Sleep, a passive state of rest, is something all humans do, and it holds profound importance in our lives. It seems to help us relax and rejuvenate, but it also plays a critical role in our general well-being and health. The significance of sleep extends far beyond mere rest, impacting cognitive function, emotional stability, immune system and even physical health.

Sleep’s Role in Health

Figure 1: The five stages make one sleep cycle, which usually repeats every 90 to 110 minutes. Stage 1 marks the transition from wakefulness to sleep lasting around 10 minutes. Stage 2 is non-REM light sleep where the transition into deep sleep will begin, consisting of roughly 20 minutes. Formerly known as Stage 3 and 4, Stage 3 is the final stage of non-REM sleep, the deepest period of sleep that lasts around 20-40 minutes. Stage 5 refers to REM sleep, normally occurring 90 minutes after sleep onset, characterised by rapid eye movements, an almost complete paralysis of the body and a tendency to dream. Figure from Ruhl, 2023.

 

  1. Memory and Cognitive Function

Over the past decade, an important link between sleep and cognitive processing has been established. Sleep plays an important role in the consolidation of different types of memory and contributes to insightful, inferential thinking (Deak and Stickgold, 2010). Various attention, memory and neuropsychological test experiments have demonstrated that patients who are acutely sleep-deprived show deficits in verbal fluency, creative thinking and nonverbal planning amongst other issues that arose (Harrison and Horne, 1998). Sleep also has a role in memory consolidation and protection of said memories from inference (Fowler et al., 1973). It is understood that during the deeper cycles of sleep, stages 3 and 4 in Figure 1, that the brain processes and consolidates information from the day enhancing memory formation and retention. This is also why it is not surprising that sleep has been suggested to have a bidirectional effect on neurodegenerative diseases like Alzheimer’s disease (AD) where memory plays a key role (Ju et al., 2014) and has been suggested that sleep quality measurements can be an innovative method to screen for AD (Lucey et al., 2019).

  1. Immune system

Sleep is important for the body to build defences and recover from illnesses. This is why when people are sick, they tend to stay in bed and sleep a lot, this enables quicker healing and restoration of health. The biology is that during sleep, cytokines are released, these are immune system proteins that are important for immunity signaling and regulation. Some of these cytokines promote sleep, and other cytokines are crucial to counteract infection or inflammation. Sleep deprivation could decrease the production of these protective cytokines (Besedovsky et al., 2019). Therefore, sleep exerts immune-supportive functions and impairments of the immune-inflammatory system are a plausible mechanism mediating the negative health effects of sleep deprivation, and in particular, its role in the risk and outcomes of chronic diseases such as infections, cardiovascular, metabolic and autoimmune diseases, neurodegenerative diseases, and cancer (Garbarino et al., 2021).

  1. Physical recovery

Sleeping and physical resting is important after physical exercise. During deep sleep, the body releases growth hormones which allow for tissue repair and muscle growth. This reinforces the importance of rest days during the fitness journey. In addition, better sleep may reduce the risk of both injury and illness in athletes, not only optimising health but also potentially enhancing performance through increased participation in training (Watson, 2017). Furthermore, sleep allows the energy stores to be replenished which will support physical stamina and performance during waking hours.

  1. Brain waste clearance

During sleep, particularly in the deeper stages, such as non-REM sleep, the brain’s glymphatic system becomes significantly active (Xie et al., 2013). The glymphatic system refers to the perivascular metabolic clearance network in the brain that removes toxins and metabolic byproducts. This system works akin to the lymphatic system in the body, clearing away metabolic waste and toxins accumulated during waking hours. Through a complex process, cerebrospinal fluid washes through the brain, flushing out byproducts and waste from the brain. A decreased function in brain waste clearance function has been reported in AD and Parkinson’s disease (PD). An example of waste removal can be amyloid beta, a hallmark of AD. After a night of sleep deprivation, positron emission tomography has shown increased amyloid beta burden in brain regions implicated in AD pathology (Shokri-Kojori et al., 2018).

 

Sleep Disorders

Sleep apnea is a disorder characterised by interrupted breathing during sleep. It occurs several times during the night, leading to disrupted sleep patterns and reduced oxygen flow to the body and brain. There are several symptoms, which include loud snoring and excessive daytime sleepiness. It is also a risk factor for cardiovascular diseases, as it may lead to high blood pressure, heart problems and an increased risk of stroke (Baillieul et al., 2022). Treatment for sleep apnea varies depending on the type and severity of the condition. Lifestyle changes such as weight loss, positional therapy, avoiding alcohol and sedatives before bedtime, and using oral appliances or Continuous Positive Airway Pressure (CPAP) machines to keep the airway open are commonly recommended.

