Sleep is a wonderful aspect of life that can often be either an enigma or a non-priority to some people. It is a strange evolutionary trait which renders all organisms vulnerable to attack and predation due to the inducement of a state of perceived unconscious paralysis. This highlights how essential sleep must be for life as some form of it is performed by every organism on the planet (even bacteria have a primitive form of a sleep/wake cycle), even though it puts them at increased danger.
There are multiple interventions that can help support healthy sleep, this is very dependent on the individual as it is also affected by multiple factors. It is advisable to consult a health practitioner who can help to support healthy sleep, as it is not a one size fits all solution. Additionally, there will be a follow up blog for interventions to support healthy sleep very soon.
It has long been understood that sleep is fundamental for survival, however the reasons why were not, and even now the exact mechanisms of its full importance are still to be ascertained. This blog aims to highlight the importance of sleep as well as the consequences of poor sleep.
Stages of sleep
As we sleep, we transition through various phases from light non-REM (NREM) sleep to deeper NREM sleep or slow wave sleep, and into REM sleep. REM stands for Rapid Eye Movement, REM sleep is associated with the period of sleep when we dream, during this time we are effectively paralysed (as have lost all muscle tone) to prevent us from living or acting out our dreams. During NREM sleep no eye movement is detected, although the body muscles still have some tone. Deep NREM sleep is also known as slow wave sleep where our brain exhibits the lowest amount of brain wave activity and is considered to be restorative. It has often been wondered which is more important or essential, numerous studies have agreed that both play different roles but are essential for life.1
We sleep in 90-minute cycles of lighter NREM into deep NREM and then to REM sleep. However, this is not in perfect proportions, the early part of night has a higher proportion in NREM sleep and the latter half a higher proportion of REM. A balance of both is important for health, and particularly memory consolidation. This is a bit simplistic as many things are happening, but it seems NREM sleep is more involved in transference of short term to long term memory as well as weeding out unnecessary connections that have developed during the day. REM sleep is involved in fine tuning connections, supporting synaptic plasticity and accelerating complexity and connectivity. However, one cannot work effectively without the other.1
The discovery of fire was a remarkable breakthrough for Homo sapiens. Fires allowed them to be safe at night from predators and therefore they no longer had to sleep in trees. Previously the need to sleep off the ground in a tree would mean that a very limited amount of time could be spent in REM sleep as it was difficult to stay in a tree when muscles were fully relaxed. The ability to sleep on the ground allowed Homo sapiens to spend a much longer period of time in REM sleep. The opportunity to bathe the brain in REM sleep allowed for a higher amount of synaptic interconnectivity and support for neurodevelopment which increased our degree of sociocultural complexity and cognitive intelligence. This allowed for an enormous acceleration in social, cultural, and intellectual evolution, putting us on the path to modern humans and demonstrates the importance of REM sleep on cognitive development.1
It is therefore not surprising that our ratio of NREM and REM sleep alters throughout stages of our lives.
Prebirth– a foetus will spend up to 12 hours per day in REM sleep, as it is vital for promoting brain maturation acts as an electrical fertilizer developing neural pathways and encouraging synaptogenesis.
Infants – by the time a baby is 6 months old the is a 50:50 of NREM and REM sleep.
Children – A 5 year old will have a 70:30 ration of NREM:REM. This is showing that REM sleep in continuously decreasing throughout childhood.
Adolescence – by this time NREM sleep is dominant with and 80:20. NREM is vital for pruning connections and deep (NREM) sleep driving force of brain maturation this may be why rationality may be a problem in adolescents.
Adulthood – NREM decline begins to decline after adolescence with the ratio of REM sleep increasing again.
