Depending on their age, a person needs 7–17 hours sleep in every 24 hours. But, just sleeping is not enough. Deep sleep is essential for health and wellbeing. Most adults need around 1.5–2 hours of deep sleep per night.
Sleep happens in stages, and we spend different lengths of time in light and deep sleep. All the stages are important, but they serve different purposes.
Here, learn about the stages of sleep, what deep sleep is, and how much you need.
Here are some
- People go through two types of sleep in each cycle:
- one stage of rapid eye movement (REM) and
- three stages of non-rapid eye movement (NREM)
- NREM is divided into three stages:
- light (N1)
- deep (N2)
- deeper sleep (N3)
- A person cycles through these stages 4–5 times every night.
- The stages cycle in this order: N1, N2, N3, N2, REM.
- Each cycle lasts around 90–110 minutes.
- The first REM stage is short, but as sleep progresses it gets longer compared with NREM.
The table below gives some details about the stages of sleep.
|Stage||REM or non-REM (NREM)||% of sleep||Around how many minutes?||Characteristics|
|Wake/alert||—||—||—||The person is relaxed. This stage lasts from when the eyes are open to when the person becomes drowsy and their eyes close.|
|N1 (NREM stage 1): Lighter sleep||NREM||5%||1–5 minutes||The person is asleep but their skeletal muscle tone and breathing is the same as when awake.|
|N2 (NREM stage 2): Deeper sleep||NREM||45%||25 minutes in first cycle||The length of this stage increases with each cycle. Bruxism (teeth grinding) may occur.|
|N3 (NREM stage 3): Deepest non-REM sleep||NREM||25%||105 minutes in total, shared between cycles||The deepest stage of sleep, this is when the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system. Sleepwalking, night terrors, and bedwetting may occur. A person is hard to wake. If they are woken at this stage, they may feel groggy for 30–60 minutes after.|
|25%||10 minutes in first cycle, increasing with each cycle.||Associated with dreaming, REM is not restful sleep. Eyes and breathing muscles are active but skeletal muscles are paralyzed. Breathing may be irregular and erratic. Usually follows the other stages, starting around 90 minutes after falling asleep.|
In healthy adults, about
However, as you get older, you’ll need less of this very deep sleep and spend more time in N2.
During the deepest sleep, a variety of
- relaxation of muscles
- increase in blood supply to the muscles
- slowing of heart rate and breathing
- tissue growth and repair
- release of essential hormones
Without deep sleep, these functions cannot take place and you may start to experience the symptoms of sleep deprivation.
How much REM sleep do you need?
There’s no official agreement on how much REM sleep you need, but this stage is important for dreaming, and
For most adults, REM takes up about
How much light sleep do you need?
There is no minimum requirement for light sleep. It is nearly impossible to avoid light sleep if you want to sleep.
How much deep and light sleep do children need?
Babies and children need
- quiet sleep, which is similar to NREM sleep
- active sleep, similar to REM sleep
- indeterminate sleep
They go through only one or two cycles in every period of sleep.
As children grow older, the amount of total sleep they need decreases.
Here are the
|Age||Sleep requirements per 24 hours|
|0–3 months||14–17 hours, with the longest episode lasting |
|4–12 months||12–16 hours, with naps|
|1–2 years||11–14 hours, with naps|
|3–5 years||10–13 hours, with naps|
|6–12 years||9-12 hours|
|13–18 years||8–10 hours|
Signs that children are having sleep problems include:
- learning and memory problems
- frequent illness
However, it is
People may not get enough deep sleep if they:
- don’t sleep long enough
- sleep but toss and turn all night
- work shifts and sleep in the day or have changing sleep patterns
- have jet lag or frequently travel between time zones
- have a health condition that affects their ability to sleep
You can’t force your brain to go into deep sleep, but various strategies may help you get the right amount of quality sleep.
- practicing strategies to manage stress
- establishing sleep routines, such as a bath before bed
- sleeping in a quiet, darkened room with a comfortable temperature
- using an eye mask to block out light
- exercising for
20–30 minutesduring the day but not within the last few hours before bedtime
- avoiding large meals, caffeine, nicotine, and alcohol close to bedtime
- doing relaxation exercises or meditation
- getting up and doing something, such as reading, if you can’t sleep
- leaving distractions, such as phones and other devices, outside the room
A range of sleep trackers may help you track your sleep patterns and see how much light, REM, and deep sleep you are getting.
If you’re aged 18–60 and are sleeping for 7–8 hours per night but are not waking up feeling refreshed, you may not be getting enough deep sleep.
Possible causes of sleep disturbances include:
- obstructive sleep apnea
- pain or other symptoms that can affect sleep
- REM sleep disorder
- a mental health condition, such as depression or anxiety
- older age
- traumatic brain injury
- the use of some medications
Quality sleep is
- the immune system and resistance to disease
- healthy metabolism
- brain, heart, and lung function
A lack of quality sleep may increase the risk of:
- high blood pressure
- type 2 diabetes
- cardiovascular disease
Is 45 minutes of deep sleep enough?
An adult aged 18–60 years needs
However, sleep goes in cycles, so a person may not have 105 minutes of the deepest sleep all in one stage.
What happens if you don’t get the right amount of deep sleep?
In your deepest sleep, your body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system.
If you don’t get enough deep sleep, you may be more prone to physical and mental health issues, as well as feeling sleepy during the day.
How do I increase my amount of deep sleep?
There is no way to make yourself sleep deeper, but you can increase your chances of sleeping well if you follow some tips,
- establishing regular sleep-wake habits, including getting up and going to bed at the same time every day
- ensuring your sleeping space is as quiet, comfortable, and restful as possible
- leaving any devices outside the room while you sleep
- establishing a bedtime routine that helps you relax before sleep, such as having a warm shower or listening to music
Which is better, REM or deep sleep?
All the stages of sleep are necessary, and none is better than any other. You need a balance of around
Getting the right balance of sleep in each stage is essential to health. The five stages of sleep involve light NREM sleep, deep NREM sleep, and REM sleep.
REM sleep is when we tend to dream, and the deepest NREM sleep is when the body relaxes fully and repairs itself.
The amount of sleep we need varies by age, but the CDC recommend
If you’re having trouble with sleep and wakefulness, it’s best to speak with a doctor, as good quality sleep is essential for health and wellbeing.