Why is sleep important?
One way to explore the answer to this question is to look at what happens when we don’t sleep enough. We can all recognise feeling irritable, tired and struggling to concentrate after a restless night. This gives us clues about some of the functions of sleep, such as replenishing energy stores in our muscles , regulating our emotions, improving memory, focus and concentration.
In 1965, a 17-year old high school student, Randy Gardner, set a World record for staying awake for 264 hours (11 days) straight. He suffered extreme sleepiness, anxiety, panic and even hallucinations. The Guinness Book of World records subsequently refused to accept further attempts to set a record, since they deemed it too dangerous.
Researcher Allan Rechtschaffen conducted sleep deprivation experiments on rats in the 1980s. The rats lived on a rotating disc over a vat of water. When they started to fall asleep, they would fall into the water if they didn’t start moving. Within 4 weeks without sleep, all the rats had died. Some suffered stomach ulcers, some infections, others died of heart attacks and organ failure. It was as if the entire bodily system had gone into overdrive.
Quite simply, we cannot survive for long without sleep. In fact, we can survive for longer without food than we can without sleep. Sleep is the essential price we pay to be able to make the most of our waking hours. When we’re sleep deprived, we’re not firing on all cylinders; our physical health, mental performance and emotional wellbeing all start to suffer.
What happens when we sleep? The stages of sleep
Another way to explore the importance of sleep is to look at what happens in the brain and body while we sleep. Sleep is not one single process. We progress through 4 different stages or types of sleep repeatedly during the night, in a series of cycles.
Sleep stages are defined by different patterns of electrical activity in the brain. Sleep scientists monitor these stages by sticking electrodes onto the scalp during sleep, using a device called an electroencephalogram, or EEG.
The diagram below shows a hypnogram, which is a map of the stages of sleep we go through during a typical night. Every time we pass through all 4 stages of sleep, this is called a sleep cycle - and it takes around 90 to 120 minutes, so we may have 4 or 5 cycles in a typical night.
In this example, the sleeper goes through 5 sleep cycles of progressively deeper and then lighter sleep. In between cycles 2 and 4, they briefly wake up. Brief awakenings during the night can be a normal part of sleep, and are usually nothing to worry about.
What happens in Stage 1 sleep?
Stage 1 sleep is a light transition stage as our consciousness starts to switch off. This is somewhere between daydreaming and sleep. Sometimes people get a sensation of falling during stage 1 sleep, and wake up with a sudden movement, called a hypnagogic or hypnic jerk. Stage 1 usually only lasts 5-10 minutes. This is the kind of sleep you usually get when you press the snooze button. It’s probably better to just set the alarm for when you need to wake up since extra Stage 1 sleep is not thought to be very restorative.
What happens in Stage 2 sleep?
Next is Stage 2 sleep, where we spend around half of the night. Heart and breathing rates slow down, and the body temperature starts to fall. Muscles go through periods of gentle contraction and relaxation. With fewer inputs to process, the brain can get to work and strengthen certain types of memory.
What happens in Stage 3 sleep, or deep sleep?
After about 40 minutes we enter Stage 3 or deep, slow wave sleep. This is the most physically restorative stage of sleep. Blood pressure and stress hormones reach their lowest levels. Deep sleep is when most of our growth hormone is produced. We repair damaged tissues, strengthen bone and muscle. The immune system ramps up its work in fighting infection. Our brain flushes out nasty toxins like beta amyloid and tau which accumulate in Alzheimer’s disease. It’s quite hard to wake someone up from deep sleep, and when you do, they often get ‘sleep inertia’ and wake up groggy and disorientated. As you can see from the hypnogram, we tend to get more deep sleep in the first part of the night.
What happens during REM sleep?
After deep sleep, sleep becomes lighter and we enter REM or Rapid Eye Movement sleep, which is when most dreaming occurs. During this phase of sleep the main muscles that we use to move around are temporarily paralysed but, as the name suggests, our eyes dart backwards and forwards. One theory is that dreams are part of the process of reviewing memories and thoughts from the day in order to slot them into our longer term memory banks, helping us to organise information and solve problems. REM sleep is very important for reducing the intensity of emotional memories.
