SciBlogs

Spring forward, fall back: Daylight savings transition Karyn O'Keeffe Mar 30

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Whenever there is a pending change to or from Daylight Savings Time (DST), there is often discussion about the effects this will have on our sleep.  It is fair to say that there is generally less concern with the transition we are about to experience (from DST to Standard Time).  Most people simply don’t worry about it and look forward to an extra hour of sleep. 

Fewer adverse outcomes arise from the transition from DST, than the transition to DST*.  That said, changes in sleep and performance are still experienced.  These fall into two categories: (a) the changes we experience from the shift in the day/night cycle compared to the timing of our own internal body clock, and (b) the effects of our behavioural responses to transitions to and from DST.  This Sunday’s change from DST to Standard Time requires our body clock to shift an hour later**.  This shift is an easier one; our clock likes to drift later anyway.  However, the gradual seasonal changes we experience in the day/night cycle also help this along. 

Winter is a time of short daylight hours and long nights.  As we head out of winter, our daylight hours lengthen.  They extend at both ends of the day, which means to make full use of our daylight hours we would have to be up at 4-5am (simply not sensible for optimal daytime performance).  DST provides a way of shifting our daylight hours to be one hour later.  This transition means we shift our day/night cycle one hour forward in relation to our internal body clock.

Conversely, as we head out of summer and into winter, the days become shorter.  Suddenly, our change to a later day/night cycle means there is less light in the morning, so we opt to shift from DST back to Standard Time.  This gradual shortening of daylight hours, and the drift to a later sunrise, will lend a helping hand in coping with this Sunday’s DST transition.  Those of you who are lucky enough to wake without an alarm clock may have noticed that you have already begun to wake later.  Daylight hours have a profound effect on the timing of our internal body clock and consequently, our sleep.

The change from DST to Standard Time provides an opportunity to catch up on an hour’s sleep.  However, only those who are missing out on sleep will be able to sleep in***.  Catching up on sleep might have a positive effect by reducing sleepiness, and improving your cognitive and motor functioning.  For those of us who don’t want to sleep in, we will need to be aware that we will have a longer waking day than usual (approx. 1-hour longer).  Towards the end of our day, we will become sleepier, our performance will start to decrease and our risk of accidents will increase.

It is thought that behavioural changes may play a large role in the risk of sleepiness (and therefore, accidents) during DST change.  A transition from DST may mean that individuals who usually stay out late on Saturday nights choose to stay out even later.  Individuals may also stay out later on several nights preceding DST change in the knowledge that they will be able to catch up at the weekend.  Another consideration with Sunday’s DST change is the extra hour that needs to be fitted into the work schedule of shift workers.  Extended hours of work may also lead to sleepiness, and increase the risk of accident or injury.  If you have been up for longer than usual, or later than usual, make sure it is safe for you to drive home.

 

* I will save discussion about the change to DST for later in the year

** Give or take, depending on your recent sleep routine.  Additionally, our endogenous clock time is not 24-hours.

*** A good proportion of us are able to sleep in during DST change, what does this tell us about our sleep habits?

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The (supposed) myth of the 8-hour sleep Karyn O'Keeffe Mar 12

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Last week a sleep colleague and I gave a presentation to a group of GPs.  It was one of those slightly disorganised things where you know what you’re presenting but not a great deal about anyone else’s presentation.  Our introduction by a GP colleague of ours gave a light-hearted overview of the importance of sleep… including a recent discovery that our belief that we need 8 hours sleep was a myth.  I felt slightly panicked at this suggestion.  In most part because I couldn’t believe I had missed a news story this big.  Had I really not been paying attention to my RSS feeds that week?  However, after a quick search, this is what I found:

BBC News Magazine: The myth of the eight-hour sleep **

Reading this title, what’s your first thought?  That we don’t need 8-hours sleep, right?  Hands up anyone who thought ‘I knew that I could get away with 6’?

