What is sleep?

Sleep is the regular period in every 24 hours when we are unconscious and unaware of our surroundings(Ref. 1). In humans, sleep is usually one consolidated period occurring at night. Sleep provides important rest and restoration for the mind and the body; however the brain is very active during certain periods of sleep.

WHY DOES THE BODY NEED SLEEP?
Sleep is vital for survival and has important functions for systems in the body, including the endocrine, immune, cardiovascular, metabolic and nervous systems. Studies suggest that sleep performs a crucial role in bodily restoration, energy conservation and memory function. Some examples of how sleep deprivation can impact on daily functioning and health are:

• Mental health: Sleep is thought to have an important impact on intellectual performance, with many studies suggesting a 15% improvement in memory and mental agility after a good night’s sleep(Ref. 2).
• Obesity: A growing body of research suggests a link between sleep deprivation and obesity. One study found that sleep deprived individuals had 15% more of the hormone ghrelin, an appetite stimulating hormone, and 15% less of leptin, an appetite suppressor(Ref. 3).
• Endocrine systems: A lack of sleep may lead to decreased glucose tolerance, a possible precursor of type 2 diabetes(Ref. 4). Many hormones are secreted during sleep, including human growth hormone, cortisol and sex hormones such as luteinising hormone (LH) and follicle stimulating hormone (FSH)
• Immune system: Lack of sleep is believed to weaken the immune system, making us more vulnerable to a range of illnesses from the common cold to more serious conditions such as cancer. Restorative powers are also affected; one study showed wound healing was slowed by lack of sleep(Ref. 5).
• Cardiovascular: There is now evidence to suggest sleep deprivation may be connected to cardiovascular conditions such as high blood pressure and stroke

Many medical conditions affect our sleep, e.g. psychiatric and neurological disorders including depression, anxiety, Parkinson’s and Alzheimer’s disease are associated with insomnia, although there is no currently defined causal relationship.

PHYSIOLOGY OF SLEEP
Our sleeping patterns (or body clocks) are governed by two mechanisms:

• Homeostasis – is the physiological process by which various internal body systems, such as blood pressure and bodytemperature, are kept in a ‘steady state’ and thereby controls the amount of sleep we need.
• Circadian rhythm – describes the cyclical changes in the body over a 24-hour period. In humans this is set by the brain’s ‘clock’, a region known as the suprachiasmatic nucleus (SCN), and is very sensitive to the hormone melatonin. The circadian rhythm governs the time period when we sleep, when we wake and feel naturally ready to do so. Disruption of the circadian rhythms affects being able to get to sleep, sleep quality and ease of waking up.

Sleep and wakefulness are controlled via the brain, where a fine balance between the hormones that promote arousal and sleep is regulated. Melatonin is an important, naturally occurring sleep promoting hormone. It signals night and day, is released by the pineal gland when the retina detects less light (darkening) and so levels naturally rise in the evening and are lower during daylight hours. It plays a role in regulating the circadian rhythm and has a strong association with sleep.

QUALITY AND QUANTITY OF SLEEP
The optimal amount of sleep we should have each night varies from individual to individual. The body’s natural method of regulating how much sleep we need is set by our natural circadian rhythms, although when these become disrupted, the quantity and quality of sleep achieved can be affected, making an impact on our health and daytime functioning. Some clinical studies suggest that sleep quality rather than quantity has a greater impact on quality of life and daytime functioning(Ref. 6).

SLEEP HYGIENE
If you are having difficulty sleeping, the first step should be to review lifestyle and bedtime habits to promote regular and satisfying sleep patterns, bearing in mind that good sleep habits start during the day. Some useful tips include:

• Maintain a comfortable bedroom environment. Ensure your bedroom is quiet, at a moderate temperature and that your mattress offers good support
• Exercise on a regular basis. Some gentle exercise, preferably outdoors, may help you to rest later that night
• Relaxation techniques such as breathing exercises or aromatherapy help some people. Try also to set aside the bedroom as a sleep-dedicated zone and avoid watching television, eating, working or even reading in bed
• Set regular sleep and wake times so that you are sticking to the same routine every day, even if you don’t feel like it
• Avoid stimulants, such as alcohol, coffee and nicotine, especially close to bed time, and don’t eat heavy meals late in the evening

However if your problems continue, seek professional advice from your doctor or other healthcare professional, as there are psychological and pharmacological treatments that may help.

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1. Royal College of Psychiatrists (www.rcpsych.ac.uk) – Sleeping Well. Accessed 10.04.08 at http://www.rcpsych.ac.uk/mentalhealthinformation/mentalhealthproblems/sleepproblems/sleepingwell.aspx

2. Young, E. Sleep Tight. New Scientist 15.03.08

3. Taheri S Lin L, Austin D et al. Short sleep duration is associated with elevated ghrelin, reduced leptin and increased body mass index. PLoS Med 2004; 1(3): e62

4. Gottlieb DJ, Punjabi, NM, Newman AB et al. Association of sleep time with diabetes mellitus and impaired glucose tolerance. Arch Intern Med 2005; 165(8): 863-7

5. Gumustekin K, Seven B, Karabulut N et al. Effects of sleep deprivation, nicotine, and selenium on wound healing in rats Neuroscience 2004; 114: 1433-1442

6. Kandel ER, Schwartz JH, Jessell TM. Principles of neural science. © The McGraw-Hill Companies Inc, 2000

7. Wade AG, Ford I, Crawford G et al. Efficacy of prolonged release melatonin in insomnia patient aged 55-80years: quality of sleep and next-day alertness outcomes. Curr Med Res Opin 2007; 23(10): 2597-2605

8. Wade AG, Zisapel N, Lemoine P. Prolonged-release melatonin for the treatment of insomnia: targeting quality of sleep and morning alertness. Ageing Health 2008; 4(1): 11-12