The Science Of Sleep

Sleep is something many of us find hard. In fact, around a third of adults in western countries struggle with sleep at least once a week. Learning about the science of sleep can give us some ideas to try and make sleep come a little easier.

The Science Of Sleep

Why Do We Need Sleep?

There are lots of different theories when it comes to the ‘why’ of sleep. A combination of these theories is the most likely explanation.

Investigating what happens when we’re sleep-deprived is a good way of identifying the ‘why’ of sleep.

Unfortunately, long-term sleep-deprivation is a risk factor for obesity, type 2 diabetes, high blood pressure, heart disease, strokes, mental illness, poor memory, focus, and concentration, clumsiness, and a weakened immune system. We won’t necessarily experience these things after a short run of broken nights. But it does demonstrate how important sleep is to our overall health.

Cognitively, after a bad night, we might notice our reactions slow down and thoughts become muddled. It’s difficult to think, pay attention, and maintain our mood. One of the explanations for these difficulties is that when we’re sleep-deprived, parts of our brain become inactive while we’re awake.

If our sleep-deprivation becomes chronic, it can be hard to recognise these signs because they become our normal.

What Happens To Our Mind When We Sleep?

When we’re asleep, our brain’s waste-clearance system clears out waste from our central nervous system and toxic by-products that have built up in our brain over the day. This is important because it helps our brain to work well when we’re awake.

Our nerve cells communicate with one another and reorganise. This supports healthy brain function.

Sleep allows our brain to convert information from our working memory (short-term memory) to our longer-term memory. It only does this with information it thinks is needed. Unneeded information is forgotten. This process is a core part of our memory and ability to learn new information.

A well-rested brain finds it easier to learn, remember, problem-solve, be creative, make decisions, focus, and concentrate.

What Happens To Our Body When We Sleep?

While we’re asleep, our body is busy. It repairs muscles, grows tissues, restores energy and synthesises proteins.

Poor sleep can cause weight gain. This is because while we’re asleep, our ‘hunger hormones‘ decrease. If we don’t sleep enough, these hormones can go out of whack. We have increased hunger levels and suppressed ‘full’ feelings, so we might, unknowingly, over-eat.

Insulin is a hormone that controls levels of glucose in our cells. Healthy cells take up glucose (sugar) easily. When we’re asleep, we use less glucose. This helps our body to regulate our overall blood-glucose levels, preventing insulin resistance by keeping our cells healthy.

Some proteins created by our body when we’re asleep are ‘cytokines’. These proteins make antibodies and immune cells, helping our body to fight infection. This is one of the reasons that when we’re stressed or unwell, we need more sleep.

Sleep is important for our heart health, too. Weight gain and insulin resistance are risk factors for heart disease. As is high blood pressure – which is made worse by lack of sleep, because our blood pressure reduces when we’re asleep. Cortisol is a hormone that’s released when we’re awake. High levels of cortisol are a further risk factor for heart disease. Overall, sleep plays a vital part in maintaining a healthy heart.

Sleep And Mood

Sleep affects mood. When tired, we’re quicker to lose patience and become tearful. We struggle to think; making it hard to implement healthy strategies to cope with life’s ups and downs.

While we sleep, areas of our brain that regulate emotions become more active, which helps us to cope with, and process tricky situations. Sleep helps our amygdala, the part of our brain in charge of our ‘fear’ response, to respond in an adaptive and measured way. When we’re sleep-deprived, it tends to overreact. Being well-rested means that we’re better able to cope with tricky situations.

Poor sleep can contribute to the onset and/or progression of poor mental health. It can also be a relapse trigger. Our mental health can affect our sleep, too. During wonky mental health times, we often find it harder to sleep or sleep excessively. Coping with an unwell brain is a tiring business, and we often need more sleep during particularly anxious or ‘low’ times.

Sleep and mood at inextricably intertwined.

How Much Sleep Do We Need?

According to NHS advice, adults need 7-9 hours of sleep a night, children 9-13 and babies/toddlers 12-17. These are only average requirements; we’re all different.

When unwell, we might need more sleep.

Sleep Cycles

We all have an internal body clock running on a 24-hour cycle. It’s called our ‘circadian rhythm’. It makes us feel awake in the morning, and gradually more tired as we go through a day, until the evening when we’re at ‘peak sleepy’.


Adenosine is an organic compound in our brain. It’s part of our ‘sleep drive’ and makes us feel tired. Our brain produces it throughout the day so the later in the day it is, the more adenosine we have, and the more tired we feel. When we sleep, our body breaks it down, so in the morning, we feel less tired again.


Light impacts our circadian rhythm. It’s processed by our ‘suprachiasmatic nucleus’ (a bit of a mouthful!). This is a cluster of nerve cells that live in our hypothalamus; part of our brain. They help our brain to distinguish between day and night.

The morning sun prompts, cortisol, another hormone, to be released. Cortisol gives us energy and helps us to feel alert, awake, and ready to tackle the day ahead.

When it’s dark, our body releases the hormone melatonin, which makes us drowsy. This helps us wind down to bedtime.

The impact of light on our circadian rhythm is one reason to avoid screens near bedtime. Our brain responds to artificial light in a similar way to natural light. Surrounding ourselves with light before we go to bed, can trick our brain into thinking it’s daytime. Low lighting on an evening can help us to get into bedtime mode.

Stages Of Sleep

We go through a four-stage sleep cycle each night. A full cycle lasts 90-120 minutes. We repeat it multiple times a night. The first three stages class as ‘Non-Rapid Eye Movement (NREM) sleep, while the fourth is Rapid Eye Movement (REM) sleep.

Stage 1: This NREM stage lasts for several minutes. Our sleep is light, muscles begin to relax, heart rate and breathing start to slow, eye movements reduce and brain waves slow down.