But in fact, this is not what the BBC article reports.  It discusses the concept of biphasic sleep – sleeping in two, approximately 4-hour chunks across the night.  This concept is not a new one.  As the article points out, there are many historical reports of individuals waking for a couple of hours in the middle of the night.  In general, these hours were whiled away with activities such as reading, writing, chatting or intimate relations.  Note, there were no electrical light, TVs or tablets in these historical times.  Bed time was a lot earlier than ours, and the time available for sleep from bed time to final wake time was a lot longer.

I am not particularly knowledgeable of the historical accounts of this phenomenon but it has been studied scientifically.  In the early 1990s, Thomas Wehr investigated the effect of changing the length of daytime light exposure (and conversely, night length) on sleep, and found that with long nights, human sleep occurs in bouts, with periods of quiet wakefulness during the night.  Wehr hypothesised that it was our modern sleep/wake pattern, with considerably and chronically shortened sleep periods, that increased sleep propensity and drove consolidated sleep.  When Wehr gave people a 14-hour sleep opportunity, they had a few days of catch-up sleep (11-hours in total!) followed by sleep in two main bouts, with a period of quiet wakefulness in between.  Each bout lasted about 2-5 hours with the wakefulness period lasting 1-3 hours.  How long did these people sleep in total?  8.25 hours on average.

 

 

** If you didn’t think that one was misleading, have a look at this.  I suppose, an exercise in what happens if you rip off another’s news article without reading any of the background material.

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Chill out with melatonin-laced brownies? Karyn O'Keeffe May 18

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To the casual observer, it may appear that some months ago I started to blog on sleep, wrote a few posts… and then simply disappeared from the blogosphere.  Unfortunately, April was a month of over-commitment on my part (I’m really good at that).  But, I’m back…

During the last few days, my Google reader has been filled with reports of a controversial new brownie (“Lazy Cakes”) available for sale in the United States.  This latest edition adds to a range of baked goods and/or dietary supplements aimed to promote relaxation and therefore supposedly, sleep.

Sold at supermarkets, and department and convenience stores, Lazy Cakes contain ingredients the manufacturers believe promote relaxation, such as valerian root, rose hips and melatonin.  Although not explicitly cited on the Lazy Cakes website, web commentary has suggested that these products may be used to promote sleep.  Certainly, a New York Times article cites individuals with insomnia who have tried Lazy Cakes.  Much of the web discussion at present has centred on the use of melatonin in these brownies and in particularly, the reasonably high dose of 8mg melatonin per brownie.

There is considerable concern about taking melatonin as a dietary supplement.  Melatonin is a neurohormone that interacts with a number of systems in the body, of which only one is the circadian (body clock) system.  It also has a significant role in the control of our reproductive function, thermoregulation, thyroid function, carbohydrate and lipid metabolism, urine output, immune function… the list goes on.

Many people associate melatonin with a sleep-promoting hormone because it is secreted at night (coincidentally when humans sleep) and suppressed by light during the day.  In fact, melatonin is secreted at night regardless of whether we are diurnal (active during the day) or nocturnal (active at night).  When it comes to sleep/wake information, melatonin’s main role is to tell us what time of day it is.  Melatonin also changes seasonally in all mammals (including humans) so it can also tell mammals what time of year it is, which is important for reproduction and hibernation.

Many studies have considered the influence of melatonin on our sleep timing and quality.  In humans;

  • Melatonin’s main action is in its ability to shift the timing of our sleep by changing the timing of our body clock.  This means that taken at the wrong time of the day, melatonin may shift the timing of your sleep to an undesirable time.  Timing instructions do not come on the packets/bottles of melatonin-containing products.  Would you know exactly when you should be administering melatonin to optimise your sleep timing?
  • Melatonin has no effect on sleep quantity or quality when used as a sleep aid.
  • Timed appropriately, melatonin can shorten the time it takes you to fall asleep but in healthy adults, this effect is usually incredibly small (something like 4 minutes on average; statistically significant but not clinically significant).  It does seem to be more effective at reducing the time it takes to fall asleep in those with insomnia, but it still does not change sleep quantity or quality in this group.
  • Acute side effects include, commonly, headache and taken during the active day, sleepiness and fatigue.
  • We do not know the long-term risks associated with frequent administration or inappropriate timing of melatonin.  At present, the greatest concern lies with its effect on our reproductive function, including reproductive cancers.

