This article is the first in a three part series which will look into the importance of sleep on academic performance and health. This first article will delve into the science of sleep to understand its importance and purpose.
The earliest available documented theory of sleep is from around 450 BC by a Greek physician and philosopher named Alcmaeon of Croton who proposed that sleep was the result of blood withdrawing from the surface of the body to larger vessels 1. Since then science has proven that sleep is a more complex process than previously thought, and is not just a period in which the body relaxes and the mind dreams. We have yet to fully unravel the mysteries of sleep, but for now research has revealed that sleep is necessary for survival, daily functioning, health and wellbeing. An average person spends about one third of their lives sleeping. The duration of sleep varies between people depending on their age and their individual circumstances (e.g. students sleep less during exams). There is no hard and fast rule on how much sleep a person should have at night, but only recommended time ranges which vary between age groups. The National Sleep Foundation of USA had conducted a study to determine sleep duration recommendations for healthy individuals 2, and their recommended sleep times chart can be viewed via the following link: http://goo.gl/SXOnnx.
What is the role of sleep?
From experience it is known that if one stays awake all night how difficult it is to function the next day; there is a terrible feeling, drowsiness, irritability, tiredness, thinking and concentrating become difficult tasks which in turn affect rational judgment. Prof. William Dement known as the father of sleep medicine started the world’s first sleep laboratory, at Stanford University in 1970. After 50 years of pioneering sleep research he says “As far as I know, the only reason we need to sleep is because we get sleepy.” Although the physiological mechanisms of sleep are being discovered the exact role which it plays is still an enigma.
What makes us sleepy?
The alteration between being awake and sleep is mediated by complex neurobiological processes 3. Researchers have come up with a two process model which switch us on and off; the circadian biological clock and a ‘sleep / wake’ restorative process 4.
Our body’s circadian biological clock (situated in the brain) controls the circadian rhythms which are physical, mental and behavioural changes that follow a 24 hour cycle thereby regulating the periods of sleepiness and wakefulness each day. Melatonin which is a hormone regulated by the circadian clock is produced in the brain after sunset. Throughout the night the concentration of Melatonin in our system rises sharply making us feel sleepy, and in the morning this process becomes completely reversed.
The sleep / wake restorative process is a load on the body a ‘need to sleep’. When awake substances naturally produced by the body build-up in the brain; the best known such sleep regulating substance for now is Adenosine 5. The longer we stay awake the more these substances accumulate and the stronger the desire and pressure for sleep becomes. The longer healthy sleep an individual gets the more these substance concentrations reduce resulting in a greater likelihood of awakening refreshed.
These two vital systems work together to make sure the body receives enough sleep so that we achieve peak performance in life and work each day. However even with the existence of such systems which regulate our sleep and wakefulness fairly precisely, we are still able to temporarily ignore them voluntarily to pursue other activities such as studying throughout the night for exams or working night shifts, however this is not without consequence and will be discussed in detail in the second and third parts of this article.
Stages of sleep
There are two different alternating stages beginning with Non-Rapid Eye Movement (NREM) sleep and progressing to Rapid Eye Movement (REM) sleep. NREM sleep is divided into four separate stages: stage one is a transition from wakefulness in to sleep, and stage two is light sleep. In stages three and four the sleep gradually transitions from moderate to deep sleep. During these last two stages of deep sleep the body restores and repairs itself, and performs many other activities. The REM stage is characterised by rapid movements of the eye balls beneath the closed eyelids. During REM sleep the brain and body is supplied with energy and dreams occur. Dreams in REM sleep are very vivid therefore the skeletal muscles become paralysed during this stage as a protective measure to prevent us from physically acting out our dreams. Dreaming still remains a mystery which baffles both philosophers and scientists to this day.
During the course of the night the stages of sleep do not follow each cycle in sequence, and an example of a typical eight hour night’s sleep can be seen in Figure 1. Humans spend the majority of the night in NREM sleep and only about 25% in REM sleep. Therefore the recommended periods of sleep are required so that we go through all the different stages each night to allow our bodies to heal and restore itself and stay healthy.
Figure 1. Stages of sleep during a typical night’s sleep in healthy individual.
