Sleep Cycles: How Many Do You Really Need?

Sleep is a complex and mysterious body process, and getting enough of it is critical to your health. The amount of sleep you get can affect everything from weight and metabolism to brain function and mood. Sleep cycles are composed of four stages: three non-rapid eye movement (NREM) stages and one rapid eye movement (REM) stage. A person will typically go through four to six sleep cycles per night, with each cycle lasting around 90 minutes. The first sleep cycle is often the shortest, ranging from 70 to 100 minutes, while later cycles tend to be longer.

Each sleep stage serves a different purpose and plays a part in allowing the mind and body to wake up refreshed. Stage 1 is when a person first falls asleep, which normally lasts just one to seven minutes. During this stage, the body has not fully relaxed, though body and brain activities start to slow with periods of brief movements. In stage 2, the body enters a more subdued state, including a drop in temperature, relaxed muscles, and slowed breathing and heart rate. Stage 3 is deep sleep, and it is harder to wake someone up during this phase. The brain activity during this period has a distinct pattern of delta waves. Finally, during the REM stage, brain activity picks up and the eyes move quickly from side to side, though the body experiences temporary paralysis.

The amount of sleep needed varies depending on age, health, and lifestyle. For example, newborns need the most sleep, around 14–17 hours every 24 hours, while adults are recommended to get seven to nine hours of sleep per night.

How much sleep do you need?

Sleep is a complex and mysterious process, and it's something many people struggle with. While it might seem simple, it's actually one of the most complex body processes known to science.

The amount of sleep a person needs varies from person to person and can change throughout their lifetime. The number of hours of sleep that are good for a person's health can also change as they age.

In general, the recommended amount of sleep by age is:

• Newborns (birth to 3 months): 14 to 17 hours
• Infants (4 to 11 months): 12 to 16 hours (including naptime)
• Young children (1 to 5 years): 10 to 14 hours (including naptime)
• School-aged children (6 to 12 years): 9 to 12 hours
• Teenagers (13 to 18 years): 8 to 10 hours
• Adults (18 to 64 years): 7 to 9 hours
• Seniors (65 years and older): 7 to 8 hours

However, these sleep amounts are not universal. Some people need more sleep, and others less. Variations in sleep requirements may even be genetic. For example, some people can inherit the "short sleeper" trait from a parent.

Personal circumstances and health status can also affect how much sleep a person needs. People who are sick, recovering from an injury or medical procedure, or pregnant may need more sleep.

If you're unsure how much sleep you need, it's a good idea to talk to a healthcare provider. They can help you understand if there might be an underlying medical issue that needs addressing.

Sleep Cycles

While the number of hours of sleep is important, it's also crucial to consider sleep quality and whether the time spent sleeping is restorative. A good night's sleep involves progressing smoothly through multiple sleep cycles, each composed of four separate sleep stages.

Each sleep stage plays a part in allowing the mind and body to wake up refreshed. Understanding the sleep cycle also helps explain how certain sleep disorders, such as insomnia and obstructive sleep apnea, can impact a person's sleep and overall health.

On average, a person goes through four to six sleep cycles per night, with each cycle lasting around 90 to 120 minutes. The first sleep cycle is often the shortest, ranging from 70 to 100 minutes, while later cycles tend to be longer, falling between 90 and 120 minutes.

The four stages of the sleep cycle are:

• Stage 1 (N1): Light sleep where the body first transitions from being awake to falling asleep. This stage lasts about 1 to 7 minutes, with the body and brain activities starting to slow down, and the heart rate, breathing, eye movements, and brain waves all decreasing.
• Stage 2 (N2): A deeper sleep where the body temperature drops, muscles relax, and breathing and heart rate slow further. This stage lasts about 10 to 25 minutes during the first cycle and increases with each subsequent cycle.
• Stage 3 (N3): Deepest sleep stage where the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system. This is the most challenging stage to wake someone from, and if awakened, they may experience "sleep inertia," feeling groggy for 30 to 60 minutes afterward.
• REM sleep: The final stage of the cycle, characterised by rapid eye movements. The eyes move quickly behind closed eyelids, and the body experiences atonia, a temporary paralysis of the muscles except for the eyes and breathing muscles. This stage is associated with dreaming and more vivid dreams due to increased brain activity.

The first REM stage is usually short, lasting only a few minutes, but it gets longer with each subsequent cycle, especially in the second half of the night. While the sleep cycle starts with N1, the progression then follows the order: N2, N3, N2, REM.

