On average we sleep for one-third of our lives. Nowadays we understand its cyclical pattern and its essential roles for our physical and mental equilibrium. Since the 1960s our lifestyles have reduced the time we sleep on average by an hour-and-half and, according to the INVS, the French national sleep research institute, 40% of the French have sleep problems and 22% suffer from insomnia*, while 30% of 15-19 year olds have a significant sleep deficit**. A few factors to help understand this fundamental requirement in order to retrain and, where necessary, change your behaviour in order to sleep well... whatever your age.
It is through our internal biological clock, modulated by environmental factors, that we are able to sleep at night and stay awake during the day. Another important factor: the release of the sleep hormone, melatonin, once light levels fall. Sleep is also regulated by neurone systems which, depending on whether they are activated or switched off, keep you awake or encourage sleep.
The stages of sleep
Always in the same order and recurring between four and six times each night, sleep cycles consist of a number of stages. We pass from calm wakefulness or falling to sleep to light slow-wave sleep and then to deep slow-wave sleep and on to dream time or REM sleep.
In light slow-wave sleep you enter a state of relaxation. The body puts itself in energy economy and recovery mode from the fatigue caused during waking hours. Melatonin, produced alongside darkness and with a peak at around 2-5 a.m., improves sleep quality, soothes tension, relaxes and even helps to strengthen our immune system and neutralise free radicals.
In deep slow-wave sleep the body regenerates and "repairs" itself The organs, including the brain, function on minimum level where energy consumption drops by 30%; this is when the body secretes the growth hormone which stimulates the production of proteins to maintain the skin, bones and muscles… and prolactin, an immune system stimulant. As for the brain, it repairs its neurones and creates new connections: memory improves, notably spatial and verbal!
In REM sleep low muscle tone and intense brain activity. It is somewhat paradoxical: the body is atonic and the brain very active. The muscles recover. New neurone circuits are explored (to resolve problems?) and dreams commence - essential for us to manage our emotions and psychological stability.
These stages vary in durationin childrenuntil the age of 4: deep sleep (with the precious growth hormone) and REM predominate, significant signs of development, especially neuronal.
A summary of sleep's roles
During sleep the entire metabolism is disrupted. Under the influence of heightened hormonal secretions, cellular renewal and repair takes place, the immune system is strengthened, the appetite is regulated, and neurological recharging occurs…
Elimination activities are also intense: waste and toxins are evacuated, even within the brain*.
Sleep and cognition are inseparable: Information memorised during waking hours is consolidated (if you sleep on a recently acquired task, its memorisation is improved by up to 30%!); new neurone circuits are created.
So it is easy to predict what will happen if you have a sleep deficit or its quality is reduced: cognitive and mental difficulties (lack of attention, effectiveness, motivation and memory, emotional fragility, irritability), immune system weakness, risk of obesity and diabetes…).
* Lulu Xie et al. Science 342, 373 (2013) Sleep Drives Metabolite Clearance from the Adult Brain.
Sleep varies during your lifetime
At birth the average psychological duration of sleep is estimated to be 18 hours, at 3 years old 12 hours, at 10 years old 10 hours, between 13 and 19 years old 9.5 hours and 7.5 hours for adults. However, genetic variability exists from the very youngest ages which confirms the notion of an individual sleep requirement.
With age the biological clock shifts, hormone levels fall… causing sleep fragmentation with night losses compensated for by naps. The duration of light sleep lengthens at the cost of deep sleep.
To establish your own natural sleep profile
Take advantage of a holiday period: go to sleep when you want and get up as soon as you wake up. Take an average of the time you sleep over several days.
The secrets of a good sleep
Some daily recommendations
Day or afternoon
Play sport, get some air.
Ideal room temperature: 18 to 20°C. Avoid intensive sports in the evening, they increase body temperature and keep you awake.
Carry out a routine in order to synchronise the internal clock with regular hours of going to bed and getting up: also favour taking a nap over sleeping in.
Turn down the lights. Eliminate all causes of sleep disruption: noise, light (television, screens, etc.), tobacco, tea, coffee... Plunge the bedroom into darkness.
Put stressful matters out of your mind.
Favour calming activities such as reading and soft music.
Maintain your own bedtime and getting up routine.
Bedtime routines are a good thing: book, bath, removing make-up…
Sleep is also a function of what you eat
The day-night rhythm is regulated by melatonin which is itself synthesised from serotonin. This sleep hormone is vital for getting off to sleep. The production of serotonin depends on the blood concentration of tryptophan, an amino-acid.
A low glycemic index meal high in carbohydrates and low in protein causes a greater concentration of tryptophan and helps it move around the brain. Foods with the highest levels of tryptophan: chick peas, parsley, parmesan, wholegrain rice, gourd seeds, soya, cod, dairy products, walnuts, eggs, pulses, bananas… These foods should be accompanied by dishes based on lentils, quinoa, rice, etc. to help the tryptophan enter the brain.
Dine at least one-and-a-half hours before going to bed (digestion increases body temperature, disrupting sleep).
Restrict fats which slow down digestion and cause fragmented sleep.
Wurtman RJ, Wurtman JJ, et al. Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios. Am J Clin Nutr. 2003 Jan;77(1):128-32. Minet-Ringuet J, Le Ruyet PM, et al. A tryptophan-rich protein diet efficiently restores sleep after food deprivation in the rat. Behav Brain Res. 2004 Jul 9;152(2):335-40.
Plants, minerals and vitamins help you to fall asleep and to enjoy a calm and refreshing sleep.
Hawthorn and lemon balm: their relaxing effects are traditionally used to reduce tension, agitation and irritability in anxious subjects whose sleep is disturbed by thoughts going round in the head.
Hoarhound:reduces nervousness in children and adults, notably those with minor sleeping difficulties.
Magnesium, zinc and iron: these are actively involved in the conversion of tryptophan into serotonin.
Vitamins B3 and B6 are also required for the conversion of tryptophan into serotonin.
Vitamins B6, B9 and B12 are indispensable alongside an amino-acid, methionin, for converting serotonin into melatonin.
For futher information
Le sommeil, le rêve et l’enfant Docteur Marie-Josèphe Challamel, Docteur Marie Thirion Publisher: Albin Michel April 2011
Mieux dormir et vaincre l’insomnie Docteur Joëlle Adrien Publisher: Larousse May 2014