Stage 2: This NREM stage is, overall, the longest stage. We fall into a deeper sleep, our heart rate and breathing slow, muscles relax further, temperature drops, and eye movements stop. There are moments of high-frequency electrical activity within our brain, but other than that our brain waves continue to slow.

Stage 3: The final NREM stage is initially longer than stage 2, but decreases in length as the night goes on. Our heart rate, breathing, and brain wave activity slow to their lowest level, and our muscles become as relaxed as they can be. It’s also a restorative stage. Our body repairs cells, tissues and muscles, and restores our energy levels.

Stage 4: This is our only REM stage. It gets longer as the night goes on. Our heart rate, blood pressure and breathing all begin to increase again. Though our eyes stay closed, they flit back and forth rapidly. We might dream, though our arms and legs will remain paralysed so we can’t act on our dreams. During this stage, our memories are consolidated. Important things move from our working (short-term) memory to our longer-term memory.

Sleep Problems: Nightmares and Night Terrors

Nightmares and night terrors are often associated with children, but can affect adults, too.

Nightmares are different from night terrors. When experiencing a night terror, we might thrash, wake abruptly and scream, but we’re unlikely to remember it the next day. Nightmares can cause terror, distress and anxiety. We might remember them the next day.

Conditions including migraines, sleep apnoea, fevers, head injury, and restless leg syndrome can increase our likelihood of experiencing nightmares and/or night terrors, as can some antidepressants. Traumatic events can be a risk factor, too.

If we’re regularly experiencing nightmares and/or night terrors, and they’re impacting our life, it would be worth speaking to our GP.

When Should We Go To Bed?

We might have heard the theory ‘an hour of sleep before midnight is worth two after’. Although it’s not as black and white as that, there is some truth in it. Nothing magically happens at midnight, but we do have more REM sleep as the night goes on. This means that if we’re regularly going to bed in the early hours, then we could be missing out on deep, restorative sleep, so we don’t feel as refreshed when we wake up. Exact timing varies from person to person, depending on genetics and physiology. But it’s worth considering an earlier bedtime if we’re feeling tired all the time.

Shift Workers

Ideally, a regular sleep routine can be helpful, but it’s not always possible. For those who work shifts, we sometimes have to sleep during the day or switch between day and night sleeping. It can have a big impact on our mental health.

Though it’s not a perfect situation, there are things we can do that are helpful.

Firstly, it’s important to have at least one day off a week. If we don’t, then it could be a good idea to check in with our line manager or HR representative.

When sleeping during the day, some things that can help include earplugs, blackout blinds or curtains, sticking our phone on silent, asking other house-members not to disturb us, and having a warm shower before we go to bed. When we finish a night shift, coming straight home and hopping into bed can make it easier to get to sleep than if we go home via the supermarket. As can keeping on top of our alcohol and caffeine intake, especially in the hours before we go to bed. Big meals can make it hard to sleep, so planning our meals around our shifts, to avoid big meals just before bed can help.

A ‘wind down’ routine before bed can help us to get into a ‘sleepy space’. We could keep the same routine when sleeping during the day and when sleeping at night.

Lightboxes can help us to feel more ‘awake’. This can be especially helpful when getting ready for a night shift, or if we have a super-early start.

Managing our sleep around shift work, in a way that suits us can take some trial and error. It’s important to listen to our body and to try to find a system that works for us.

Winding Down

Many of us struggle to wind down at night. We know that it’s important to have evening downtime, but knowing the theory and applying it practically to our lives are two different things.

A realistic bedtime is a good start. Setting our bedtime at 8pm when we frequently struggle to get home much before 7pm isn’t realistic. We’ll end up missing it, giving up, and going to bed too late. A sensible (but realistic) bedtime can help us to implement boundaries protecting our sleep time. The regular routine can help our body and mind to recognise ‘sleep time’, too.

Lots of other things affect our ‘sleepiness’. Temperature, light, a comfy bed, using screens, caffeine and tobacco all affect our sleep – they each have an influence on both our physical and mental readiness for bed. Tweaking them to make them work for us, not against us, can take time, but is worth it.

Exercise can help us sleep, but it’s preferable to do it earlier in the day, not just before we go to bed. Some people find weighted blankets calming and helpful. They can help to biologically relax us.

Some foods can help us sleep, too. These include kiwi, tart cherries, malted milk, fatty fish, nut (including nut butters), banana, rice, turkey, dairy, and porridge. We might also like to try a sleepy tea.

Waking Up

Lots of us feel tired and groggy in the morning. Sometimes we’re more tired when we wake up than we were when we went to bed.

There are things we can do to improve our mornings.

The type of alarm we use is a big one. Many of us are guilty of hitting the snooze button time after time, but this can actually be unhelpful. Moving our alarm clock away from our bed, so we have to get up to turn it off can stop the snooze. Some people find dawn-simulator alarm clocks helpful. Others have whizzy bits of technology that wake us at a certain point in our sleep cycle. For those who don’t need to be somewhere at a particular time, we might choose to ditch alarms altogether.

Once out of bed, our blurry-eyed selves often reach for the caffeine. There’s no problem with a morning caffeine hit, but a glass of water first can help us to rehydrate.

Slow stretches or gentle exercise, and a protein-rich breakfast can form a good foundation for the day, too. As can avoiding our phone for a bit and having a consistent routine.

When To Get Some Help

If we’re having lots of problems with excessive tiredness, disturbed sleep, insomnia, exhaustion, fatigue, and persistent tiredness, and it’s having an impact on our life, then it’s worth getting support and checking in with our GP. They should be able to investigate any psychological and/or physical reasons for our tiredness.

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