Sleep? Death - like condition?
For a long period of time, we considered sleep to be a death-like condition. This idea dates back to ancient Greeks who believed the god of sleep – Hypnos, and death god - Thanatos, are brothers. At the beginning of the 20th century, after development of electroencephalogram (EEG - records brain waves), science showed that sleep and death have nothing in common. Nowadays, we know that some brain areas are even more active during sleep than when we are awake. Three key questions are: how we sleep, how much is enough, and why we sleep in the first place.
Three key questions are:
- How we sleep?
- How much is enough?
- Why we sleep in the first place?
HOW WE SLEEP?
Sleep phases - sleep architecture
Sleep is anything but an amorphous, static state: as we sleep, we go through several sleep stages. In total, 5 sleep stages have been recognized which behave as differently to each other as sleeping and exercising.
- Stage W (awake)
- Stage N1 - Transient Light Sleep
(Non-Rapid Eye Movement 1: NREM 1)
- Stage N2 - Stable light sleep (NREM 2)
- Stage N3 - Deep Sleep (NREM 3 + NREM 4)
- Stage R - Remnant or Dream Sleep (REM)
"Non Rapid Eye Movement" literally means "no quick eye movements". This stage is understood as a counterpart to the "stage R", the so-called dream or REM sleep, which is characterized by rapid eye movements. It used to be thought that the rapid eye movements during REM sleep resulted from the pursuit of dream images. Today this theory is doubted.
Together, the sleep stages form an approximately 70 to 110-minute cycle, which repeats during night up to five times, and is called the "sleep architecture". The composition of the cycles varies over the course of the night: for example, deep sleep, which accounts for approximately 15-20% of total sleep time in healthy people, is usually limited to the first half of the night. At the same time light sleep phases are increasing. Overall, they account for about 50% of the night time sleep.
The sleep architecture is highly individualized and is determined in the sleep laboratory by means of so-called polysomnography. Polysomnography records, among other things, whether and how often the patients go through the individual sleep stages.
Sleep internal clock
Every day we are exposed to the so-called circadian rhythm which tells us when to rest every 24 hours. It is an internal clock of the brain which conducts signals and stimulates the organs to high performance or force them to rest. The internal clock dictates its own rules so we cannot freely exchange our activity and sleep phases. For the most part our alertness is coupled with brightness, our drowsiness with darkness. This is why sleep is less restful during the day and working is harder for us at night.
This internal clock also dictates are we in the group of morning or evening types. This has little to do with lack of discipline or endurance. Responsible are the genes. In our society, we find twice as often morning as evening types. However, most of the group belong to the mixed types. In the course of life, the circadian rhythm may shift forward: in older we are more likely to encounter morning types - and at younger age, the higher the likelihood of finding late types.
HOW MUCH WE SLEEP?
Morning or evening types?
Our internal clock dictates are we in the group of morning or evening types. This has little to do with lack of discipline or endurance. Responsible are the genes. In our society, we find twice as often morning as evening types. However, most of the group belong to the mixed types. In the course of life, the circadian rhythm may shift forward: in older we are more likely to encounter morning types - and at younger age, the higher the likelihood of finding late types.
Short vs long type sleeper?
From a purely statistical point of view, average person needs around seven hours of sleep. Whether we are short-or long-sleeper, is determined by many factors, and is hardly a performance or will question.
One factor is genetic programming similar to morning and evening types. Compared to other mammals, humans are in the middle of sleep when it comes to sleeping: elephant sleeps for a maximum of four hours; bats up to 20 hours a day.
Whether sex is addition factor is controversial. Based to some studies, women sleep longer than men (9.8 vs. 8.4 hours), however the cause is yet to be determined. However, what is certain is that our need for sleep is different in seasons: in winter, we usually crave more sleep than in summer. People who live in regions with distinct seasonal changes sleep up to two hours longer in the winter.
Very important factors are, stress and illnesses, which influence our sleep behaviour.
What is certain is that our need for sleep is not a lifelong continuum and is influenced by our age: Babies need 16 to 18 hours of sleep a day. Many a senior barely six.
How many hours each one truly needs is not be a question of statistics, but of personal wellbeing. Sleep requirement in the mirror of season, gender, age, stress….
WHY WE SLEEP?
Sleep is the essence of life
Although the mystery of sleep and its (restorative) functions still have to be clarified, it is clear that sleep is important in maintaining physical and mental health. Sleep is linked with the cardiovascular, immunological and endocrinological system. Today we do know that during sleep our body releases hormones, which are important for maintaining homeostasis of these multiple systems like. During sleep, harmful substances are removed from the brain and memory consolidation takes place.
However, even with all the research being done in last 100 years, still it has been extremely difficult to give a complete answer to why we need sleep for these function to take place?
That is why research was concentrated on the reverse question: What happens if we do not sleep or sleep too little?
Lack of sleep makes us sick?
The sleep deprivation research showed repeatedly that we harm our organism significantly if we allow it too little sleep. Subjects that slept one to two hours less than usual, even after few days quickly experienced massive changes in their attention, responsiveness, memory, hormone balance, immune system, and mood.
Several studies suggest a connection between continuous sleep deprivation and common diseases such as high blood pressure, obesity, diabetes mellitus, Alzheimer's disease, gastritis, burnout syndrome, and higher mortality.
In addition, around one third of all car accidents or one quarter of all fatal accidents are attributable to a lack of sleep.
Healthy sleep as a new life style of the 21th century
Each year we invest enormous amount of money and time in different fitness, wellness and anti-aging procedures and products. At the same time, we sleep less and less, and ignore studies that revealed it as a key health and free anti-aging factor. We could argue that our 24/7 oriented society denigrates sleep. Who sleeps a lot, is considered lethargic? Who suppresses his natural need for sleep, as agile? Researchers have calculated that in the last century the average duration of sleep in Europe shortened by an impressive two hours.
We need to change our life style. To stay healthy in the long term, we need 6 to 9 hours of healthy sleep every day, depending on your individual need for sleep. If you doubt your personal sleep requirement, you should seek sleep medical advice.
They will take care of you
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PETER JFM LOHUIS, MD PHD
BORIS FILIPOVIĆ, MD PHD
BORIS ŠIMUNJAK, MD PHD
MARINA MILOŠEVIĆ, MD
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