Why Do We Need Sleep?

Sleep is a natural and essential part of our day. As babies, we spend much of our time sleeping, while as adults, we often wish we had more time to sleep. After a busy day, most of us can’t wait to curl up under our cosy duvets and drift off, dreading the inevitable sound of the morning alarm. But why do we crave sleep so much, and what really happens when we close our eyes?

‘A condition of body and mind that typically recurs for several hours every night, in which the eyes are closed, the postural muscles relaxed, the activity of the brain altered, and consciousness of the surroundings practically suspended.’

Oxford Languages

Scientists haven’t yet determined an exact reason why we sleep, but they all agree that our brains and bodies must recharge and repair. While we sleep, our brain clears toxins and keeps everything running smoothly, helping our body function at its best.

While we sleep, our bodies repair and maintain the essential processes that keep us functioning. This includes:

Sleep is also key to keeping our memory sharp. During REM sleep, your brain strengthens, processes the day’s memories, and rids itself of any waste or unnecessary information. The brain also links new memories with old ones, helping you make sense of your experiences.

One of the most widely accepted theories behind why we sleep is the restorative theory. It suggests that sleep is essential for our bodies to repair and recharge. During this time, our cells heal and grow, replenishing energy used up throughout the day. This includes everything from tissue regeneration and muscle recovery to protein synthesis, which is crucial for growth.

Sleep is vital for immune support. Without enough rest, our bodies become more vulnerable to illness and recover more slowly. Research has also shown that microglia, the immune cells that help fight off infections, are most active while we sleep, demonstrating the importance of a good night’s slumber for our health.

Even while we’re dreaming, our brains stay hard at work, working on several other areas to make sure everything keeps running smoothly. During sleep, the brain removes toxins and strengthens the connections between nerve cells. Studies on mice have shown that without enough rest, the brain struggles to repair itself, leaving us more vulnerable to conditions like dementia and schizophrenia, which depend on healthy brain networks.

Our circadian rhythm plays a key role in regulating important hormones like melatonin and cortisol. Naturally, cortisol levels rise as we wake up, helping to energise us for the day ahead. But when sleep is disrupted, this balance is thrown off, resulting in too much cortisol being released throughout the day and affecting other hormones like estrogen and progesterone, present in both males and females. Sleep deprivation can also impact the thyroid and metabolism, explaining those midday chocolate cravings after a sleepless night.

Another great reason to hit snooze is that sleep is essential for keeping your heart healthy. Research shows that getting the recommended 8 hours of rest can reduce the risk of coronary heart disease by helping prevent the build-up of fatty plaques in the blood vessels around the heart. Studies have also found that taking 1-2 naps a week has been linked to a lower chance of serious cardiovascular issues, like heart attacks and strokes.

While there’s no one-size-fits-all answer, experts generally recommend 7-9 hours of sleep for adults. However, factors like age, genetics, and how active you are during the day can all influence your personal sleep needs. To learn more about what impacts how much sleep we really need, including the recommended hours of rest for babies and children, check out our article: how many hours of sleep do we need? Or, use our sleep calculator for a personalised recommendation on how much sleep you should get each night.

Each time we sleep, we go through cycles made up of two key phases: REM and NREM. Both play a vital yet distinct role in the quality of our rest:

• REM Sleep (Rapid Eye Movement): This phase is responsible for processing emotions, strengthening memories, and, of course, dreaming.
• NREM Sleep: Made up of four stages, including deep sleep, NREM is crucial for physical recovery. It’s the phase where your body focuses on repairing cells, promoting growth, and recharging your energy levels.

The amount of REM and NREM sleep we get can depend on the type of sleep cycle we follow. Most of us stick to a monophasic sleep cycle, where we get all our sleep in one night. However, some people, like shift workers, may rely on a biphasic cycle, with sleep broken up into two periods. Want to know more about different sleep cycles and how they impact your rest? Read our article on the different types of sleep cycles.

A range of factors, both internal and external, can impact how long and how well we rest, disrupting the quality of our core sleep. These include our physical and mental health, our sleep environment, our bedtime habits, like going on social media too close to bedtime, and even who we share the bed with. According to our 2024 sleep survey, 37% of people struggling with sleep disturbances cited being too hot as the culprit, with 31% blaming stress and 16% pointing to their partner’s snoring.

If stress and anxiety are keeping you awake, read our tips on how to calm feelings of anxiety for a better night’s sleep. Or, if your partner is constantly hogging the duvet, learn why it might be time for a sleep divorce.

Sleep disorders are medical conditions that affect how much, how well, and when we sleep, often making it difficult to function normally during the day. They’re commonly linked to mental health issues like depression and stress and can be trickier to manage than everyday sleep disturbances. Some common sleep disorders include:

• Insomnia: Difficulty falling and/or staying asleep, resulting in significant sleep deprivation and stress. Learn more about insomnia and how to beat it.
• Sleepwalking: Walking and sitting upright while unconscious during sleep. Discover more about the severity of sleepwalking and possible treatments.
• Sleep apnoea: A medical condition where breathing stops while asleep due to the relaxation of muscles in the respiratory system. Read about the symptoms and causes of sleep apnoea.
• Night sweats: Excessive sweating during the night, often to the point that it wakes you up. Learn more about what causes night sweats and whether they can be stopped.
• Bruxism: Otherwise known as teeth grinding, this condition is commonly associated with stress and anxiety. Find out how to stop grinding your teeth for a better night’s sleep.
• Night terrors: Mostly affecting children, night terrors are more extreme than nightmares and result in physical symptoms and movements, such as shouting or an increased heart rate. Read more about what causes night terrors and how you can stop them.
• Narcolepsy: A brain condition that affects a person’s ability to control when they’re asleep and awake. Symptoms include suddenly falling asleep during the day, known as sleep attacks, and excessive daytime tiredness.

Sleep is so much more than just a time to rest. It’s vital for everything from physical recovery and memory processing to immune support and emotional balance. Getting enough sleep is essential for our health and daily performance.

Whether you’re looking to improve your sleep quality, make mornings more manageable, or even stop oversleeping, the Sleep Matters Club has all the tips and advice you need for better rest.