Category Archives: PhD

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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Filed under PhD, Psychology, Sleep Science, Uncategorized, Work and Society

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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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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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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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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Sleep Snippet: Why Bother Even Trying to Understand Sleep?

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Sleep in its natural environment.

It’s a fair question (although don’t tell my supervisors that I said that…) We enjoy doing it, it refreshes us, and we tend to find ourselves doing it in any spot we find ourselves last thing on a Wednesday afternoon. Most of us could identify that we need sleep and that it helps maintain the brain and body in some way but why do we need to go any further than that, other than for pure curiosity?

Sleep is important for our ability to function in the world about us. As we are likely all aware, a night without sleep or a few days with very little sleep can make it incredibly hard to do much of anything. We find it hard to concentrate on conversations with colleagues or friends, find ourselves becoming more forgetful and start to see every nook and cranny as ideal spots for a quick nap. In addition, we become more irritable and may find it harder in general to control our emotions. If we have been deprived of sleep for long enough, we may even start to see and hear things which are not really there and become increasingly paranoid.

For most of us these experiences are temporary and we can largely shrug off the negative effects of too little sleep by making sure we go back to a regular routine of sufficient sleep. However, what about those who can’t? What about people who struggle to sleep at all and who do not feel rested after a night in bed? It is important to understand a) why these individuals struggle with sleep and b) how poor sleep leads them to experience the negative side-effects we all do but to a much greater degree? The second question, in part, can be understood by trying to explore the effect of a lack of sleep on relatively healthy individuals like you and me.

The importance in understanding why we sleep and how this should look in the brain lies in how we can use that knowledge to help those who can’t sleep or whose sleep is disturbed significantly. This can involve those who suffer from sleep disorders such as insomnia (where we don’t sleep enough), hypersomnia (where we sleep too much), and narcolepsy (where we unexpectedly fall asleep throughout the day) to name a few examples.

We can also look at the role of sleep difficulties in the context of other illnesses, where problems drifting off to sleep and staying so can exacerbate or lead to many different symptoms of disease. For example, sleep difficulties have been implicated in many mental illnesses such as schizophrenia, depression and anxiety disorders. In fact, around 80% of individuals with schizophrenia will experience some form of sleep disruption. Sleep difficulties have also been shown to have an influence on diseases of the immune system such as ulcerative colitis, psoriasis, and in neurological conditions such as Parkinson’s disease. I am very conscious of how many different disorders I could list where an understanding of sleep could help to reduce suffering but that might make for a rather boring article (and not help with my self-imposed word limit…) Through understanding sleep, we can understand these related illnesses to a greater extent and hopefully provide better treatments for patients.

Hopefully, in this short snippet of an article has shown that understanding why and how we sleep is important and worthwhile.

Inquisitive Tortoise

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The Creature at the End of the Bed: What is Sleep Paralysis?

Sleep Paralysis

A fitting depiction of the sleep paralysis experience for many.

My limbs won’t move. I can’t scan the room or, more importantly, run if I needed to. This feeling in itself is terrifying, but I become aware of an evil presence in the room. It’s behind me and is waiting there. All I’m aware of is a jagged shadow which means me some ill. I’m desperate to move, to escape, to scream out and run from this figure watching me. Minutes pass and my focus is on moving, willing my failing limbs to spring into action. Suddenly they return back to life and I instinctively look towards the corner of the room where I felt a malevolent being was sizing me up. There’s nothing there but darkness and my old blue wooden wardrobe. Shaken and tired, I attempt to drift back to sleep and forget that the shadow could still be out there.

My first, and only, experience with sleep paralysis occurred when I was about 6 years old and coincided with my sleep-walking phase. It was a brief but terrifying experience and although I don’t remember it perfectly, the feeling of vulnerability and that shadow’s presence remain with me.  The experience of sleep paralysis differs from person to person but there are constants to everyone’s experience. There is the characteristic paralysis of voluntary muscles and often, but not always, this is accompanied by hallucinations which can leave the person frightened and disoriented. The hallucinations experienced by sufferers of sleep paralysis also appear deeply embedded in different cultures, literature and history (see sleep paralysis as a cultural phenomenon below).