To the general public, melatonin is usually promoted as a product for those who are having trouble sleeping, including those with insomnia.  As someone who is not an advocate for pharmacologic treatment for chronic insomnia, if it were me, would I regularly take dietary supplements containing melatonin to improve my sleep?  Not on your life.

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Measuring sleep: The squiggles explained! (Part 2) Karyn O'Keeffe Apr 07

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In a previous post, I provided an overview of the stages of human sleep.  But how do we determine what stage of sleep a person is in?

The current gold standard for objectively measuring sleep is called polysomnography or PSG. This mouthful is derived from the Greek poly meaning ‘many’, somnus meaning ‘sleep’ and graphein meaning ‘to write’.  Polysomnography allows us to record a wide range of physiologic signals during a sleep period.  At the simplest level, we will record signals that allow us to stage human sleep, but in addition we often measure signals such as heart rate, breathing (effort and airflow), muscle movement, oxygen saturation, carbon dioxide levels and behaviour (via video input).  Each recorded signal requires a sensor, or several sensors, often making this quite an overwhelming experience for a patient or research participant.

To be able to determine the stage of human sleep, we need to simultaneously measure three particular signals; electroencephalogram (EEG; brain waves), electrooculogram (EOG; eye movements) and electromyogram (EMG; chin muscle tone).  These measurements are taken via Grass gold cup electrodes (although silver chloride may also be used) filled with a conductive paste or gel. To be able to accurately stage sleep, each electrode needs to be placed at a particular site. For example, the EEG is applied according to the International 10-20 electrode placement system.  After the recording is completed, a trained Sleep Physiologist (also known as a Sleep Technologist or Sleep Scientist) visually examines each 30 second epoch of the EEG, EOG, EMG signals, and applies a sleep stage following international rules for sleep staging [1, 2].  This is an incredibly time consuming process that requires a reasonable level of skill.  Unfortunately, no computer can yet accurately see what a Physiologist can with their own eyes.

There are advantages and disadvantages to quantifying sleep in this way.  The discussion is too big for this post but in essence, sleep has been measured this way for most of its (fairly) short existence as a science.  Continuing to do so allows us to put any new research in context.  However, applying static sleep stages in this manner does not take into account the continuous nature of sleep and in addition, brief changes in sleep status are lost with our current method.  Many researchers are now looking at additional ways of analysing brain activity during sleep and I hope to share some of these with you in later posts.

References

  1. Iber, C., Ancoli-Israel, S., Chesson, A., & Quan, S. F. (Eds.). (2007). The AASM manual for the scoring of sleep and associated events: Rules, terminology and technical specifications (1st ed.). Westchester, IL: American Academy of Sleep Medicine.
  2. Rechtschaffen, A., & Kales, A. (Eds.). (1968). A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects. Los Angeles, CA: Brain Information Service/Brain Research Institute, University of California.
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Measuring sleep: The squiggles explained! (Part 1) Karyn O'Keeffe Mar 23

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I’m sure you’ve been wondering all week about the strange ‘squiggles’ in my blog banner.  Well, perhaps not, but the sleep geek in me hopes that at least one of you has.  My blog banner has a segment of an electroencephalogram (EEG) or ‘brain waves’.  This is a recording of my EEG, in fact. At this point in the night, I am in Stage 2 sleep.  Each night when we go to sleep, we will experience non-REM sleep and REM sleep.  Non-REM sleep (also written as NREM sleep) has been further categorised as Stages 1 through 4. 

A bit of sleep history… The concept of sleep stages was first postulated in 1937 by Loomis et al.  This concept went through several iterations in the following decades.  However, it was Aserinky and Kleitman’s groundbreaking discovery of REM sleep in the early 1950s that set us on the path to defining sleep as NREM sleep and REM sleep.  Sleep stages as we currently know them were defined by a committee of sleep researchers, chaired by Allan Rechtschaffen and Anthony Kales in 1968. These criteria have recently been updated by an American Academy of Sleep Medicine committee (2007) to comply with our current understanding of sleep physiology.