Insomnia is one of the most prevalent health concerns in the population and clinical practice. This disorder occurs when the individual has persistent difficulty falling asleep or staying asleep and is accompanied by symptoms of irritability or fatigue during wakefulness. It can be a presenting symptom for several common sleep disorders and it can be a risk factor for impaired function and development of other medical and mental disorders like depression (Taylor et al., 2003). Cognitive behavioural therapy for insomnia is the preferred treatment approach because of its efficacy, safety, and durability of benefit, but pharmaceutical treatments are widely used for insomnia symptoms.

Narcolepsy is the most common neurological cause of chronic sleepiness. It is a neurological disorder characterised by disturbances in the sleep-wake cycle, leading to excessive daytime sleepiness and disrupted nighttime sleep. Individuals with narcolepsy often experience sudden, uncontrollable episodes of falling asleep during the day, regardless of the circumstances or activity they are engaged in. These episodes, called “sleep attacks,” can occur multiple times a day and may last from a few seconds to several minutes. Beyond daytime sleepiness, narcolepsy can manifest with other symptoms such as cataplexy, where strong emotions trigger sudden muscle weakness or paralysis, vivid hallucinations upon falling asleep or waking up, and disrupted nighttime sleep with frequent awakenings. Narcolepsy can significantly impact daily functioning, affecting work, social interactions, and overall quality of life. Management of narcolepsy typically involves medications to regulate sleep-wake cycles, lifestyle adjustments, scheduled naps, and behavioural strategies to improve sleep quality and manage symptoms. However, recent research suggests narcolepsy is an autoimmune disorder that may be caused by a T cell-mediated attack on the orexin neurons, this understanding can improve therapeutic approaches (Mahoney et al., 2019).

Rapid eye movement (REM) sleep behaviour disorder (RBD) is a parasomnia characterised by dream-enactment behaviours that emerge during a loss of REM sleep atonia (Howell & Schenck, 2023). Atonia refers to skeletal muscle paralysis, a protective measure for when people dream. RBD dream enactment ranges in severity from benign hand gestures to violent thrashing, punching, and kicking. RBD is a risk factor for alpha-synuclein neurodegeneration which includes PD, multiple system atrophy and dementia with Lewy bodies (Lin and Chen, 2018). In fact, RBD confirmed by video polysomnography is among the strongest early predictors of PD (Postuma and Berg, 2016). Relating to other sleep disorders, it may also be a symptom of Narcolepsy, as around half of narcoleptics present symptoms of RBD (Schenck and Mahowald, 1992).

 

SleepTech Devices

There are many gadgets and apps that are designed to track, improve and promote healthy sleeping habits and also tackle various sleep disorders. A few examples are mentioned below.

Scientists at ETH Zurich are developing Somnomat Casa, which refers to a robotic bed that implements easy, back and forth gentle swaying motions that mimic parents rocking their babies. Another variation of it is targeted at people suffering from sleep apnea. The intelligent beds can detect apnea events, which is when airflow drops and breathing stops, using radar, sensor mattresses and microphones. The beds then elevate the sleeper’s torso or induce a sideward turn by inclining half of the bed.

The Oura Ring is a sleep device that it is worn like a ring on the finger, they can track heart rate, oxygen levels and physical movement. This data will allow the identification of sleep habit patterns and disturbances that can be tackled for improved sleep hygiene.

The Dreem headband monitors sleep by measuring brain activity, heart rate and movement with the precision of a sleep lab, but in the comfort of your own home and without all the cables and machines. They can play sounds that allow better-quality sleep and gentle waking. They can identify sleep patterns and even any underlying sleep disorders. Dreem also has an app that will then deliver personalised sleep restructuring exercises and tips, developed by experts.

 

Conclusion

Sleep guards the gates to our vitality and well-being, often undermined in the current society as productivity is often glorified at the expense of our essential need for rest. Sleep’s role varies from the orchestration of memory consolidation, and cognitive function to immune resilience and physical restoration. More emphasis should also be placed on various sleep disorders, as not only debilitating on their own, they seem to be biomarkers for other neurodegenerative diseases and neuropsychiatric disorders. One of the advances in therapeutics is the emergence of SleepTech, which offers hope in the battle against sleep problems, offering personalized solutions and insights into better sleep. Insights into the snooze science hopefully highlighted the importance of sleep habits and hygiene, not merely a luxury but an imperative foundation for our health and well-being.

 

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