These hallucinations can be grouped into intruder, incubus and vestibular hallucinations. The intruder hallucination, whereby there is a feeling that there is a being in the room with you, with the feeling of malevolent intent is the type I experienced as a young child. However, experiences of a great weight on your chest attributed to a demon-like creature and the feeling of floating can be identified as incubus and vestibular hallucinations respectively. These experiences are particularly distressing for those who are unfamiliar with their cause and has led some to wrongly believe they were suffering from psychosis.

Although a bizarre experience, it is not all that uncommon. A large systematic review (a comprehensive report which gathers all of the studies, in theory, ever conducted on a topic) of the prevalence of sleep paralysis found that “7.6% of the general population, 28.3% of the student population, and 31.9% of psychiatric patients experienced at least one episode of sleep paralysis” (Sharpless & Barber, 2011). It’s interesting to note that it should be so prevalent amongst student populations.

So, what is at the root of sleep paralysis episodes? It appears that sleep paralysis is linked to REM sleep and the transition to and from this stage of the sleep cycle. Interestingly, in a sleep disorder known as narcolepsy, characterised by sudden onsets of sleep, the prevalence of sleep paralysis is around 50%. This is considerably higher than the normal population, and it might be due to the sudden onset of REM sleep seen in individuals with narcolepsy. Moreover, narcolepsy is also associated with partial sleep paralysis. This is where there is some limited movement available to the individual but they are likely paralysed and experience the powerful and frightening hallucinations seen in sleep paralysis.

In my last article, I talked about how it is possible to induce sleepwalking in those with a genetic risk by sleep depriving them. It appears that the same trick can be useful in eliciting sleep paralysis episodes in students. A study by Takeuchi and colleagues (1992) showed that by waking students up at just the right time they were able to elicit sleep paralysis in their sample. More specifically, by waking up participants when they were just about to enter REM, they were able to manipulate it so that participants were more likely to go directly into REM sleep as they drifted off again. However, this technique is far from perfect in eliciting sleep paralysis as out of 64 successful REM interruptions, only 6 episodes of sleep paralysis were recorded in 5 out of 16 participants. This suggests that sleep onset REM is involved in sleep paralysis but there are likely other factors which play a role here. For example, stress and physical tiredness (beyond being woken up in a sleep laboratory) may also contribute to the likeliness of sleep paralysis occurring. This may explain why student and psychiatric populations are more prone to sleep paralysis episodes.

As I have already, hopefully, addressed with sleepwalking, there is a clear and long history of sleep paralysis as recorded in literature and historical medical reports. We have identified the different subtypes, linked it to a particular stage of sleep and started to identify some connections with other sleep disorders (e.g. narcolepsy). However, this is largely where our understanding of the phenomenon ends. It appears that problems in the REM stage of sleep are important in the production of sleep paralysis but more work is needed to understand what these are and why they are important.

Sleep Paralysis as a Cultural Phenomenon

S5765870281_a51d288e54_zleep paralysis occurs across a wide range of different cultures and there is historical evidence of it occurring throughout the history of medicine and literature. Folk terms such as the “old hag”, the “Pandafeche”, and visitations by demonic presences such as succubi and incubi have been attributed to sleep paralysis.
Many of these lay blame for experiences on paranormal or spiritual beings, with a focus on witch or ghost-like beings (old hag and pandafeche), and given the content of hallucinations experienced alongside sleep paralysis this is not surprising.

The painting, ‘The Nightmare’ by Henry Fuseli is commonly believed to be a depiction of sleep paralysis and a case study from the 1600s exists which describes sleep paralysis in vivid detail (Kompanje, 2008). Interestingly, the previous case study also highlighted how body position while sleeping might contribute to sleep paralysis and hallucinations experienced with it. There is some recent evidence which suggests that lying in a supine position (on your back, face up) may be associated with increased rates of sleep paralysis and associated hallucinations. The 17th century case study provided the earliest evidence of this facet of sleep paralysis.

Inquisitive Tortoise

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