Why Is Sleep Important? What Happens While You Sleep
Why is sleep important? What sleep does for your brain, memory, immunity, heart and appetite, how many hours you need, and why an early night helps.
We spend about a third of our lives asleep, so sleep can look like wasted time. Why is sleep important, then? It is when the brain stores memories and clears waste, the body repairs, immunity recharges, appetite hormones reset and blood pressure falls. Adults need at least 7 hours.
This guide explains what happens to your body and brain every night, with figures from published studies.
Why do we need sleep?
For years people assumed sleep was simply a pause, the body switching off like a machine. Modern research shows the opposite: sleep is an active state in which the brain and body do work that cannot be done while we are awake.
Professor Ahmed BaHammam, a professor of sleep medicine in Saudi Arabia, describes sleep as an active state in which the brain clears the toxins that built up while awake, and in which the body and memory recover.
Science has not settled every answer to why we need sleep. But what we already know is enough to show that sleep is not a luxury. It is a basic need, like food and water.
Sleeping enough hours but still waking up tired?
If your sleep doesn't refresh you despite enough hours, a sleep disorder such as sleep apnea or insomnia may be the cause. A sleep medicine consultant can help you find out.
Book a sleep disorders consultation
Living outside Riyadh? Book an online sleep consultation
What happens to your body during sleep?
To understand why sleep is important, it helps to know that sleep is not one solid block. It runs in cycles that repeat 4 to 6 times a night, each lasting about 90 minutes on average. Each cycle has two main types of sleep:
Non-REM sleep: about 75% of sleep, including light sleep and deep sleep. Deep sleep is concentrated in the first half of the night, when the body rests and repairs tissue.
REM sleep: about 25% of adult sleep, when most dreaming happens. It gets longer in the second half of the night.
Each stage has a different job, so cutting sleep short or breaking it up takes away some of these jobs, even if you get a few unbroken hours.
Sleep and the brain: memory and clearing waste
Some of the clearest answers to why sleep is important come from the brain:
Locking in memories
During sleep, the brain moves what you learned during the day into long-term memory. Harvard Medical School notes that non-REM sleep supports remembering facts and information, while REM sleep supports learning skills. That is why a student remembers more after a good night's sleep than after staying up late.
Clearing waste from the brain
In a 2013 study in mice published in Science, the spaces between brain cells widened by about 60% during sleep, so waste was cleared faster, including beta-amyloid, a protein linked to Alzheimer's disease. This is called the glymphatic system, and it works more efficiently during sleep.
To learn what happens to the brain and focus when sleep runs short, read our article on the effects of sleep deprivation on the brain and nerves.
Why sleep is important for your body
The benefits of sleep go beyond the brain and reach every system in the body:
Tissue repair and growth
Growth hormone release is linked to deep sleep, as research published in the Journal of Clinical Investigation has shown. That is why children and teenagers need more sleep, and why athletes need good sleep for their muscles to recover.
A stronger immune system
In a Carnegie Mellon University study, 164 volunteers were exposed to a cold virus, and those who slept less than 6 hours were about four times more likely to catch the cold. In another study on the hepatitis B vaccine, people who slept less than 6 hours had a clearly weaker response to the vaccine.
Appetite and weight
In a University of Chicago study, 12 men slept only 4 hours for two nights. Their fullness hormone (leptin) fell by 18%, their hunger hormone (ghrelin) rose by 28%, and their appetite went up by about 24%. This helps explain why sleep-deprived people crave sugary and fatty foods.
Protecting the heart
Blood pressure falls during normal sleep, giving the heart and blood vessels a rest. That is why the American Heart Association added sleep in 2022 to its list of core measures of heart health, alongside diet, activity, blood pressure and blood sugar.
Why is sleep important for mood and mental health?
Ever noticed that you snap more easily after a bad night? That's no coincidence. In a UC Berkeley study, the amygdala, the brain's emotional centre, became more than 60% more reactive after 35 hours without sleep.
The link works both ways: poor sleep increases anxiety and stress, and anxiety makes sleep harder. That is why treating insomnia is an important part of caring for mental health, and one more reason why sleep is important in everyday life.
How much sleep do you need?
Sleep needs change with age. The American Academy of Sleep Medicine recommends:
4 to 12 months: 12 to 16 hours
1 to 2 years: 11 to 14 hours
3 to 5 years: 10 to 13 hours
6 to 12 years: 9 to 12 hours
13 to 18 years: 8 to 10 hours
Adults: 7 hours or more
Even knowing why sleep is important, many people fall short. In a Saudi study of more than 2,000 adults in Riyadh, 33.8% slept less than 7 hours, and average sleep was only 6.4 hours.
For details for every age, read our article on normal sleep hours by age.
Benefits of going to bed early
Timing is another part of the answer to why is sleep important: it is not only the number of hours that matters. In a UK study that followed more than 88,000 people for about six years, heart disease was lowest in people who fell asleep between 10 and 11 p.m. Risk was about 25% higher in those who fell asleep after midnight.
