"There are no two people in the world who have the same nights’ sleep twice … Nor is there such a thing as a perfect nights’ sleep: everyone takes a short time to fall asleep and wakes more than one or more times a night … It is how we behave when we can't get to sleep and what we do when we wake that makes us a normal sleeper." ~ Guy Medows, The Sleep Book
What do we mean by a “Good Night’s Sleep”?
Many might think that you haven't slept well unless you have had a solid 8 hours of refreshing sleep, however as the above quote from The Sleep Book indicates, accepting variation is the key to realistic expectations of good sleep.
Variations Affecting Sleep
Sleep patterns across different cultures vary and there is a striking difference between cultures with plentiful sources of artificial light and those without. Pre light cultures go to sleep sooner after sunset and wake several times through the night. This wakefulness can last for several hours, with boundaries between sleeping and waking becoming more blurred.
Many nomadic, hunter gatherer peoples will sleep on and off throughout the day and night for shorter periods depending on what is happening. Although most cultures sleep during the night, in some hot countries people may also sleep during the day when it is impossible to work, becoming more active later in the evening and at night when the temperatures cool. Sleeping with other people and other creatures also varies between cultures. For some communities, sleep is an active social time, depending on sleep groupings, with no constraints on noise or activity.
The advent of artificial light in the mid 19th century significantly shifted our sleep patterns, particularly here in the west. Whilst our ancestors were used to a more broken sleep pattern with a 1st and 2nd sleep period over the course of the night, artificial light has helped eradicate this segmented sleep pattern almost entirely. "The Idea of a first and 2nd sleep has receded entirely from our social consciousness," Historian Roger Ekirch.
Physiologically, sleep timing is controlled by something called the Circadian clock as well as sleep-wake homeostasis. The Circadian clock is our 24 hour inner time-keeper, effecting biological and physiological processes, anticipating environmental changes such as temperature and light, and allowing us to adapt.
How much sleep do we need?
Our sleep requirements vary amongst greatly depending on our age group. A new born child may sleep up to 18 hours a day (although it might not feel this much!) and this need will gradually reduce throughout their life time. In 2015, the National Sleep Foundation of America recommended the following average amount of sleep per age group:
- 14-17 hours for a newborn
- 9-11 hours for a school age child
- 7-9 hours for an adult
- 7-8 hours for an older adult
The amount of time we need to sleep is also regulated by genetics. Our sleep duration is affected by the Gene DEC2. For some, a mutation in this gene means they are genetically wired to need 2 hours less sleep than the average person in their age group. Other factors affecting how much sleep an individual needs include some neurotransmitters, the production of which can be traced to specific genes, and our homeostasis, which also has its own set of genes.
What can upset our sleep patterns?
The Circadian process is thought to counteract the homeostatic drive for sleep during the day and enable it at night. The Circadian clock is particularly important as it influences the ideal timing for the restorative sleep episode through increased secretion of melatonin at night.
Variable sleep patterns, travel (especially across time zones), alarm clocks, TV before bed etc. can all lead to chronic Circadian desynchronisation. This internal clock is profoundly influenced by changes in light. Blue light in particular has strongest effects, leading to concerns about electronic media being used before bed and how this may influence sleep. It is now generally recommended to switch off all electronic devices at least an hour before bed to aid a better night sleep. We are also influenced by aspects of social time, when others are awake, when work is required and the time on the clock. So shift work, family work patterns, social events and clock watching can all effect our sleep drive and therefore the quality of our sleep.
The Importance of Sleep
"Sleep is a mysterious shift in consciousness that our bodies require everyday." ~ Yinka Thomas Msc, Article 'Get a good nights sleep.'
There are many theories about why we sleep but on the whole it is agreed sleep is vital for our functioning. Not only does it conserve energy, it promotes waste clearance from the brain, is restorative for wound healing, strengthens the immune system, restore signaling strength of the synapses, processes memory, preserves us at our most vulnerable period and some research shows sleep clears negative emotions. Certainly lack of sleep has been shown to lead to slower brain waves in the frontal cortex, a shortened attention span, higher anxiety, impaired memory, grouchy moods and variation in weight.
So what is happening when we are sleeping?
Sleep is a naturally re-accruing state of altered consciousness with the inhibition of nearly all voluntary muscles. During sleep heart rate drops, body temperature falls and we experience complex changes in brain activity. Mammalian sleep occurs in repeated periods.
We measure sleep by measuring brain waves, an entire night of measuring this for a normal sleeper shows us that we go through repeated cycles of wakefulness, light, deep and REM (rapid eye movement) throughout a night.
Light sleep is the most common sleep stage accounting for 50% of our sleep. It is the drowsy stage when we start to feel like we are loosing our grasp of the external world and slipping away, before falling into deep sleep.
Deep sleep is considered the most restful sleep. It is when the body grows and repairs and is an essential part of our physiology. It accounts for about 20% of our sleep and is generally achieved with in the first third of the night.
REM sleep occurs later in the night and in the early hours of the morning. During REM the brain is very active, laying down memory and managing emotions from the day. Heart rate, body temperature and breathing become unregulated. Our arousal and oxygen consumption are higher than when the sleeper is awake. It is also thought to be the period of sleep in which we dream. It is much lighter and therefore easy to be woken in this stage. A lack of REM impairs the ability to learn complex tasks. Newborn babies spend almost 9 hours in REM sleep but by the age of 5 this is slightly over 2 hours.
Each cycle lasts up to about 90 minutes and a normal sleeper might experience 4/5 cycles a night and may be completely unaware of the period of awakening.
Awakening allows you to change body position to prevent aches and pains, go to the toilet etc. It is also thought that awakenings are an evolutionary protective mechanism, designed to allow you to sleep and yet still wake at intervals to check for any approaching danger. This is one explanation for experiencing more wakefulness during pregnancy, not only does the woman often need to change position more often, especially at later stages of pregnancy, but she may also feel more protective and sensitive therefore her body’s responses may be encouraging her to check her surrounding more often.
Woman in general are twice as likely to report sleep problems than men according to the National Sleep Foundation. This may in part be down to the fact that hormones have a strong effect on sleep. There are 10 different hormones including melatonin that effect sleep. In particular, the balance of the sex hormones progesterone and oestrogen can disturb sleep, making women more vulnerable at points of change such as just before their period, during pregnancy and at the menopause. Hormonal changes effect sleep and sleep deprivation in turn effect hormone levels which can lead to a vicious cycle of sleeplessness.
Unsurprisingly, disturbed sleep is one of the most commonly and consistently reported changes I’ve witnessed in my work with pregnant ladies. My next post will look at how pregnancy affects a good night’s sleep.
Note from Editor:
A very interesting article was published at the end of January 2017, which you might also find of use: How your sleep patterns could be contributing to your back pain