By Dave Emond
Sleep; so simple in theory - just do it, and you’ll be fine. I really wish it were this simple, but unfortunately we are not simple creatures. As a result, there are plenty of barriers to getting good quantity and quality of sleep.
This is not an article that will address sleep pathologies. You should talk to your doctor about those. This is a general overview of the purpose of sleep, recommendations on how much sleep might be best for you, how it can positively or negatively affect day to day function and how you can try to improve it.
What is sleep, and why do we need it?
Short answer: we still aren’t sure. After years of research, we’ve come to the conclusion that sleep is extremely complex and has a wide variety of benefits and functions. Great, eh? Not only are there a wide variety of functions, these functions are often tied to different stages of sleep (1). So before we begin, here is a quick crash course on sleep and its stages:
There are two main classifications of sleep - we have Rapid Eye Movement (REM) sleep, and non-REM sleep. Within non-REM sleep there are 3 stages. These 3 stages make up the majority of your sleep, in most cases.
Stages 1 and 2 are lighter and are involved in the transition between wakefulness and deeper, refreshing sleep. Stage 3 is a stage of deep sleep, and is important when it comes to the “restorative” properties of sleep. REM sleep is a very active stage (when dreams occur), and is suggested to play an important role in the consolidation of memories and learning (2).
The many functions of sleep
So as we mentioned earlier, sleep has many suggested functions, with physical restoration being one of them. A recent theory by Schmidt, known as the Energy Allocation Model of Sleep, suggests that sleep is used to decrease the total amount of daily energy expenditure, so that energy can be used to help with the body’s essential processes, instead of activities associated with being awake, such as movement (3). The function of "restoration" falls in line with patterns of hormonal release during sleep. Most of these hormones are “anabolic” in nature - which means they help build things up (4). The release of these major hormones tends to occur during stage 3 sleep, so a light 20 minute nap likely won’t help you here (4).
Another consideration to be had for the physical restoration and energy balance properties of sleep, is that appetite regulation can be affected by sleep. Sleep deprivation is associated with reductions in leptin (a hormone that reduces hunger), and elevations in ghrelin (a hormone that drives hunger) thus resulting in greater hunger pangs (5). This does not guarantee weight gain, as caloric balance will determine this, however it does act as a driver to WANT more food and calories. What does this mean for you? It’s going to be a whole lot harder to resist those tasty snacks if you are sleep deprived.
Sleep is needed for learning and memory consolidation. This tends to occur most in deep sleep (stage 3) and during REM sleep (2). A study by Walker et al. showed sleep improves motor learning, even when controlling for confounding variables (6). The improvements in motor learning tend to be maximized with stage 2 sleep, which means you can potentially have positive effects on learning or practicing new motor skills by just taking a short nap (7).
It should be noted that when sleep time is restricted, there tends to be a protective mechanism that reduces stages 1 and 2 of sleep to favour stage 3 and REM sleep. This is thought to allow for maintenance of higher-level cognitive function (8). This isn’t to say memory and cognition cannot be affected, though. Sleep deprivation will not only affect memory, but can also play a role in promotion of perceived distress, in turn, affecting mood. Positive and neutral memory encoding is negatively affected, however negative memory encoding tends to be unaffected by sleep loss (9). In layman's terms: it is tough to remember things that are positive or neutral, but easy to remember and dwell on negative things. Yes, this one blew my mind too when I was reading the paper, but let’s be honest, we’ve all been negative and cranky when we’ve been short-changed by the sandman.
Lastly, another important function of sleep is the clearance of a variety of waste products from the brain via the "glymphatic system". This includes beta-amyloid and tau proteins which are associated with Alzheimer's disease (10). Nedergaard and colleagues have suggested that these proteins and waste products are cleared from the brain at an increased rate when asleep, than when awake (10).
I could keep going, but I don’t want you to fall asleep on me… or do I? Look at how important sleep is! Before we move on with sleep interventions, lets rehash the variety of risks associated with poor sleep in a more digestible format (1, 11):
Poor hunger regulation
Increased production of inflammatory molecules
Hypertension
Heart attack
Obesity
Diabetes
Stroke
Changes in hormonal profiles
Impaired learning
Impaired memory consolidation
Changes in mood
Increases in perceived distress
Increased risk of all-cause mortality, and many, many more
If the long list of negative health outcomes didn’t get you, surely the last point did.
How much sleep do I need?
Ladies and gentlemen, I present to you the general recommendations by the National Sleep Foundation, so you can see where you lie (pun intended). These recommendations are classified by age, and offer recommended ranges, ranges for certain outliers, and insufficient or excessive quantities of sleep (12).
As we can see, the recommended quantity of sleep changes with age. It is also important to note that the sleep dosage that “may be appropriate” is likely not appropriate for the majority of individuals within their age groups, but instead are sufficient for some outliers.
What about that sleep hygiene stuff all the cool kids are talking about?
I’m sure we’ve all heard the term “sleep hygiene”. This includes performing habits or factors that are thought to promote a better sleep experience. These are accessible, but perhaps difficult behaviour changes, such as reducing the intake of stimulants like caffeine, nicotine, or alcohol prior to bed (13), reducing blue light exposure (14) or reducing noise (15). These are all fine and dandy, but the jury is still out on how effective some of these might be at improving sleep quality (15). You can give them a go, but if they don’t dramatically change your sleep experience, there are probably lower hanging fruits to pick from.
A great starting point to improve your sleep is to arrange a consistent schedule that aligns with your period of sleepiness (this is when you should try to get to bed, instead of powering through), and period of wakefulness in the morning (this is when you should try to get out of bed, instead of going back to sleep). These can be different for everyone, so take some time to figure them out (16). Consistent sleep behaviour, although difficult for some, is key here.
