This is the first in a three-part series What You Need to Know About Sleep. This part sets out the basics of our sleep phases, what happens to our bodies when we sleep, and how much sleep we need. Part 2 sets out the health impacts of not getting enough sleep, and in Part 3 I share my bumper list of evidence-based tips and tweaks to help you get a better night’s sleep!
Pretty much everyone knows that sleep is important. We all know that exhausted, irritable, spaced-out feeling that comes with a bad night sleep. Nothing emphasises the importance of sleep like spending a night (or more!) without it.
And yet so many of us push sleep down our list of priorities.
I think this is in part due to how busy we all are. I also think it’s because we let ourselves fall into habits (like late-night internet shopping and netflix binge-watching) that eat into our sleep. And I think too that although we all know that “sleep is important”, we don’t really truly understand how vitally important sleep is for our mental and physical health, and how devastating the effects of poor sleep can be.
The fact is, when it comes to health and wellbeing, getting enough quality sleep is right up there with good nutrition and getting enough exercise.
Stages of Sleep
Sleep is not simply an inert state of unconsciousness. A LOT goes on without us even being aware of it. We actually cycle through a number of distinct stages of sleep throughout the night. These cycles are broadly categorised into REM (Rapid Eye Movement) Sleep, and Non-REM Sleep.
REM Sleep: We cycle into REM sleep every 90 minutes to 2 hours. You can usually tell when someone is in a REM Sleep stage because you will see their eyes darting around under their eyelids. Our brain shows significant electrical activity during REM Sleep, and this is the stage where we are most likely to dream.
Non-REM Sleep: This is the name scientists give to any of our sleep that is not REM Sleep. Doesn’t give us much insight, does it? Well fortunately the American Academy of Sleep Medicine has further classified Non-REM Sleep:
N1 (Non-REM Stage 1): is the transitional, drowsy, just-dozing-off stage where you are not quite awake yet not fully asleep.
N2 (Non-REM Stage 2): is the stage where you have actually fallen asleep. Your breathing and heart rate starts to slow, and your body temperature drops.
N3 (Non-REM Stages 3) or SWS (Slow Wave Sleep): this is the slow-wave or “deep” sleep stage of your sleep cycle. Your heart rate, blood pressure and respiration are at their lowest. Scientists and sleep specialists are often very interested in this stage, as the bulk of our body’s restorative, repair and growth processes occur during deep sleep.
We cycle through all of the above stages several times each night, but as the night progresses we spend different amounts of time in different stages. Most of our deep sleep occurs during the first third of the night, whilst our periods of REM Sleep per-cycle increase as the night progresses, with our longest stretches taking place nearest to our wake-up time.
What happens to our bodies when we sleep?
Our cardiovascular, circulatory, respiratory, renal, nervous and endocrine systems are all altered during sleep. Here are some of the things your body does during sleep:
Your brain sorts, files and makes sense of all the information it takes in while you are awake. Sleep has been shown to be important for long-term memory and consolidation of learning.
Recent studies have found that our brains “clean house” while we sleep, particularly deep, slow-wave sleep.
Endocrine functions such as growth hormone, thyroid hormone, and melatonin secretion are influenced by sleep. Melatonin levels increase in the evening to make you sleepy. Growth hormone secretion typically takes place during the first few hours after sleep onset and generally occurs during deep sleep, facilitating your body’s growth and repair processes. Your cortisol (stress hormone) levels decrease throughout the night and your sympatheric (fight-or-flight) nervous system downregulates.
Your body releases anti-diuretic hormone, to reduce your urge to urinate through the night.
Your immune system releases anti-inflammatory cytokines. Studies have found a link between sleep deprivation, inflammation and immune function.
This table (from this book) details of the physiological changes our bodies undergo during REM and Non-Rem Sleep:
When it comes to sleep, we all want to know “how much sleep is enough?”. But it can be a little frustrating trying to pin down an exact hours-and-minutes answer…
The Seven Hour Rule-of Thumb versus Your Unique Sleep Needs
Epidemiological (population) studies pretty consistently indicate an association between consistently getting less than 7 hours’ sleep and an array of not-so-great health issues including obesity, cardio-vascular disease, impaired immunity and even depression. When whole populations and large groups are studied, six-to-eight (averaged to seven) hours sleep is associated with lower mortality and lower disease rates.
So it’s not surprising that organisations like the National Sleep Foundation and the American Academy of Sleep Medicine recommend we get at least 7 hours of sleep on a consistent basis.
While these guidelines provide a reasonably good rule-of thumb, all sleep experts warn that individual sleep needs will vary according to age, habits, lifestyle, genetics and environment. For example, if you have been chronically sleep deprived or are dealing with illness or injury, it is likely that you may need 9 or more hours of sleep while you recover.
Hours in bed doesn’t always equal hours asleep
This is because we all experience multiple periods of wakefulness during the night. If we are lucky, they only last minutes or seconds and we aren’t even aware of them. But it is likely that we could wake up to 20 or even 30 times a night, and the duration of our wakefulness will vary.
