, then this would suggest that those extra hours of sleep are important to us in some way.

So, we are now more familiar with why we should attempt to get the right amount of sleep, and how to measure the importance of sleep, but how much do we actually need? The simple answer is that 7-8 hours is generally considered to be ideal for the majority of individuals. A recent study highlighted that 7 hours was optimum for avoiding the negative impacts of too little or too much sleep (Shen et al., 2016). Another comprehensive review highlighted again that between 7-8 hours was optimum when considering all-cause mortality (i.e. your chance of death is reduced if you get between 7-8 hours of sleep a night, when compared to more or less sleep).

What about those who can survive with less than 7 hours?

However, although there is some merit in this claim, it has created the idea that there is a ‘perfect’ amount of sleep, and that this is the same for everyone. This really is not the case and the amount of sleep an individual ultimately needs to feel refreshed and to function varies from person to person. To many sleep scientists this is source of frustration and avid fascination. Take, for example, individuals who only need 5-6 hours of sleep a night to function, and those who claim they can get by with even less.

Why might it be that some people need less sleep than others? The simple answer seems to be that it all lies in our genetics, and certain mutations in our genetic code are linked to a greater resistance to the effects of sleep deprivation. A particular set of gene mutations outlined by Pellegrino and colleagues (2014) was associated with a reduced need for sleep and fewer negative effects associated with reduced sleep (6 hours). They established that a reduced need for sleep, or an increased resistance to sleep loss, is heritable and the genes involved seem to impact the internal clocks we have in every one of cells.

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“Sleep is not simply an inconvenience to our daily lives but an important part of keeping us functioning.”

Yet, there is a problem with these studies, and others which have looked at those resistant to sleep deprivation. Some individuals may be resistant to effects of sleep deprivation on attention and day-to-day functioning, but most of the large sleep studies have focused on the health impacts of sub-par sleep over very long periods of time. These ‘sleep-deprivation resistant’ studies are conducted over the course of a couple of weeks; the long-term impact of sleeping less than 7-8 hours, and being resistant to short term sleep restriction, has not be extensively studied.

Therefore, it is conceivable that individuals can go with less than 7-8 hours’ sleep in the short term, and some may be better than others at getting away with this. However, ‘getting away with it’ may be just the term we want to use here. These individuals may be able to compensate early on but still be prone to the same health issues associated with reduced sleep as the rest of us in the long term.

Effect of Chronotype

I am about to go off a seemingly unrelated tangent but bear with me (it’ll be interesting, promise!) When people think and talk about sleep in terms of what is optimum and healthy, they will often focus on the duration of sleep. Most people will also mention when they drop off and wake up, but a large part of this conversation will be in relation to their willpower and how they “should really go to bed earlier and wake up earlier”. However, when we go to sleep is an important factor to keep in mind as we look at what healthy sleep looks like. Each of us can be classified on the basis of something called a chronotype and this describes at what time we go to sleep and wake up on a typical day. Although people fall along a complete spectrum, and show some variability, there are two main camps which most tend to fall into: early risers and night-owls. As the names suggest, early risers go to bed earlier and wake up earlier than the night-owls who find themselves more productive later in the day and subsequently wake up later. Great, thanks for the information Jack, but why is this important for my further understanding of healthy sleep?

Although sleep duration is important for a healthy mind and body, the time at which our body wants us to sleep and rise will impact on whether we can achieve the right amount of sleep in the first place. Our current schooling and working world favours the early-risers. As a result, night-owls unfortunately have to constrain their normal sleeping patterns during the working week to fit with the demands of a 9-5 society. This is important, as night-owls may catch-up slightly on their sleep schedules during the weekend but this is rarely enough and produces what is known as social jet-lag. This is the mismatch between what our body-clocks are screaming at us during the week when we wake up earlier than we would naturally do so, and the extended sleep we have during the weekend to attempt to rectify this.

The attempt to rectify the sleep-debt during the weekend is not enough, and this is highlighted by the increased prevalence of mental illnesses in those who score as night-owls on chronotype measures. Therefore, when as well the duration of sleep is important when we consider what healthy sleep should look like. Granted, altering the duration of sleep might be simpler to achieve for most of us than being able to get up later, but that does not make ignoring our own sleep rhythms any less important.

So, although I could likely go on for much longer, I should leave it there. The take home message is that 7-8 hours is the ideal duration of sleep required for a healthy existence. We should also be mindful that duration is not the only indicator of healthy sleep, and listening to your own sleep rhythms is important to ensure you get sufficient and good quality sleep.

Afterword

So,  I have to admit that the inspiration for this question came not from me directly. In fact, the question was part of a project which is collecting an increasingly large database of questions about science in general. The project, known as The Science Room, is run by a good friend of mine in Southampton, and it is determined to answer everyone’s science questions (ambitious, I know!) On that note, if you’re interested in asking any science based questions or learning more about the project, you can find the current webpage here: http://thearthousesouthampton.org/the-science-room/

The answer to this particular question is due to appear on a website dedicated to answering all of these questions (amongst many other things!) I shall link that site here when it’s complete.

Inquisitive Tortoise

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Header Image: Exhaustion

Second Image: Clock

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