Why Is Sleep So Important?
Christina Apthorp | 27 March 2017

Sleep deprivation is widely accepted to have adverse outcomes on people’s general functionality in the short term[1]. 20% of the British adult population have reported problems affecting their sleep[2]. Many researchers have tried to find quantitative evidence that there is a link between short sleep (<5hrs) duration and disease. However scientists still aren’t exactly sure why we sleep[10]. Sleep leaves humans in their most vulnerable state, so why did we evolve to spend a third of our lives under threat?

 

 

Studies have produced a potential link between sleep deprivation and the UK’s biggest killer: Cardiovascular Disease (CVD)³. CVD is defined as myocardial infarction, angina or stroke. Data from the 2005 National Health Interview Survey carried out in the USA was analysed. This person-to-person questionnaire gathered information from over 31,000 adults⁷. What they found was that sleep duration shorter than 5 hours was positively linked with all types of CVD. The same results have been found in other countries⁸. The authors suggest that this correlation is due to the disturbance of the metabolic and endocrine function. A causation that the increased sympathetic function leads to hypertension resulting in atherosclerosis which is known to directly cause CVD⁹. This same study also showed subjects who suffered from severe insomnia (complaints for > 1yr) and short sleep have a large and significantly increased risk of hypertension. As well there is the General Health Questionnaire section of the Whitehall II study ¹³ showing a longitudinal study which started in 1985 and followed the health of 10,308 men and women in the UK¹⁴. This paper identifies that there is a causal link between short sleep and disrupted sleep i.e. those who suffer from short sleep also suffer from sleep disruption. This shows adverse long term effects, which may be suggest failure of the body to repair and regenerate tissue that is causing the increased risk in CHD (something that is strongly linked to sleep disruption) and not just the short duration¹⁵.

 

 

 

In another paper the authors explore the possibility that it is the disturbance in immunity that sleep deprivation causes that leads to increased cardiac risk¹⁷. 19 young and healthy men participated in a week of physical screening that simulated a busy working week (4 nights of 4 hours sleep and 2 recovery nights of 8 hours). The physical screening comprised of polysomnography and extensive blood tests; in particular it was the proinflammatory cytokines that they were interested in. After the 5 days of sleep restriction an increase of some of these was observed. An additional observation this paper makes is that blood pressure was elevated after the five days of short sleep[10]. So whilst it is fair to say that sleep deprivation is almost certainly a factor in the prevalence of CVD, no mechanism has been determined[12].

 

 

Sleep also helps your brain cognitive function[20] . A theory by Reimund states that the function of sleep is the removal of excess cerebral free radicals (species with an unpaired electron) accumulated during wakefulness[24]. Increase in these radicals is linked to metabolic rate. These are removed in sleep by increasing efficiency of antioxidant mechanisms. This theory explains the correlated between smaller mammals and higher sleep amounts, as they have high metabolic rates. During sleep new pathways are formed to help retain and store information. When a body is lacking in sleep, it enters a state of stress, here body functions are on high alert. This increases blood pressure and causes the production of stress hormones (adrenaline), which in turn make it harder for us to fall asleep. During sleep, memory consolidation occurs whilst the body is resting, our brain is busy processing our day, and making connections between events, feelings, experiences and memories[18]. Sleeping time is the most important time for our brain to shape memories and make the connections, which can make it easier for us to retrieve those memories in the future[21]. Finally biochemical substance serotonin, a neurotransmitter that affects our mood, is produced in sleep. High serotonin levels create the feeling of happiness, and low serotonin levels can make us vulnerable to depression and other disorders[20]. Sleep deficiency can be linked to mental disorders such as depression, suicide, anger and impulsive behaviour. Making sure we are getting enough sleep, between 7 and 9 hours every night, will help us regulate serotonin levels, thus feeling happier and more productive[22].