How can I get a good night’s sleep?
As we get older, we naturally have more breaks between sleep cycles, and sleep gets more fragmented. We spend less time in deep slow wave sleep, and more time awake during the night. This makes sleep less restorative.
Scientists are not entirely sure why sleep changes as we get older, but there are many factors at play, including a weakening of our circadian rhythms (body clocks) and lower production of the hormone, melatonin. Melatonin signals the brain and body to prepare for a deep sleep. In addition, older adults are more likely to suffer from pain, chronic conditions and nocturia (needing the toilet during the night), all of which can have a disruptive effect on sleep.
How can I get more deep sleep, or REM sleep?
I frequently get asked how we can get more deep sleep, especially as we age. In fact, what we need for good quality sleep is a good balance of all stages of sleep. Uninterrupted sleep allows our brains to switch in and out of the stages that we need. On days where you have been very physically active, for example, it’s likely that your brain will prioritise deep sleep, but on particularly emotionally demanding days, it may be that you get more REM sleep in order to process those new experiences.
Top 10 Sleep Promoters
All of the steps below will help to promote good quality sleep, including a healthy amount of deep sleep, and a good balance of light sleep and REM sleep. We can’t control the amount of the different sleep stages that we get - we can simply create the conditions which allow the brain to switch in and out of the sleep which satisfies our unique needs for the day.
- You can only get sufficient good quality sleep if you allow enough time for sleep in general! Adults are recommended to get a minimum of 7 hours of sleep each night for optimal health and daytime function. In order to get 7 hours of sleep, it’s likely that you’ll need to be in bed for 7.5 to 8 hours.
- Melatonin is produced in response to darkness,
so one way you can help to support natural melatonin is to dim the lights
within the last 90 minutes before bed, and to try and make your bedroom as
dark as possible. Using an eye mask has also been shown to promote deep
- Sleep quality improves with consistent sleep
timing. If you aim to wake up and prepare for bed at a similar time each
day, this will strengthen your circadian rhythms, and has been shown to
enhance both deep sleep and REM sleep.
- Our circadian rhythms rely on exposure to
natural daylight to know that it’s time to be active. Aim to get outside
for at least 10 minutes every day within an hour of waking up to kick
start your daily rhythm, and encourage the brain to be ready for sleep 16
- Regular physical activity is one of the best
things you can do to improve your health, and it’s great for sleep too.
People who exercise tend to fall asleep faster, stay asleep for longer and
have more deep sleep.
- In order to get into deep sleep, the body has
to cool by almost 1C. Therefore, sleeping in a room which is slightly
cooler than normal room temperature can help to promote better quality
sleep. Try to avoid having too many covers, and allow air to circulate in
- Alcohol disrupts the quality of your sleep,
leading to more fragmented sleep cycles. If you do decide to drink, you
will have better quality sleep if you stop drinking at least 2 hours
- Stress is another factor that can disrupt deep
sleep. Try to protect at least the last half hour of the day to switch off
and do something enjoyable and relaxing. This might mean quality time with
loved ones, chatting to a friend, reading a book, listening to music or
having a bubble bath.
- Eating late can disrupt the quality of your sleep. If you’re still actively digesting, it will be harder to get into a deep sleep. Try to complete your last main meal 3 hours before getting into bed. If you’re still hungry, try a light healthy snack before bed.
- This one is a bit left field, but have you tried cold water immersion? There is growing interest in wild swimming, cold showers and even ice baths, to promote health. There is some evidence from small studies that cold water immersion helps to improve our balance between the ‘fight or flight’ stress response and ‘rest or digest’ recovery mode. This may help us to fall asleep faster, and have better quality sleep. I’d recommend cold water immersion in the mornings, rather than just before bed, since it can spark an adrenaline fuelled response!