I’ll dig into this a little more in Part 3 of this series when I set out some evidence-based tips to improve your sleep, but for now just remember that if you are aiming for 7 hours, allow yourself about an hour of “buffer” to account for those periods during the night when you are awake.
It’s not just about the hours you put in - Sleep Quality counts too!
So what is “good quality sleep”? Last year the National Sleep Foundation analysed 227 studies and published a list of indicators of good sleep quality in its first report on sleep quality recommendations.
According to the NSF, you are getting “good quality sleep” if you:
Can fall asleep within 30 minutes of getting into bed. The lag between going to bed and actually falling asleep is called “sleep latency”.
Are asleep at least 85% of the time you are in bed (the amount of sleep:bed time is called “sleep efficiency”. If you are asleep 85% or more of the time you are in bed then you have good sleep efficiency!
Have no more than 1-4 periods of wakefulness that is longer than 5 minutes, with a heavy emphasis on one or less.
You stay asleep for more than 20 minutes after first falling asleep.
And if you want to get a little more granular about it, the National Sleep Foundation also looked at our different stages of sleep and found that “good quality” sleepers:
Are in REM sleep for 21-30% of their total sleep time.
Are in “N3” or deep, slow-wave, restorative sleep for 16-20% of their total sleep time.
If you have a sleep tracker (I use my Fitbit Alta HR* to track my sleep, along with a bunch of other things like my daily steps and hear rate) you will find it much easier to track both sleep quality and sleep versus waking duration.
So how can I tell whether I am getting enough (hours and quality) sleep?
Remember, our individual sleep needs will vary according to age, habits, lifestyle, genetics and environment.
First, look at your hours in bed. A good first step is to look at how many hours you are actually in bed. If it is less than 7 hours per night, then you may be at risk of not getting enough sleep for your needs.
In addition to sleep hours, assess your sleep quality.** If you have a sleep tracker, it should be able to give you at least a rough indication of your periods of wakefulness throughout the night, as well as REM and Deep Sleep.
But the most important indicator of your sleep quality is how you feel upon waking and throughout the day. If you don’t feel rested and refreshed when you wake up in the morning, if you feel tired or fatigued throughout the day, feel moody, have difficulty with concentration or recall, then chances are pretty high that you aren’t getting enough sleep, or enough quality sleep.*** And it’s likely that you will benefit from taking some simple steps to improve your sleep habits.
When I work with a coaching clients to improve their sleep, we first work on making sure they form a few good habits to make sure they are actually putting in the hours they need to get a good night’s sleep. And once we have embedded a great sleep schedule, we then focus on doing what we can to improve sleep quality too.
I will be sharing a bumper list of evidence-based tips to help you improve your sleep in Part 3 of this series (so subscribe to my newsletter to make sure it lands in your inbox).
Altevogt BM, Colten HR, editors. Sleep disorders and sleep deprivation: an unmet public health problem. National Academies Press; 2006.
NHLBI (National Heart, Lung, and Blood Institute). Sleep, Sleep Disorders, and Biological Rhythms: NIH Curriculum Supplement Series, Grades 9-12. Colorado Springs, CO: Biological Sciences Curriculum Study; 2003.
Badr MS, Belenky G, Bliwise DL, Buxton OM, Buysse D, Dinges DF, Gangwisch J, Grandner MA, Kushida C, Malhotra RK, Martin JL. Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine. 2015 Jun 15;11(06):591-2.
Consensus Conference Panel (2015). Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine, vol.11, pp. 591–592.
Hirshkowitz M, Whiton K, Albert SM, Alessi C, Bruni O, DonCarlos L, Hazen N, Herman J, Katz ES, Kheirandish-Gozal L, Neubauer DN. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health. 2015 Mar 1;1(1):40-3.
Watson NF, Badr MS, Belenky G, Bliwise DL, Buxton OM, Buysse D, Dinges DF, Gangwisch J, Grandner MA, Kushida C, Malhotra RK, Martin JL, Patel SR, Quan SF, Tasali E. Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society on the Recommended Amount of Sleep for a Healthy Adult: Methodology and Discussion. J Clin Sleep Med 2015; 11: 931-952
Ohayon M, Wickwire EM, Hirshkowitz M, Albert SM, Avidan A, Daly FJ, Dauvilliers Y, Ferri R, Fung C, Gozal D, Hazen N. National Sleep Foundation's sleep quality recommendations: first report. Sleep Health. 2017 Feb 1;3(1):6-19.
Ojile J. National Sleep Foundation sets the standard for sleep as a vital sign of health. Sleep Health: Journal of the National Sleep Foundation. 2017 Aug 1;3(4):226.
* I have no relationship with FitBit. I’m just mentioning what I’m currently using to track my sleep in case you are curious. If you use a sleep tracker and are really happy with it, drop me a line and let me know!
** The most accurate way of assessing your sleep quality is to have a sleep study done. This will be discussed further in Part 3.
*** Tiredness, fatigue and concentration deficits can also be a sign of nutritional deficiencies or other medical issues, so I HIGHLY (HIGHLY!!!!!) recommend you check in with your family doctor to let them know how you are feeling so they can rule out serious illness or a nutritional deficiency like iron or B12 while you work on improving your sleep!