Why do we sleep? The science behind our need for rest

At a glance

• Sleep, like ageing, is an inescapable consequence of something called ‘aerobic metabolism’.
• Just 24 hours with no sleep has a short-term health consequence, however, prolonged sleep deprivation can have a negative health impact on our mental, physical and emotional health.
• Adults who sleep fewer than six hours a night have a 20% higher premature death compared with those who sleep seven to eight hours.
• REM sleep is an important stage of sleep, contributing to creative thinking and processing our emotions.

Why do we sleep – and what does new research suggest?

We all need sleep. Yet, the reasons for it and what actually happens in the land of nod still remain a mystery to many.

One group of researchers, however, have moved one step closer to understanding it.

According to a recent study, sleep, like ageing, is an inescapable consequence of something called ‘aerobic metabolism’ – the biological process which our cells use to generate energy.

When our brain detects a build-up of these electrical signals, this triggers us to need to sleep.

Essentially, what this research helps provide is a new explanation for why we sleep, and this, in turn, is encouraging scientists to re-think the entire role it is having in maintaining our bodies’ functionality.

What does sleep do for the brain and body?

What all scientists agree on is that sleep – in all its forms – is extremely good for us.

This – seemingly – simple act helps us to repair and restore our mind and body, consolidates our memories and even clears waste products from the brain.

Not having enough of it, meanwhile, can be very bad for us.

“Large numbers of adults report persistent sleep problems yet rarely link these to long-term disease risk. Many accept poor sleep as ‘normal’ ageing or work stress.”

– Dr Marie Edison, Head of Medical Policy, Vitality

Just 24 hours with no sleep can cause short-term consequences – and prolonged sleep deprivation can impact our mental, physical and emotional health.

So, are we really taking our nightly journey into this mysterious land, where we spend one-third of our lives, seriously enough?

And what steps can we all take to ensure we’re getting the Zs we deserve?

• The fundamentals of sleep | Magazine | Vitality

What happens when we lose sleep?

Sleep patterns are something Vitality’s Head of Medical Policy, Dr Marie Edison, believes are too-often overlooked by public and medical professionals.

Often, if we have a health concern, we’re not asked about our sleep patterns as much as our exercise regimes or if we have a healthy diet.

“Irregular sleep duration and timing have been associated with increased cardiovascular risk, independent of sleep quantity and quality,” says Edison.

“Large numbers of adults report persistent sleep problems yet rarely link these to long-term disease risk. Many accept poor sleep as ‘normal’ ageing or work stress.”

She is, however, positive about the fact that sleep is “gradually being reframed alongside diet and exercise as a key pillar of cardiometabolic and brain-health strategy.”

Vitality’s own data has found that adults who sleep fewer than six hours a night face a 20% higher risk of premature death compared with those who sleep seven to eight hours[1].

A lack of sleep also impacts how we process food.

The study reported that people were less satisfied after eating if they had restricted sleep; and just one week of reduced sleep can impair glucose control to that of a pre-diabetic[2].

Our cognitive performance is also bound by how well we sleep.

“A single night of curtailed rest slows reaction times, weakens attention and erodes memory; extended restriction produces impairments comparable to alcohol intoxication,” the report said.

Similarly, if we cut our sleep short “the result is not only forgetfulness but also reduced creativity and poorer problem-solving”.

Lara Aillon-Sohl, a psychiatrist at Vitality partner Headspace, likens sleep to the “single most important thing that we can do to reset the health of our brains and body each day.”

“Poor sleep or insufficient sleep leads to changes on the cellular level resulting in an increase in inflammation, hormone dysregulation, disruption of our metabolism, and cellular damage.

“As a result, we see an increase in morbidity for diseases such as obesity, diabetes, cardiovascular disease, cancer, dementia, depression and anxiety.”

No wonder Albert Einstein boasted about getting 10 hours of sleep a night.

• Is power napping worth it? | Magazine | Vitality

What’s the difference between REM and Non-REM sleep – and why does it matter?

Aillon-Sohl explains how the two phases of sleep (REM and non-REM) play different roles in our bodies’ natural processes.

“Non-REM sleep is noted for influencing hormones such as human growth hormones,” she says.

Meanwhile, REM sleep, where 80% of dreams occur “is thought to be a time of processing our emotions and contributes to creative thinking,” adds Aillon-Sohl.

“Appropriate duration and timing of REM sleep is connected to enhanced learning and memory, faster cognitive processing and greater extinguishment of fear and anxiety.”

Waking up to the ways in which our sleep impacts our health is therefore no bad thing.

Understanding how we can make, potentially small, adjustments to our sleep patterns could have a major impact on our overall health.

“Most people know that their performance and quality of life is connected to a good night’s sleep, and they want to know how to improve and maximise their sleep opportunities to supercharge their wellbeing,” explains Aillon-Sohl.

Is sleep quality more important than sleep quantity?

Edison says that all this is leading to a cultural shift.

The question health professionals and research are starting to ask is no longer ‘how many hours did you sleep?’ but ‘how well did you sleep?’”

One of the best ways to ensure that we are achieving our sleep goals is through smartwatches and devices.

Smartwatch brand and Vitality partner, Garmin, for example, offers an ecosystem of sleep metrics to help people get to know their sleep patterns better.

This includes a sleep score, sleep stages and body battery.

According to Garmin, “being able to track sleep patterns allows users to build a great awareness and understanding of it, and how to improve it day to day to help achieve better wellness and performance in waking hours.

“Through our features, like Sleep Coach (which provides users with their personalised sleep-need recommendation), we’re moving sleep from the ‘I’ll just go to bed’ mindset to ‘I’ll plan for my best sleep’ mindset.”

Consistently tracking our sleep in this way helps support small and repeated behaviours that can help to build healthier sleeping habits.

“My hope is that these technologies will provide support and guidance that is grounded in scientific evidence and leads to meaningful improvement in sleep and quality of life,” concludes Aillon-Sohl.

So, try not to take your sleep for granted. It can do far more for our physical and cognitive function than we tend to give it credit for.

Expecting a new theory of relativity to come to you in your dreams might be a step too far, though.

What can you do tonight to sleep better?

Darken down

Reduce light levels in your home, switch on blue light filters and turn down the brightness of your devices at least two hours before bed. This helps to trigger the release of melatonin, the sleep promoting hormone.

Gentle stretch

Ease any physical discomfort or pain before bed with some gentle stretching. Increase the chance of you doing it by placing a yoga mat in the bedroom.

Adopt calming activities

Mentally calm down by engaging in relaxing activities such as reading, listening to music or drawing. Equally, aim to switch off digital devices 30-60mins before bed and keep them out of the bedroom. The reduced mental, emotional and light stimulation will help you to fall to sleep more quickly.

Be grateful

Having gratitude can be as easy as spending a few minutes at the end of the day in bed to think about the events, people or places that you’re grateful for in your life that day. Whatever comes to mind, see if you can clearly identify why it is that you are grateful for it and pause to notice how being appreciative feels.­

[1] Building healthy sleep habits – The next frontier in prevention, Vitality & London School of Economics, 2025

[2] Building healthy sleep habits – The next frontier in prevention, Vitality & London School of Economics, 2025

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