Other benefits of an earlier bedtime:
It fits the body clock, which is set by light and darkness
It gives you more deep sleep early in the night
It makes waking early easier, without an alarm or grogginess
It cuts down late-night screen time and late eating
But this is an association study, and it does not mean someone who sleeps at 11:30 p.m. is at risk. What matters most is a regular bedtime and enough hours.
Sleep and safety at work
One practical reason why sleep is important is that drowsiness slows reaction time and weakens attention, raising the risk of accidents. This matters especially for drivers, pilots and shift workers, where a small mistake can cost a lot.
That is why airlines and transport companies take their employees' sleep seriously: enough sleep is part of safety, not just personal comfort. To learn about the causes of drowsy driving and how to prevent it, read our article on the causes of falling asleep while driving.
What happens when you don't get enough sleep?
When we ignore why sleep is important, the effects show up quickly. The US Centers for Disease Control and Prevention reports that more than a third of American adults don't get enough sleep, and links this with obesity, diabetes, high blood pressure, heart disease, stroke and mental distress.
In the short term, lack of sleep shows up as:
Poor focus and forgetfulness
Irritability and mood swings
More cravings for sugary foods
Catching colds more often
Daytime sleepiness and slower reactions
When is tiredness a sign of a sleep disorder?
Knowing why is sleep important matters less than knowing why your own sleep isn't working. Sometimes the problem is not the number of hours but the quality of the sleep itself. An assessment is advisable if you notice:
Severe daytime sleepiness, or dozing off while driving
Waking up tired despite sleeping 7 hours or more
Loud snoring or breathing pauses noticed by your bed partner
Trouble falling asleep or frequent waking three nights a week for more than a month
Uncomfortable leg sensations that keep you awake
Your sleep doesn't refresh you, whatever you try?
A home sleep apnea test checks for sleep apnea in your own bed within Riyadh. And if the problem is insomnia, CBT-I sessions can help without medicines.
Or book CBT-I sessions for insomnia
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How to get better sleep
Now that you know why sleep is important, these simple steps help you get it:
Keep the same bedtime and wake time every day, including weekends.
Get daylight in the morning, and dim the lights in the evening.
Put screens away at least half an hour before bed.
Avoid caffeine after mid-afternoon.
Keep the bedroom dark, quiet and comfortably cool.
Avoid heavy meals for two to three hours before bed.
If you can't fall asleep within about 20 minutes, get up for something calm, then go back.
Why Subat Clinics?
If you know why sleep is important but can't get enough of it, the next step is finding out what is stopping you. At Subat Clinics you will find:
A consultant in sleep medicine to diagnose insomnia, sleep apnea and body-clock disorders
Home sleep studies within Riyadh, both basic and advanced with EEG
CBT-I sessions with a dedicated specialist
Online consultations for patients outside Riyadh
How to prepare for your appointment
These details help the doctor assess your sleep and find out why it isn't giving you what you need:
A two-week sleep diary: bedtime, wake time and number of awakenings
How you feel on waking and during the day
Notes from your bed partner about snoring or breathing pauses
How much coffee and other stimulants you have, and when
The medicines you take
Your type of work and working hours
Conclusion
Why is sleep important? Because it is when the brain locks in memories and clears waste, the body repairs tissue, immunity grows stronger, appetite hormones reset, and the heart rests. Adults need at least 7 hours, ideally at a regular, early-enough time. If you sleep enough hours and still don't feel rested, there may be a sleep disorder worth assessing.
Book your appointment
Good sleep is not a luxury. If your sleep doesn't refresh you, book now and start by finding the cause.
Choose the service that suits you and book directly:
Address: Othman Ibn Affan Road, Al-Taawun District, Riyadh 12477
Phone: 0112011100
WhatsApp: 0505999713
The clinic is not an emergency facility. In an emergency call 997 or go to the nearest hospital.
Sources
Ajel — Prof. BaHammam on the causes and risks of sleep loss (Arabic)
Harvard Health — How does sleep support memory and learning?
Carnegie Mellon University — Sleep and catching a cold (Sleep 2015)
University of Chicago — Sleep loss and appetite hormones (Annals of Internal Medicine 2004)
UC Berkeley — Sleep loss and the emotional brain (Current Biology 2007)
American Academy of Sleep Medicine — How much sleep do I really need?
Ahmed et al. — Sleep duration among adults in Riyadh (Saudi Medical Journal 2017)
This content is for health awareness and does not replace a personal medical consultation.
Medically reviewed by: Dr. Ahmed Alruhaimi, Consultant in Pulmonary Medicine and Sleep Medicine, Subat Clinics
Last reviewed: October 2026
Frequently asked questions
Can I catch up on sleep at the weekend?
Extra sleep at the weekend may ease tiredness for a while, but it doesn't make up for weeks of short sleep, and it can unsettle your body clock so it is harder to sleep at the start of the week.
Is it better to sleep in the dark?
Yes. Darkness helps the brain release melatonin, and light in the room can break up and lighten sleep.
Do older adults need less sleep?
They need roughly the same hours, but their sleep becomes lighter and more broken, so some feel they sleep less.
Are naps good for you?
A short nap of 20 to 30 minutes early in the day may improve alertness, but it doesn't replace night-time sleep, and long or late naps can delay sleep at night.