Quantity versus quality of sleep
What is interesting is that the quality of sleep is just as important as the quantity (duration) of sleep. In 2008 a group of researchers decided to define sleep quality 6. It was concluded that a definition of sleep quality should include tiredness on waking and throughout the day, feeling rested and restored on waking, and the number of awakenings in the night. Awakenings at night result in poor sleep quality, and disruptions can be caused by street noises, a crying baby, etc. Repeated interruptions to the sleep cycles can deprive an individual of deep sleep thus resulting in feeling tired in the morning.
Sleep Disorders
These refer to disorders which interfere with normal healthy sleeping patterns required for functioning normally during the day time. Sleep disorders can lead to mental or physical health problems. The International Classification of Sleep Disorders 7 which is a manual for clinicians and researchers provides an extensive list of sleep disorders. The following is a list of the most common sleep disorders.
Insomnia refers to a difficulty in falling asleep or staying asleep. There are various different causes such stress, anxiety, depression, a change in environment, certain medications, stimulants (coffee, energy drinks), and medical conditions (e.g. pain from arthritis) are examples.
Sleep apnoea is a serious sleeping disorder characterised by recurrent episodes of abnormal pauses in breathing during sleep. Obstructive sleep apnoea is the commonest form which occurs when the when throat muscles relax and blocks the flow of air to the lungs. High blood pressure, heart disease are serious complications of this disorder.
Restless legs syndrome sufferers have an irresistible urge to move the legs when lying down, often accompanied by uncomfortable or painful symptoms which are temporarily relieved when moving the legs, which in turn makes it difficult to get proper night’s sleep. The exact cause is yet unknown, but does have a genetic component involved as it has a tendency to run in families, and sometimes occurs during pregnancy but disappears after delivery of the child.
Narcolepsy sufferers have uncontrollable and excessive daytime drowsiness and sleep attacks at inappropriate times, such as at work. Complications include physical harm (e.g. falling asleep while driving), and poor performance in school or at work. There is no cure for narcolepsy it can only be controlled with medication and lifestyle modifications.
Behaviourally- Induced Insufficient Sleep Syndrome is a long term voluntary restriction of sleep resulting in daytime sleepiness and fatigue. As the name suggests it is caused by an individual’s behaviour; restricting sleep to pursue other activities such as work, watching television, and browsing the internet are a few examples. Consequences of insufficient sleep syndrome have been linked to an increased risk of automobile accidents, poor academic and job performance to name a few.
Sleep hygiene
Sleep hygiene refers to habits and rituals which will help to get quality and quantity of sleep you need to feel refreshed in the morning and have full daytime alertness.
- Maintain a consistent routine: go to bed at the same and get up from bed at the same time daily.
- Avoid stimulants such as coffee, cigarettes, and alcohol too close to bedtime.
- Regular exercise promotes sleep, preferably done during the mornings or afternoons.
- Adequate exposure to natural light helps to maintain healthy sleep-wake cycles.
- Avoid eating large meals before bedtime.
- Avoid nightlights if possible and keep the bedroom dark to facilitate sleep so that Melatonin production increases.
- Do not read or watch television in bed when its bedtime.
- Do not start checking email, browsing the internet or chat on your mobile device when you get into bed.
- A comfortable pillow and mattress will help you fall asleep faster.
- Avoid long daytime naps as it can affect the length and quality of night-time sleep
References
- Codellas, P. S. Alcmaeon of Croton: His Life, Work, and Fragments. Proc. R. Soc. Med. 25, 1041–6 (1932).
- Hirshkowitz, M. et al. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Heal. 1, 40–43 (2015).
- Saper, C. B., Chou, T. C. & Scammell, T. E. The sleep switch: Hypothalamic control of sleep and wakefulness. Trends Neurosci. 24, 726–731 (2001).
- Borbély, A. A. A two process model of sleep regulation.
- Huang, Z.-L., Urade, Y. & Hayaishi, O. The Role of Adenosine in the Regulation of Sleep. Curr. Top. Med. Chem. 11, 1047–1057 (2011).
- Harvey, A. G., Stinson, K., Whitaker, K. L., Moskovitz, D. & Virk, H. The subjective meaning of sleep quality: a comparison of individuals with and without insomnia. Sleep 31, 383–93 (2008).
- Thorpy, M. J. Classification of sleep disorders. Neurotherapeutics 9, 687–701 (2012).
Dr Kaushalya Jayaweera