Most of us have an understanding that we go through each of the different sleep stages each night but few of us know what our sleep actually looks like.  The answer is complicated as our sleep structure is different on every night, but sleep structure does follow a general pattern.  Let me show you…

The diagram above shows a schematic hypnogram1 of sleep stages across the sleep period.  A hypnogram is a graphical way of presenting changes in sleep structure.  On the y-axis you will be able to see Stages 1 through 4 sleep and REM sleep.  Stage 1 is the lightest stage of sleep and comprises up to 5% of the sleep period.  Stages 3 and 4 are the deepest stages of sleep.  These are collectively referred to as slow wave sleep2, denoting the slow frequency, high amplitude EEG seen during these stages.  Our threshold for arousal is highest during slow wave sleep therefore this stage is also referred to as deep sleep.  Slow wave sleep and REM sleep each comprise approximately 20% of the sleep period in a healthy young adult.  The remainder of our sleep period is made up of Stage 2 sleep, or ‘light’ sleep.

The hypnogram also depicts changes in sleep that occur across the sleep period.  Slow wave sleep predominates in the first half of the night and REM sleep in the latter half.  Transition through all the sleep stages are reasonably cyclical and repeat every 90 minutes, approximately.

Does sleep really look like the schematic version of the hypnogram?  Sort of…

The hypnogram above is an example of real sleep in a healthy young adult.  Notice the trends are similar – more slow wave sleep at the beginning of the night and more REM sleep in the latter half of the night.  However, I’m sure you’ve noticed that this individual chops and changes between sleep stages all the time.  This is not unique; you and I would do this each night as well.  The activity in the brain is changing frequently during sleep and this is reflected in our frequently changing sleep stages. 
 

These rapid changes in brain activity also mean it is also quite normal for the brain to return to wakefulness on a frequent basis.  Arousals from sleep are shown in the lowest panel in the hypnogram.  One vertical line represents one brief arousal from sleep.  Arousals are an expected part of normal healthy sleep; in a healthy young adult these arousals typically occur 10-15 times per hour of sleep.  We are not aware of any of these brief arousals as they usually only last a matter of seconds.

No doubt this post has left you with many questions.  I can imagine a few…

Does our sleep change with age?  Yes.  Is there such a thing as ‘too many arousals’?  Yes.  Why is there a difference between the number of arousals and the indication of Wake on the hypnogram?  We’ll have to leave the detailed answers to these questions for another time.  If you have questions, let me know in the comments section and I’ll do my best to address them in future posts.

 

1 Hypnogram kindly reproduced with permission from Gander, P. H. (2003). Sleep in the 24-hour society. Lower Hutt, New Zealand: Open Polytechnic of New Zealand.

2 The 2007 sleep staging criteria refer to slow wave sleep collectively.  That is, Stages 3 and 4 sleep are no longer defined separately.

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Caffeine affects your sleep. No ifs, no buts. Karyn O'Keeffe Mar 11

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Caffeine is one of the most commonly consumed psychoactive substances.  It is everywhere, in coffee, black tea, green tea, soft drinks, energy drinks, chocolate and over-the-counter medications.  We are all aware that caffeine is a stimulant; however, few of us appreciate that caffeine can have a significant impact on our sleep.

Do any of these statements ring a bell?

Myth: Coffee has no effect on me.  I can have a coffee right before bed and have no problem going to sleep.

Fact: If you ingest enough caffeine you may have trouble getting off to sleep but in a regular caffeine consumer this is not usually where the damage is done.  Caffeine adversely affects the quality of your sleep.

Myth: I don’t drink much caffeine.  I drink tea.

Fact: Brewed products are the most variable in caffeine content, and caffeine is found in both coffee and tea, including black and green leaf.  To put caffeine content in perspective, the average cup of coffee contains 100mg of caffeine whereas a regular latté from a coffee shop like Starbucks contains approximately 250mg, maybe more.  A cup of tea contains caffeine in the range of 40-70mg and a can of cola, about 40mg.