Improving sleep debt
You may think - "I can catch up on sleep loss, I’ll just sleep in on the weekends". This may help in some instances, but it really does not compensate for chronic sleep deprivation in most individuals - usually only 1 in 4 people are able to compensate with catch-up sleep or naps (17). Sleep banking has also been suggested to help (increasing sleep time for a few consecutive days before an anticipated period of sleep loss). This will not prevent poor outcomes in cognitive abilities, however these individuals tend to perform better cognitively when compared to those who do not bank sleep (18). Moreover, those who were proactive will be better off when compared to those who did not bank sleep, when given the opportunity to have 5 nights of catch-up sleep (18).
Can you compensate? Sure, but only for a brief period of time before the effects of chronic sleep deprivation catch up to you. Perhaps it is wise to avoid becoming reliant on a consistent schedule of sleep banking or weekend catch-up sleep, unless your job demands it. Socio-economic factors in health are a whole other [very important] story we won’t be diving into today.
So to summarize, here are some options if you think you may not be getting the most out of your night time hours:
Try to normalize your sleep schedule to your circadian rhythm, and stay consistent with this over a long period of time (it takes time to catch up on sleep debt).
Try your best to stay within the margins of your recommended sleep dosage.
Consider modifying factors involved with sleep hygiene, but don’t view these as a panacea for improved sleep.
If you have dealt with an acute bout of sleep deprivation, catching up on sleep, or better yet, proactive sleep banking may be of benefit, but likely not for chronic sleep deprivation.
Just like any behaviour change, making changes to your sleeping habits can be a difficult process, so don’t get overly discouraged.
If you’ve been dealing with persisting sleep issues, go see your doctor who might be able to guide you or help treat any underlying pathologies (insomnia, sleep apnea, etc.).
I will also leave a few other resources to learn more on this topic. The bright folks over at Barbell Medicine have a great discussion with Dr. Nate Gordon which can be heard here. The guys over at E3Rehab have also recorded an interesting discussion with Dr. Jason Silvernail here. Lastly, you can find more information on sleep over at https://www.sleepfoundation.org/
References:
Assefa SZ, Diaz-Abad M, Wickwire EM, Scharf SM. The functions of sleep. AIMS Neuroscience. 2015 Aug 12;2(3):155-71.
National Institue of Neurological Disorders and Stroke. Brain Basics: Understanding sleep. 2019. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep
Schmidt MH. The energy allocation function of sleep: a unifying theory of sleep, torpor, and continuous wakefulness. Neuroscience & Biobehavioral Reviews. 2014 Nov 1;47:122-53.
Weitzman ED, NogeireO C, Perlow M, Fukushima D, Sassin J, McGregor P, Gallagher TF, Hellman L. Effects of a prolonged 3-hour sleep-wake cycle on sleep stages, plasma cortisol, growth hormone and body temperature in man. The Journal of Clinical Endocrinology & Metabolism. 1974 Jun 1;38(6):1018-30.
Spiegel K, Tasali E, Penev P, Cauter EV. Brief communication: sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Annals of internal medicine. 2004 Dec 7;141(11):846-50.
Walker MP, Brakefield T, Morgan A, Hobson JA, Stickgold R. Practice with sleep makes perfect: sleep-dependent motor skill learning. Neuron. 2002 Jul 3;35(1):205-11.
Nishida M, Walker MP. Daytime naps, motor memory consolidation and regionally specific sleep spindles. PloS one. 2007 Apr 4;2(4):e341.
Banks S, Dinges DF. Behavioral and physiological consequences of sleep restriction. Journal of clinical sleep medicine. 2007 Aug 15;3(5):519-28.
Goldstein AN, Walker MP. The role of sleep in emotional brain function. Annual review of clinical psychology. 2014 Mar 28;10:679-708.
Xie L, Kang H, Xu Q, Chen MJ, Liao Y, Thiyagarajan M, O’Donnell J, Christensen DJ, Nicholson C, Iliff JJ, Takano T. Sleep drives metabolite clearance from the adult brain. science. 2013 Oct 18;342(6156):373-7.
Altman NG, Izci-Balserak B, Schopfer E, Jackson N, Rattanaumpawan P, Gehrman PR, Patel NP, Grandner MA. Sleep duration versus sleep insufficiency as predictors of cardiometabolic health outcomes. Sleep medicine. 2012 Dec 1;13(10):1261-70.
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.
Brown FC, Buboltz Jr WC, Soper B. Relationship of sleep hygiene awareness, sleep hygiene practices, and sleep quality in university students. Behavioral medicine. 2002 Jan 1;28(1):33-8.
Chellappa SL, Steiner R, Oelhafen P, Lang D, Götz T, Krebs J, Cajochen C. Acute exposure to evening blue‐enriched light impacts on human sleep. Journal of sleep research. 2013 Oct;22(5):573-80.
Irish LA, Kline CE, Gunn HE, Buysse DJ, Hall MH. The role of sleep hygiene in promoting public health: A review of empirical evidence. Sleep medicine reviews. 2015 Aug 1;22:23-36.
Carskadon MA, Rechtschaffen A. Monitoring and staging human sleep. Principles and practice of sleep medicine. 2011;5:16-26.
Leger D, Richard JB, Collin O, Sauvet F, Faraut B. Napping and weekend catchup sleep do not fully compensate for high rates of sleep debt and short sleep at a population level (in a representative nationwide sample of 12,637 adults). Sleep Medicine. 2020 Jun 6.
Rupp TL, Wesensten NJ, Bliese PD, Balkin TJ. Banking sleep: realization of benefits during subsequent sleep restriction and recovery. Sleep. 2009 Mar 1;32(3):311-21.