Sleep: The secret to sleeping well and waking refreshed. Prof. Idzikowski Chris

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СКАЧАТЬ night-time secretion of melatonin, the hormone that signals the onset of darkness (see page 16), thus preventing or disrupting sleep. (When it is dark, melatonin secretion rises and peaks at the darkest time and then goes down until dawn, when the biological clock is reset to wake.) The effects of blue light are unconscious.

      There are also conscious effects of perceived light: the brighter the light in your bedroom, the more alert and less sleepy you will feel. Taking lux as a measurement of light intensity (see the table below), normal indoor lighting measures around 200 ‘lux’, while a cloudy day is around 10,000 ‘lux’ – significantly lighter, which makes it crucial to block it out as much as possible when you go to sleep. If you cannot control the amount of light you are exposed to and don’t want to hide your eyes with a pillow, consider using an eye mask.

      did you know?

       Blind or visually impaired people have no internal bodyclocks because their retinas are so damaged that light cannot enter the brain. They will therefore have no natural sense of when to get up and when to go to bed.

      In recent years, street and industrial lighting has increased dramatically, which has had a great impact on normal daylight hours and in some people can have the effect of disturbing the timing of their internal clocks. Again, an eye mask, thick curtains, or curtains with extra lining may help.

      The relative intensity of different forms of light

Illuminance	Example
0.00005 lux	Starlight
1 lux	Moonlight
400 lux	A brightly lit office
400 lux	Sunrise or sunset on a clear day.
1000 lux	Typical TV studio lighting
32,000 lux	Sunlight on an average day (min.)
100,000 lux	Sunlight on an average day (max.)

      Note: Lux is a measure of the intensity of light.

      must know

       Decibels

       Noise is measured in decibels (dB). A 3dB change is detectable but because of the scale used with decibels an increase of 3 means that the noise level has actually doubled.

      There is some evidence to suggest that using coloured lighting may affect the ‘colour temperature’ of a room. Colours can be pleasing to some people and irritating for others so it is important not to be too assertive as to which are best. However, in general the warmer colours of sunset tend to be associated with deep sleep while the cooler colours of dawn are associated with darkness.

      Humidity

      One of the most common breathing-related sleeping disorders is asthma, which is often caused by allergens found in the faeces of house dust mites. The relative humidity of your surroundings will be the key factor that influences the prevalence of these mites, which can live in conditions where there is no liquid to drink as they can extract sufficient water from the environment if the humidity is high enough. Surveys in temperate climates show that mite prevalence varies according to seasonal fluctuations in indoor humidity. Mites are absent or rare in homes in dry climates unless use of evaporative coolers adds the moisture to the air that is necessary for their survival. Maintaining average daily indoor humidity below 50 per cent will prevent mite population growth and subsequent sleep-disrupting allergens. Even if humidity is lowered, it can take several months for all the allergens to disappear, however.

      Noise

      People can be awoken by neutral sounds louder than 45 decibels (dB), the equivalent to someone talking quietly (a lawnmower is around 105dB and the threshold for injury to the ear is around 140dB). However, sounds as low as 20dB (below the hearing threshold) can prevent you from falling asleep.

      Conversely, continuous background sounds can be soporific and it seems that sounds even below 20dB can induce sleepiness – a clear danger for lorry and train drivers. Irregular high-frequency noise can have the opposite effect and be intrusive.

      Noise table

Type of noise	Decibels (dB)
Faintest, audible sounds	0.2-20
TV sound studio, quiet library	20-30
Quiet office	40-50
Conversation	50-60
Primary school classroom, loud radio	60-70
Power drill	85-90
Road drill	100-110
Chainsaw	110-115
Jet aircraft taking off, 25 miles away	140

      must know

       Vibrations

       Vibration can affect sleep just as much as noise. It has been found that even quiet traffic noise of 50dB, when accompanied by vibrations, is more disturbing than when there is just noise. REM sleep is more affected than other stages of sleep. Performance the following day can be impaired.

      Noise is a problem in many hospitals, particularly in intensive care units. Research has shown that noise in the latter does disturb sleep, and it could be argued that healing processes could be facilitated if natural sleep were promoted. Studies have shown that in neonatal intensive care units, for example, very low birth weight babies sleep more deeply and cry less if quiet hours are introduced. Playing ocean sounds to mask the noise in an intensive care unit has been found to work.

      In controlled studies, traffic noise has been shown to increase the time it takes to get to sleep and to lead to greater irritability. Aircraft noise from airports can affect EEG results, showing lighter sleep. However, despite the fact that higher psychiatric hospital admission rates, GP visits and self-reported health problems have been reported near airports, the effects are highly variable from individual to individual, some being oblivious to the noise levels, others not.

      Installing double- or triple-glazing in your home may help, as will wearing ear-plugs, though there is an obvious danger with the latter of possibly life-saving alarms not being heard.

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