The stages of sleep, explained
Most of us understand that sleep is important for our health, but many of us are still in the dark when it comes to the stages of sleep.
The fact is, we don’t just fall into a slumber and sleep through the night in a continuous, linear way. Instead, we experience a series of sleep stages (known as the sleep cycle), which includes everything from REM sleep to deep sleep.
Keen to discover what really goes on while you’re sleeping? Keep scrolling for everything you need to know, to truly understand the importance of those precious zz’s…
The stages of sleep
As sleep expert and Managing Director of Sleep for Health, Dr Carmel Harrington, explains, all sleep is not the same. There are two different types of sleep: Rapid Eye Movement Sleep (or REM sleep) and Non Rapid Eye Movement Sleep (or NREM sleep). Each type of sleep serves a different purpose, but both are essential to our overall health and wellbeing. “In each sleep stage, particular physiological functions are addressed,” says Dr Carmel. “We are replenishing different parts of the brain and body that are critical to our survival.”
“REM sleep, also known as ‘dream sleep’, impacts how well we behave and our cognitive and thinking ability,” says Dr Carmel. It activates our brain activity and promotes learning when we are awake.
NREM sleep, on the other hand, is dreamless sleep. There are three stages of NREM sleep: stage one and two (also known as light sleep), and stage three (also known as deep sleep, or slow wave sleep). “Light sleep helps to refresh our brain, while deep sleep restores our physical health,” explains Dr Carmel. For example, deep sleep is essential in order for us to build muscle.
As well as having different functions, REM and deep sleep also have different features. “Particular brainwaves are active during REM sleep,” says Dr Carmel, with a pattern that is very similar to our awake brains. Our eyelids also flutter (hence the name Rapid Eye Movement Sleep) – although almost all of the rest of our bodies is actually paralysed. “We have evolved to have this as a mechanism to prevent us acting out our dreams,” explains Dr Carmel.
Deep sleep, on the other hand, is characterised by slow brain waves. “This is the time when we are at our most quiescent and quiet,” says Dr Carmel, and “our heart rate slows and our body temperature lowers”. Sleepwalking and sleep talking occur during deep sleep and are more likely to occur if a person is sleep deprived. Unsurprisingly, this is also the stage from which it is most difficult to arise, which means if you’re awoken (for example, by a miss-timed alarm), it is likely you will feel disoriented.
The sleep cycle
Human beings cycle through the sleep stages (wakefulness, light sleep, deep sleep and REM sleep) multiple times during the night. “For adults, the sleep cycle is usually repeated every 90 to 110 minutes,” explains Dr Carmel.
The individual sleep stages last for varying lengths of time throughout the night. “Initially, we experience a longer time period of deep sleep (about 20 per cent of total sleep time) and a shorter time period of light sleep,” says Dr Carmel, but the pattern is reversed during the final third of of the sleep, when REM sleep dominates (about 20 to 25 per cent of total sleep time). It is also normal to be awake for about five per cent of total sleep time, although Dr Carmel says we are unlikely to be able to recall these periods of wakefulness the next morning.
So exactly how much REM and NREM sleep do we need? As Dr Carmel explains, “the amount of total sleep we need varies depending on the individual, but most adults require about seven to nine hours”. The ideal percentage of time spent in each sleep stage is the same for everyone though: 20 per cent deep sleep, and 20 to 25 percent REM sleep.
There are some exceptions to the rule, though. “Children require more REM sleep and more deep sleep, to facilitate growing and learning,” says Dr Carmel, while lactating mothers also need more slow wave sleep.
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How to maximise your sleep
Feeling physically tired during the day, or struggling to concentrate at work? It could be that you aren’t getting enough of the right type of sleep.
To increase mental alertness while awake, Dr Carmel recommends upping your REM sleep. “Learning something, for example through memory games, sudoku, or even learning a language will help improve your REM sleep,” says Dr Carmel. Oh, and in case you were wondering, reading a book doesn’t count – your brain needs to work a bit harder!
Lacking more in physical energy? The expert says exercise can help improve your deep sleep (just make sure you aren’t exercising within three hours of going to bed).
To help you get into a better sleep pattern, Dr Carmel says a sleep app or sleep tracker can also be a worthwhile investment. Most smartphones have a sleep tracking feature, but for more in-depth data, consider using a fitness tracker such as Fitbit Alta HR ($249.95, fitbit.com), which uses your heart rate to measure the time you have spent in light, deep and REM sleep, so you can work towards getting a good balance. beautyheaven also recommends products such as In Essence Sleep Easy Essential Oil Blend, Blackmores Sleep Sound Formula, Swisse Ultiboost Sleep and Lilysilk Silk Sleep Eye Mask to help promote a more restful sleep.
Finally, some good news for those who err on the side of nine (or even ten) hours sleep: There is no such thing as too much sleep. In the absence of an alarm, “we naturally wake when we have had sufficient sleep,” says Dr Carmel. Which means that lying in after the odd late night is not only enjoyable, it’s also necessary for our health!
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