There are a number of processes that control how and when we sleep.  One of these processes is called the sleep homeostat, which refers to our ‘need for sleep’.  In simple terms, the longer we are awake, the more we need to sleep.  This process is, in part, mediated via an inhibitory neurotransmitter called adenosine, which reduces neuronal firing rate and inhibits the release of neurotransmitters that are involved in wakefulness and arousal.  Adenosine makes us sleepy.

Caffeine is an adenosine antagonist; it blocks adenosine receptors by inserting itself instead.  It enters our system reasonably quickly and is at peak plasma levels in 30-75 minutes.  During the day, caffeine gives us a quick boost in alertness, and may improve attention and reaction time.

The problems arise with processing caffeine.  The half-life of a single dose of caffeine is 3-7 hours.  The more caffeine we put in our system, the longer it takes us to get rid of it.  Caffeine predominantly breaks down to paraxanthine, which is has similar biological properties to caffeine and also acts to reduce clearance of caffeine.  Unfortunately, the more caffeine we ingest, the more paraxanthine we produce leading to an accumulation of caffeine.  Depending on how much caffeine you are consuming and your current medical status, the half-life of caffeine can increase to anything from 11-96 hours.  Days!

So what happens when we sleep with caffeine on board?  Caffeine will cause you to have a reduced total sleep time, have less deep (slow wave) sleep and provided you’re not sleep deprived, an increased sleep latency (time to get to sleep).  Caffeine intake and poor sleep is a cycle easily repeated… you drink too much coffee today and you don’t sleep well tonight.  You wake up tomorrow morning and feel worse for wear.  Having no idea why you reach for another cup of coffee.  Sure, you fall asleep quickly each night but are you sure that it isn’t because you’ve been ruining your sleep with a steady intake of caffeine?

How much coffee should you drink?  300-400 mg is the recommended daily dose of caffeine, preferably taken before your dinner meal.  “No cup of tea before bed?!” you ask.  Sadly no, try hot lemon drinks, milo (which has a very low caffeine content), or decaf versions of tea and coffee.

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Why blog about sleep? Karyn O'Keeffe Mar 09

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Brigid Gallagher’s recent blog post on a typical conversation at a social function had me smiling.  I’m no archaeologist.  In fact, the little I know about archaeology, I’ve probably gleaned from Indiana Jones (gasp!).  Yet, there seemed to be so many parallels to the conversations Brigid has experienced and my own, that I couldn’t help but feel like we were on completely the same page.  Perhaps I’ve misrepresented Brigid here, but my conversations have also had a quiet undertone of “Seriously, you waste time every day studying that?”

Until recently, I spent a good proportion of my working week as a Clinical Sleep Physiologist, a fancy way of saying that I worked in a clinical sleep laboratory diagnosing and treating those with sleep disorders.  Most people are fascinated by this.  Questions pour out about sleep and sleep disorders.  I’m grilled on how to sleep best… and usually, am asked to interpret a few dreams.  I never tire of this.  I am fascinated by sleep and will talk about it endlessly.  Because, though many of us consider ourselves ‘experts’ (we all sleep after all), most know very little about sleep.  Thus, I am a big advocate of accurate, public information on sleep science.

Yes, science… because that’s where I usually come up against a wall.  Many people don’t associate sleep with active processes, and certainly not science.  That old mentality of sleep being a passive process akin to death often reigns supreme.  So after I’ve got through discussing how to improve people’s sleep, I find myself kindly explaining that no, I don’t just passively watch people sleep all day, take subjective ratings about sleep quality and then guess what to do next.

Sleep lags behind other medical fields.  Most of what we currently know about sleep we have learnt in the last 25 years.  This means that the importance of sleep is often trivialised.  And the public is fed an overabundance of misinformation about sleep every day.

Still there is hope.  People are generally fascinated that I can measure sleep.  Fascinated that it can be interpreted.  That sleep has functions.  Even more fascinated that it is vital for functioning and good health.  Fascinating for me is that people will listen to me blather on about sleep for hours.  And this last part gives me hope.

So I’m going to keep talking about sleep.  To everyone I can.  Quietly determined to get sleep on everyone’s health and safety radar.

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