Last weekend we changed to summer time in Austria, which means one less hour of sleep. One hour doesn't seem like much, but still, when you have to get up at 7 o' clock in the morning and your natural body watch tells you it's only 6am (winter time), this one hour is a lot. I felt sleep deprived for pretty much the whole week...
Why is sleep so important and how much do we need?
Did you know that we sleep for more than 24 years in our life? 24 years out of 81 years life expectancy seem like a lot. But are we missing out if we sleep that much? Should we maybe sleep less?
Generally speaking, how much sleep we need is individually different. It is said that men need about 7 to 8 hours on average, women 8 to 9 hours. This rhythm is also called "circadian rhythm". Of course, we adapt to external factors like light, social factors, temperature... or - the one we all know best - our alarm clock. However, more important than the quantity of sleep is the quality. Sleep is a basic human need. So if we try to cut it short in order to have more time for other things, we don't do our body good.
How does our sleep rhythm work?
When we sleep for eight hours, we go through four to five sleep cycles. A sleep cycle consists of four different stages:
1. REM-sleep: REM comes from "rapid eye movement". In this stage, our eyes rapidly and randomly move in high frequency brain waves. This is the stage, our brain waves are similarly active as when we are awake. And it's also the stage were we have vivid dreams. When we fall asleep, we firstly go through the REM-phase. The next stage is N1.
2. N1 is a non-REM sleep. It's the first stage between being awake, going through a first REM-phase and being asleep. It is often referred as somnolence or being drowsy. This is a light form of sleep - we still move a lot, our muscles are still active and we might open our eyes from time to time. Eventually, our breathing incrementally becomes more regular and our heart rate starts to slow down. Sometimes we suddenly twitch in this phase - a last wheeze before we fall into deep sleep. In this phase, we might also still hear parents or friends talking in the other room or the neighbour's music playing but that's the point we don't really care about it anymore. Normally we don't dream in this period. When we wake up during this period we would often believe we never slept at all.
3. It's hard to say where the exact line is between N1 and N2. In N2, sleep takes over control. It's not the deepest sleeping phase (N3) but in this phase our muscle activity decreases more and we stop being conscious and aware of what is happening around us in the outside world.
4. The fourth phase is the deep sleep phase - N3 or "slow-wave sleep" (delta waves). This is when we are even less responsive to the outside world, essentially cut off from the outside and absolutely unaware of any sounds or other stimuli.
From N3 we slip into the REM-phase again from where we might remember our dreams. However, there are studies that we also dream in our deep sleep phase (N3).
What is mostly important is the ratio between the different phases within a cycle. One cycle takes between 80-90 minutes. In a night sleep, N1 should be approximately 5%, N2 45-55%, N3 15-25% and REM-sleep 20-25%. The amount of time we are awake should be under 5%. Is this ratio good, we can also be well rested after a short amount of sleep. Another sign for being well rested is that each sleep cycle gets shorter each time - it means we have "slept enough".
Most important for our recovery and relaxation is the N3 - the deep sleep phase. Even if you tend to sleep only a few hours every night, this stage shouldn't turn out short. Consequences of "a bad night sleep" - we know know how to define this "bad night sleep" - are a decrease in concentration, heavy eyelids and continuous yawning (oh, I know this so well...). Did you know that when you have been awake for 17 hours without drinking a single alcoholic drink, you react like someone who has 0,5 per mille alcohol level?
What did we learn today?
Sleep is not a static but dynamic construct going through the same stages over and over again. While there are basic components like the named stages and the repetitive sequence of them, there is no strict formula for our sleep. In the different cycles, the different stages might vary in their length of time. The ideal situation is when each stages are passed through several times through the night.
I'll soon make more blog posts about how we can measure our sleep quality, how we can improve our awakening and how we can better deal with jet lags and sleep quality abroad.
Stay tuned and ask questions if you have some addressing this topic!
Good night! 😴 😴 😴