Elderly – sleep efficiency reduces with NREM taking the biggest hit, leaving REM sleep much more dominant.1,2
These alterations to the REM/NREM balance highlight that at different stages of life there is sometimes higher requirement for stimulating neurogenesis and synaptogenesis to support cognitive development and brain maturation, whereas at other stages the maintenance and weeding out of unwanted connections take a greater priority. However, as mentioned, as we age sleep efficiency decreases. It is likely that it is not that the elderly have a reduced requirement for sleep, particularly NREM sleep, but that sleep becomes less efficient and that NREM sleep is sacrificed. This reduction is sleep efficiency as we age is, at least in part, attributable to many health conditions that are associated with advancing age.1,2
Sleep and Alzheimer’s
It may seem quite obvious that sleep plays an essential role in protecting our cognitive health, however, how sleep protects our brains is not fully understood. Possible mechanisms underlying the reciprocal relationship between the sleep–wake cycle and AD pathology and behaviour include:
- Decreased neuronal activity during slow-wave sleep i.e. slow wave sleep gives neurons a “rest” allowing them to repair and recuperate
- Deficits in resting state functional connectivity, i.e. during rest new connections between neurons are formed
- Glial-mediated circadian clearance of soluble Aβ, i.e. amyloid-beta is cleared during sleep
- Clearance of toxic proteins from the interstitial space during sleep
- Reduction of pro-inflammatory cytokines (neuro-inflammation is a driver of dementia)
“Efficient and effective sleep is more than just a luxury; it is critical for the proper function of many organ systems, particularly the brain.” Musiek et al 2015
Although studies support the idea that sleep disturbances increase the risk of AD, there is also certainly evidence that amyloid deposition, damage to the sleep/wake regions of the brain as well as decreased cognitive and physical function associated with AD can also contribute to poor sleep. This creates a vicious cycle of poor sleep and further amyloid deposition, damage and reduced activity therefore exacerbating the problem. Although there is still some debate over this “chicken and egg” situation, when supporting patients with AD (or chronic sleep problems) it is a simpler intervention to improve sleep quality rather than to reduce Aβ, tau or brain injury. It is also important to be aware of the risk that chronic sleep deprivation can bring and therefore prioritise sleep support for individuals with sleep problems.3
Sleep and cancer
Poor sleep stimulates the sympathetic nervous system, provoking sustained inflammatory response. This sustained inflammation is a driver of cancer due to the initiation of angiogenesis, creating damage and mutations to DNA and helping to trigger metastasis. Therefore, poor sleep has an
impact on amplifying and spreading cancer progression. Additionally, sleep deprivation reduces M1 macrophages which possess anti-tumour properties and boosts M2 macrophages which have been shown to promote cancer growth. In vitro studies have shown that sleep deprived mice have a 200 percent increase in the speed and size of cancer growth.4-5
Sleep and cardiovascular disease
Sleep has a direct effect on our cardiovascular system and is insufficient sleep persists then it can have a significant impact and be a driving force of cardiovascular disease. This phenomenon occurs due to multiple reasons but not least due to over activation of the sympathetic nervous system. Poor sleep impacts the cardiovascular system by:
- Accelerating heart rate
- Increasing blood pressure
- Eroding blood vessel endothelium
- Sleeping only 5-6 hours per night means you are 200-300% more likely to suffer calcification of coronary arteries.
- People over the age of 45 who sleep 6 hours or less are at a 200% increased risk of heart attack.
Twice every year the biggest sleep study in the world is carried out 1.5 billion people worldwide are forced to lose or gain one hour sleep, during daylight savings when one hour is lost there is a spike in heart attacks the following day, when the hour is regained, 6 months later, the heart attack rates plummet the day after. Incidentally, similar relationships are seen with traffic accidents.
It should also be noted that poor sleep can be a trigger of obesity which has association with multiple health conditions, including cardiovascular disease. Again, this process is multi-factorial but even one night of poor sleep increases out hunger hormone ghrelin and reduces out satiety hormone leptin, thereby encouraging an increase in food intake and preventing normal balance of energy intake and expenditure, which has implications to weight management.6
Sleep and immune health
Sleep loss alters immune function and immune challenges alter sleep. Thus, chronic sleep loss results in pathologies that are associated with increases in inflammatory mediators, and inflammatory mediators that are released during immune responses to infection alter CNS processes and behaviour. Recent studies have also shown that short periods of sleep loss at the time of vaccination reduce the vaccine’s effectiveness.
It can be seen that sleep plays a major influence on health, and this list is not exhaustive, it has an impact of very organ system within the body. Therefore, prioritising sleep throughout life is important for maintaining wellness, throughout life but particularly into old age.7-9
For further information about how to support sleep health in yourself and your clients, see our webinar event for health practitioners, The Power of Sleep.
