Sleep! We can’t live without it
How much do you know about the impact of missing sleep? Surely missing a few hours’ sleep here and there won’t cause that much damage. After all, human beings are hugely successful adaptors – we’re at the top of the evolutionary tree – we’ll adjust to a little sleep loss, we just need to train ourselves to get used to it, right?
Neuroscientist and sleep expert, Matt Walker, would disagree with the notion that we’ll get used to it. Indeed, he summed up the impact of sleep loss very succinctly when he observed
“the shorter your sleep, the shorter your life.”
Let’s take a moment to think about the part sleep plays in our lives.
We spend approximately one-third of our lives sleeping. Given our evolutionary path has brought us to a place where we dedicate so much time to sleep, it shouldn’t surprise us to learn sleep is an essential part of our existence. Similarly, it shouldn’t surprise us to learn that if we miss something that important, it will have an effect.
And it’s not just Walker who thinks sleep loss is bad for you. The World Health Organisation and virtually anyone else who works in the sleep research field recommends at least seven hours’, preferably eight hours sleep’ a night is a good baseline level.
Our Sleep Cycle
So, what is going on when we are asleep? Our sleep can be divided into two parts: Rapid Eye Movement (REM) and non-REM. Non-REM sleep can be further broken into 4 stages (creatively called Stages 1, 2, 3 and 4). Stages 1 and 2 (S1 and S2) comprise light sleep, which prepares us for Stages 3 and 4 (S3 and S4) by lowering our body temperature and slowing our heart rate and brainwave activity. S3 and S4 are stages of slow-wave deep sleep. This is when our body recovers from the day’s activity, our cardio-vascular system is refreshed and our memories from the day currently stored in our Short-term Memory banks get fixed into the neural architecture of our Long-term Memory (LTM).
Next, we move into REM sleep. This is when we principally have our most vivid dreams. Our brain activity starts to speed up and receive a form of mental recovery and emotional first aid. This is also when we get a creativity boost. REM helps us to integrate information and solve problems from the day, enabling us to wake up with answers to our problems now that we’ve been able to “sleep on it”. We then spend the remainder of the night oscillating back and forth in roughly 90-minute bursts of REM and non-REM sleep, each cycle with an increasingly larger proportion of REM.
Already, we can see that when you lose sleep, you reduce the amount of deep sleep and REM sleep. And in so doing, you reduce the opportunity for mental recovery, emotional first aid, information integration, and the creativity boost that could help solve the day’s problems.
The Impact of Sleep Deprivation
So, how else does sleep loss affect us?
- Cognitive functioning. We can see from the above outline of our sleep cycle that we need to sleep after learning so that we integrate learning and move it into our LTM. Research also shows we need to sleep prior to learning. Without enough sleep, there is a 40% deficit in our ability to move information into our LTM. The hippocampus plays an important role in turning short-term memories into long term memories, and in retrieving memories, declarative memories (those related to facts and events) and spatial relationships. For very sleep-deprived people the hippocampus fails to show any significant activity at all, meaning there are few STMs to even turn into long term memories. Interestingly, earlier this year Howard LeWine reported a study that observed worse performance on brain testing among those who slept five hours or less hours per night and those who slept nine hours or more, compared with those getting seven to eight hours of sleep a night.
- Complex Decision-making. Early sleep deprivation (SD) research examining its effect on decision-making tended to focus on simple tasks sensitive to SD mostly because of their dull monotony. In contrast, decisions made in more complex rule-based, convergent, and logical tasks are unaffected by short-term SD, seemingly because of heightened interest and compensatory effort. However, recent research has shown that despite this extra effort, SD still impairs decision-making requiring innovation, the revision of plans, competing distractions, dealing with the unexpected, and effective communication. Neuropsychological explanations of sleep function provide useful perspectives on these latter effects, especially for decision-makers who require these skills during emergency situations.
- Aging and Dementia. It’s no secret that, as we get older, our cognitive functioning declines. Recent research has also found that as we age our sleep quality deteriorates, especially deep sleep. More importantly, it was recently shown that these two things are not simply co-occurring. They are significantly interrelated and declines in our sleep quality contribute significantly to our cognitive decline and Alzheimer’s. While there’s little we can do about the decline in our brain’s structure as we age, we can do something about the quality of our sleep.
- Cardiovascular System. Every year, 1.6 billion people across 70 countries shift their time zone in a biannual process, we know as daylight saving time (DST). When we start DST, we lose one hours’ sleep, and the very next day we see a 24% increase in heart attacks. When DST finishes and we gain an hours’ sleep, there is a 21% reduction in heart attacks. Siestas have been also associated with a 37% reduction in coronary mortality, possibly because of reduced cardiovascular stress associated with daytime sleep. Whether the most important feature of this is the daytime nap itself, a supine posture, or the expectancy of a nap is unknown.
- Immune System. Natural Killer (NK) cells are part of your body’s immune defence. When we sleep less we have less NK cell activity. For example, a loss of four hours’ sleep in just one night results in a 70% drop in your NK cell activity – a significant change in your immune protection. Research indicates significant connections between reduced sleep and the risks of developing a number of cancers, including the bowel, prostate and breast cancer. In fact, the connection between sleep loss and cancer is so significant, the World Health Organization now classifies shift work as a probable carcinogen.