 

 

Short sleep can lengthen the time taken to finish tasks, affecting reaction speed and the nervous system22, and contributes to more mistakes being made. Getting enough sleep at the right time of day helps your body’s performance function well throughout the day. People who are sleep deficient are less productive at work and school20. Studies show that even after a loss of just 1–2 hours per night over a period of time the brain’s ability to function suffers as if you haven't slept at all for a day or two. Shortness of sleep may also lead to microsleep - brief moments of sleep that occur when you're normally awake which you may not always be aware of23. Microsleep can affect how you function. An example of this is a tired driver who feels capable of driving. However studies show that sleep deficiency may harm your driving ability more than being a drunk driver. Estimations state that driver sleepiness is a factor of around 100,000 car accidents each year, resulting in about 1,500 deaths. As a result, sleep deficiency is not only harmful on a personal level, but it also can cause large-scale damage22.

 

 

In conclusion sleep is so Important: having effects on your physical well being -increasing risks of disease such as CVD; causing change in brain functions and mental health; as well as effecting your performance and safety. So, even cutting back on a few hours of sleep can’t be afforded, taking a toll on your mood, energy, and ability to handle stress.

 

Sleep Is So Important.

 

Bibliography

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2. Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep.

3. NHS Choices. Coronary heart disease 2012

4. WHO. 10 facts on obesity: WHO; 2013.

5. Knutson KL. Sleep duration and cardiometabolic risk: a review of the epidemiologic evidence. Best Practice & Research Clinical Endocrinology & Metabolism.

6. Sabanayagam C, Shankar A. Sleep duration and cardiovascular disease: results from the National Health Interview Survey. Sleep.

7. About the National Health Interview Survey: Centers for Disease Control and Provention

8. Shankar A, Koh WP, Yuan JM, Lee HP, Yu MC. Sleep duration and coronary heart disease mortality among Chinese adults in Singapore: a population-based cohort study. American Journal of Epidemiology.

9. NHS Choices. Atherosclerosis: NHS Choices; 2012

10. Copinschi G. Metabolic and endocrine effects of sleep deprivation. Essential Psychopharmacology.

11. Miller M. Biomarkers of cardiovascular risk in sleep-deprived people. Journal of Human Hypertension.

12. Vgontzas AN, Liao D, Bixler EO, Chrousos GP, Vela-Bueno A. Insomnia with objective short sleep duration is associated with a high risk for hypertension. Sleep.

13. Chandola T, Ferrie JE, Perski A, Akbaraly T, Marmot MG. The effect of short sleep duration on coronary heart disease risk is greatest among those with sleep disturbance: a prospective study from the Whitehall II cohort. Sleep.

14. HEALTH URDOEAP. Whitehall II (also known as the Stress & Health Study): UCL RESEARCH DEPARTMENT OF EPIDEMIOLOGY AND PUBLIC HEALTH;

15. Akerstedt T, Nilsson PM. Sleep as restitution: an introduction. Journal of Internal Medicine.

16. Institute for Work & Health. What researchers mean by...cross-sectional vs. longitudinal studies: Institute for Work & Health; 2009

17. van Leeuwen WM, Lehto M, Karisola P, Lindholm H, Luukkonen R, Sallinen M, et al. Sleep restriction increases the risk of developing cardiovascular diseases by augmenting proinflammatory

18. Vishnu A, Shankar A, Kalidindi S. Examination of the association between insufficient sleep and cardiovascular disease and diabetes by race/ethnicity. International Journal of Endocrinology.

19. Centers for Disease Control and Prevention. Behavioral Risk Factor Surveillance System: Centers for Disease Control and Prevention; 2013

20. NHS: Explore Sleep Deprivation and Deficiency

21. Coco Mat. Sleep on nature. Why is sleep so important

22. How stuff works: why is sleep that important. Charles W. Bryant

23. Helpguide: how much sleep do we need. Melinda Smith, M.A., Lawrence Robinson, and Robert Segal, M.A.

24. Reimund, E. The free radical flux theory of sleep.

James Routledge 2016