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What Is Sleep?

September 13th, 2023

Having trouble staying awake in meetings? 

Struggling to unwind and get to sleep?

Are you becoming forgetful and frustrated? 

Does this sound familiar? Well you are not alone! When living a demanding lifestyle requiring constant attention to detail, deadlines and consequences, it can be an overwhelming task to fit sufficient sleep into your schedule.

What Is Sleep?

Sleep is a complex physiological process characterised by eye closure, reduced body movement, responsiveness to external stimuli, altered body position and brain wave activity [1].  Sleep is thought to play an important role in several vital functions including amongst others cellular restoration, development, brain waste clearance, and modulation of immune responses [1].

Sleep is known to proceed through several stages: 3 stages of non-rapid eye movement or NREM which are associated with increasing depth of sleep and 1 stage of rapid eye movement or REM sleep. A person will typically cycle through these stages 4 to 5 times during a night’s sleep with each cycle lasting around 90 minutes [1]. These cycles are controlled by your internal biological clock also known as your circadian rhythms. 

The duration of sleep your body requires, often depends on your age [2]. On average adults need 7 to 9 hours of sleep per night while children may need considerably more sleep than adults as they are going through a second stage of development [2]. 

Why Is Sleep So Important?

If you are not getting enough sleep or are not sleeping well, this can have a significant impact on several vital functions. When you are asleep, your body can engage in the process of recovery.  This is supported by the many restorative processes including muscle repair, tissue growth, protein synthesis, and the release of the important hormones for growth occurs during the night.

In the young insufficient sleep can also have an impact on brain development as evidenced through structural changes and can contribute to mental health and behavioural issues. A recent study found that those children who had less than nine hours per night had less grey matter or smaller volume in areas of the brain responsible for attention, memory, and inhibition control, compared to those with healthy sleep habits [3]. 

The brain’s waste management system known as the glymphatic system is also only active during sleep [4]. This system aids in the removal of soluble proteins and metabolites from the central nervous system and supplies the brain with glucose, lipids, amino acids, growth factors, and neuromodulators [4]. Impaired glymphatic clearance has been linked to a range of neurodegenerative disorders including Alzheimer’s disease [4].

A lack of sleep is also known to affect the functioning of the immune system. A moderate amount of sleep loss can lead to a reduction in natural killer cell levels, which are known to display important anti-cancer activity [5]. Research has also shown that sleep deprivation can lead to the generation of higher levels of inflammatory cytokines which play a role in the development of cardiovascular and metabolic disorders [6]

Not getting enough sleep can also impact cognitive processes including the consolidation of memories. Memory consolidation is the process by which a temporary, labile memory is transformed into a more stable, long-lasting form. Memory consolation is thought to occur during both the NREM and the REM stages of the sleep cycle [7]. The presence of sleep disorders including obstructive sleep apnoea has been associated with cognitive decline and memory problems [8].

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Are You Displaying Any of These Signs?

To determine if we are getting enough sleep consider whether you are displaying any of the following signs:

  • Muscle aches

  • Yawning throughout the day

  • Feeling lethargic

  • Mood changes, including feeling stressed, anxious or paranoid

  • Struggling to get out of bed

  • Needing to sleep later at the weekends 

  • Having difficulty focusing or remembering

  • Falling asleep during the day while carrying out your normal daily activities


It is apparent that a lack of sleep can have a significant impact on your physical and mental functions. If you are displaying any of the symptoms listed above then it is likely that you are suffering from sleep deprivation and it is important that you take steps to ensure you are getting adequate sleep.

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[1] R. Zielinski M, T. McKenna J, W. McCarley R. Functions and Mechanisms of Sleep. AIMS Neurosci. 2016;3:67–104.

[2] National Health Service. Insomnia [Internet]. [cited 2023 Sep 2]. Available from:

[3] Yang FN, Xie W, Wang Z. Effects of sleep duration on neurocognitive development in early adolescents in the USA: a propensity score matched, longitudinal, observational study. Lancet Child Adolesc Health. 2022;6:705–712.

[4] Reddy OC, van der Werf YD. The Sleeping Brain: Harnessing the Power of the Glymphatic System through Lifestyle Choices. Brain Sci. 2020;10:868.

[5] Irwin M, Mascovich A, Gillin JC, et al. Partial sleep deprivation reduces natural killer cell activity in humans. Psychosom Med. 1994;56:493–498.

[6] Irwin MR. Sleep Deprivation and Activation of Morning Levels of Cellular and Genomic Markers of Inflammation. Arch Intern Med. 2006;166:1756.

[7] Rasch B, Born J. About sleep’s role in memory. Physiol Rev. 2013;93:681–766.

[8] Krysta K, Bratek A, Zawada K, et al. Cognitive deficits in adults with obstructive sleep apnea compared to children and adolescents. J Neural Transm. 2017;124:187–201.

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