- DNA structure. A loss of sleep also erodes your DNA code. Simply limiting sleep to six hours a night for one week, had a dramatic effect on those individual’s gene activity profile relative to when they had a full eight hours of sleep. And there were two critical findings. The results showed that 711 genes were distorted in their activity, with about half of those genes increasing their activity, and the other half decreasing it. The concerning aspect of this finding was that the genes with reduced activity were associated with your immune system, meaning their reduced activity reduced your immune response. In contrast, those genes with increased activity were associated with the promotion of tumours, long-term chronic inflammation in the body, and stress, and as a consequence with increased cardiovascular disease.
Tips for Getting Better Sleep
Given how dramatic an impact sleep loss can have, what can you do to make sure you get enough good sleep?
- Don’t drink alcohol too close to sleep – alcohol might make you feel tired, but it inhibits REM sleep, increases restlessness and waking, and sometimes causes headaches and night sweats.
- Don’t drink Caffeine too close to sleep. Caffeine is a stimulant. While most know that an after-dinner coffee will disrupt your sleep, don't forget other less considered sources such as chocolate, cola, tea, and some medications (e.g., pain relievers, weight loss pills, diuretics, cold medicines).
- Don’t use sleeping tablets – most will inhibit sleep quality.
- Don’t take naps during the day – they reduce your need for night-time sleep.
- Don’t overeat, especially high-fat food within 60 to 90 minutes before sleep – as well as promoting weight-gain, too much high-fat food will activate digestion disrupting sleep cycles.
- Do ensure regularity – go to bed at the same time, wake up at the same time. This will anchor your sleep and improve the quantity and the quality of that sleep.
Do stay cool – both physically and psychologically:
- Physically, your body needs to drop its core temperature by one or two degrees Celsius to get to sleep and then to stay asleep – a room temperature of around 20 degrees Celsius should be optimal for most people.
- Psychologically, getting anxious about not sleeping activates your fight or flight response which does not help you sleep.
Do eat right, especially in the 60 to 90 minutes before you sleep:
- Dairy can help you sleep – it contains tryptophan, which promotes sleep. Good sources of dairy include milk, cheese, and eggs. Other sources are nuts, seeds, bananas and honey.
- Carbohydrates also help. Some good late-night snack options include cereal and milk, bread and cheese, or a honey sandwich.
- Keep snacks light – a little food in your stomach can help sleep, but too much will make you more restless as you digest what you’ve eaten.
So much of our daily lives, our health and wellness, and our longevity are impacted by sleep loss. In the words of Matt Walker
“there is simply no aspect of your wellness that can retreat at the sign of sleep deprivation and get away unscathed”.
- Walker, M. (2017). In You are probably not getting enough sleep, and it is killing you by H. Brueck, Business Insider Australia, Nov, 2017.
- Xu, W., Tan, C-C., Zou, J-J., Cao, . X-P., and Tan, L. (2019). Sleep problems and risk of all-cause cognitive decline or dementia: an updated systematic review and meta-analysis. Journal of Neurology, Neurosurgery and Psychiatry, 91(3). DOI: org/10.1136/jnnp-2019-321896
- LeWine, H., (2020). Too little sleep, and too much, affect memory. Harvard Health Blog, updated June 2020.
- Harrison, Y., and Horne, J.A. (2000). The Impact of Sleep Deprivation on Decision-Making: A Review. Journal of Applied Experimental Psychology, 6(3), 236-49. DOI: 10.1037//1076-898X.6.3.236.
- Spira, A.P., Chen-Edinboro, L.P., Wu, M.N., and Yaffe, K. (2014). Impact of Sleep on the Risk of Cognitive Decline and Dementia. Current Opinion in Psychiatry, 27(6), 478–483.
- Manfredini, R., et al. (2019). Daylight Saving Time and Acute Myocardial Infarction: A Meta-Analysis. Journal of Clinical Medicine, 8(3), 404. DOI: 10.3390/jcm8030404.
- Zaregarizi, M., Edwards, B., George, K., Harrison, Y., Jones, H., and Atkinson, G. (2007). Acute changes in cardiovascular function during the onset period of daytime sleep: comparison to lying awake and standing. Journal of Applied Physiology. DOI:10.1152/japplphysiol.00474.2007
- Irwin, M.R., Mascovich, A., Gillin, J.C., Willoughby, R., Pike, J., Smith, T.L. (1994). Partial sleep deprivation reduces natural killer cell activity in humans. Psychosomatic Medicine, 56(6):493-498.
- Imai K, Matsuyama S, Miyake S, Suga K, Nakachi K (2000). Natural cytotoxic activity of peripheral-blood lymphocytes and cancer incidence: an 11-year follow-up study of a general population. Lancet, 356(9244):1795-1799.
- Irwin MR, Wang M, Campomayor CO, Collado-Hidalgo A, Cole S (2006). Sleep deprivation and activation of morning levels of cellular and genomic markers of inflammation. Archives of Internal Medicine, 166(16):1756-1762.
- Cheung, V., Yuen, V.M. Wong, G.T.C., and Choi, S.W. (2019). The effect of sleep deprivation and disruption on DNA damage and health of doctors. Anaesthesia, 74, 434–440.
- Walker, M. (2019). In Sleep is your superpower. Found at www.ted.com/talks/mattwalkersleepisyour_superpower.