Lifestyle techniques to support sleep
- Try relaxation promoting activities such as yoga, yoga nidra, meditation, mindfulness, breathing and massage
- Take a warm/hot Epsom salt (a handful) bath before bed to aid sleep and relaxation. Hot baths bring blood vessels to the surface allowing your core body temperature to cool which helps the body prepare for sleep as body temperature begins to drop during night
- Ensure daytime full light exposure as well as activity, take a run or walk during daylight hours to top up on serotonin and vitamin D. Ensure you don’t exercise too late in the evening as can delay sleep onset
- Keep noises down (earplugs might help)
- Keep the room cool. Most people sleep best at around 18oC with adequate ventilation
- Make sure the bed is comfortable. Waking often with a sore back or neck suggests the mattress or pillow may need changing
- Create an aesthetic environment that encourages sleep – use serene and restful colours and eliminate clutter and distraction
- Avoid work or watching television in bed
- Consider using a relaxation, meditation or guided imagery app, any of these may help with getting to sleep and will certainly help with relaxation
- Cut down on caffeine. Ideally no caffeine after midday – some people take 12 hours to metabolise caffeine. Make sure this includes any medication that contains caffeine e.g. headache tablets (if prescription medication contains caffeine, discuss with the G.P. before stopping any medication)
- Sleep is essential to life and issues can contribute to multi chronic conditions. Therefore, supporting sleep health clinically should be a priority when considering wellness
- We sleep in 90-minute cycles of lighter NREM (non-Rapid Eye Movement) into deep NREM and then to REM (Rapid Eye movement) sleep (where we dream). In simple terms REM sleep supports synaptogenesis and neurogenesis therefore support rich cognitive development. NREM sleep is involved in weeding out unwanted connections and it particularly restorative. Sleep is essential for memory as this is where consolidation of the day’s memories occur and the transference from short term to long term memory storage
- The proportion of NREM to REM sleep changes throughout different stages of life. In the elderly sleep efficiency is reduced at the expense of NREM sleep in particular. This loss of sleep is correlated with and increased prevalence of chronic disease
- Poor sleep increases the risk of Alzheimer’s Disease, cancer, cardiovascular disease obesity and poor immunity
- Recent studies have also shown that short periods of sleep loss at the time of vaccination reduce the vaccine’s effectiveness
If you have questions regarding the topics that have been raised, or any other health matters, please do contact me (Helen) by phone or email at any time.
Amanda Williams and the Cytoplan Editorial Team
- Matthew Walker, (2017) Why we sleep. Penguin Books.
- Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten HR, Altevogt BM, editors. Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem. Washington (DC): National Academies Press (US); 2006. 2, Sleep Physiology. Available from: https://www.ncbi.nlm.nih.gov/books/NBK19956/
- Musiek, E., Xiong, D. & Holtzman, D. Sleep, circadian rhythms, and the pathogenesis of Alzheimer Disease. Exp Mol Med 47, e148 (2015). https://doi.org/10.1038/emm.2014.121
- Hakim F, Wang Y, Zhang SX, Zheng J, Yolcu ES, Carreras A, Khalyfa A, Shirwan H, Almendros I, Gozal D. Fragmented sleep accelerates tumor growth and progression through recruitment of tumor-associated macrophages and TLR4 signaling. Cancer Res. 2014 Mar 1;74(5):1329-37. doi: 10.1158/0008-5472.CAN-13-3014. Epub 2014 Jan 21. PMID: 24448240; PMCID: PMC4247537.
- Almendros I, Wang Y, Becker L, Lennon FE, Zheng J, Coats BR, Schoenfelt KS, Carreras A, Hakim F, Zhang SX, Farré R, Gozal D. Intermittent hypoxia-induced changes in tumor-associated macrophages and tumor malignancy in a mouse model of sleep apnea. Am J Respir Crit Care Med. 2014 Mar 1;189(5):593-601. doi: 10.1164/rccm.201310-1830OC. PMID: 24471484; PMCID: PMC3977714.
- Grandner MA, Alfonso-Miller P, Fernandez-Mendoza J, Shetty S, Shenoy S, Combs D. Sleep: important considerations for the prevention of cardiovascular disease. Curr Opin Cardiol. 2016;31(5):551-565. doi:10.1097/HCO.0000000000000324
- Imeri L, Opp MR. How (and why) the immune system makes us sleep. Nat Rev Neurosci. 2009;10(3):199-210. doi:10.1038/nrn2576
- Besedovsky L, Lange T, Born J. Sleep and immune function. Pflugers Arch. 2012;463(1):121-137. doi:10.1007/s00424-011-1044-0
- Zimmermann P, Curtis N. Factors That Influence the Immune Response to Vaccination. Clin Microbiol Rev. 2019 Mar 13;32(2):e00084-18. doi: 10.1128/CMR.00084-18. PMID: 30867162; PMCID: PMC6431125.