Optimising Sleep

To optimise your sleep cycles and ensure you're getting enough restorative sleep, it's important to practice good sleep hygiene. This includes:

• Maintaining a consistent sleep and wake schedule, even on weekends and vacations.
• Having a bedtime routine to signal to your brain that sleep is approaching.
• Avoiding bright lights and electronics, especially before bedtime, as they can disrupt your body's natural sleep-wake functions.
• Avoiding heavy meals, caffeine, nicotine, and alcohol close to bedtime, as they can disrupt sleep.
• Engaging in physical activity during the day to improve sleep quality.
• Using your bedroom primarily for sleeping and intimacy to create a strong sleep-related association with the space.
• Maintaining a healthy weight, as excess weight can increase the risk of developing sleep apnea.

Additionally, creating an ideal sleep environment is crucial. Keep your bedroom cool, dark, and quiet, and consider using an eye mask or earplugs if needed.

Sleep Deprivation

Chronic sleep deprivation can have adverse effects on your health and well-being. Not getting enough quality sleep can impact your body and brain's ability to function properly, leading to:

• Trouble thinking or concentrating.
• Mood changes, including irritability, depression, or anxiety.
• A weakened immune system, making you more susceptible to illness.
• Metabolism problems and an increased risk of developing Type 2 diabetes.
• Fatigue and exhaustion.

Long-term sleep deprivation can also contribute to more severe health issues, including:

• Cardiovascular disease.
• Metabolic conditions like Type 2 diabetes.
• Cognitive impairment.
• Mood disorders.
• Obesity.
• Stroke.
• Dementia.

What is the sleep cycle?

The sleep cycle is a physiological process that occurs during sleep, allowing the brain and body to perform "housekeeping" functions, such as repairing or growing tissues, removing toxins, and processing memories. Each sleep cycle consists of four stages, with each having varying effects on the body.

The four stages of the sleep cycle are:

• Stage one: This is a period of light non-REM sleep, during which a person's heart rate, breathing, eye movements, and brain waves slow down. The muscles also relax, although they may twitch occasionally. This stage is short, lasting around 5-10 minutes.
• Stage two: This is a period of deeper non-REM sleep, where the muscles relax further, eye movements stop, and body temperature drops. During the first sleep cycle of the night, this stage lasts for around 25 minutes, lengthening with each new sleep cycle. Overall, it accounts for more than 50% of sleep in adults.
• Stage three: This is the deepest stage of non-REM sleep and the hardest to awaken from. During this stage, heart rate, breathing, and brain waves become regular. A person will experience the most deep sleep during the first half of the night, and with each sleep cycle, the amount of deep sleep decreases. This is the stage people typically find most difficult to wake from, and if they do wake during this stage, they may feel mentally foggy for around 30-60 minutes. The overall percentage of deep sleep tends to decrease with age.
• REM sleep: The term "REM" refers to a person's rapid eye movements during this stage. Their breathing also quickens and becomes more erratic, while other vital signs, such as blood pressure and heart rate, become less regular. REM sleep is the stage most associated with dreaming, although dreaming can also occur in other stages. During REM sleep, most people experience muscle atonia, or temporary muscle paralysis, which is natural and prevents them from acting out their dreams. During the first sleep cycle, REM sleep lasts for approximately 10 minutes, increasing in length as the night progresses. In the final cycle of sleep, REM can last up to an hour.

On average, adults go through four to six sleep cycles per night, and each cycle lasts around 90 minutes. However, not all sleep cycles are the same length, and they can vary from person to person and from night to night based on factors such as age, recent sleep patterns, and alcohol consumption.

What are the stages of sleep?

A typical night's sleep consists of four to six sleep cycles, each composed of four distinct stages. These stages are determined by analysing brain activity during sleep, which shows distinct patterns that characterise each stage. The stages are as follows:

Stage 1 (N1)

Also known as N1, this is the lightest stage of sleep and occurs right after you fall asleep. The body has not fully relaxed, and there are still brief periods of movement. Brain activity slows down, and it is easy to wake someone during this stage. Stage 1 normally lasts just one to seven minutes, and an uninterrupted sleeper may not spend much time in N1 as they move through further sleep cycles.

Stage 2 (N2)

During this stage, the body enters a more subdued state. Muscle tension eases, and breathing and heart rate slow down. Brain waves show a new pattern, and eye movement stops. Brain activity slows, but there are short bursts of activity that help resist being woken up by external stimuli. Stage 2 can last for 10 to 25 minutes during the first sleep cycle, and each subsequent N2 stage can become longer. Collectively, a person typically spends about half their sleep time in N2.

Stage 3 (N3)

Also known as delta sleep or slow-wave sleep, this is the deep sleep stage. It is harder to wake someone up during this phase. Muscle tone, pulse, and breathing rate decrease further as the body relaxes. Brain activity during this stage is characterised by delta waves. Experts believe this stage is critical for restorative sleep, allowing for bodily recovery, growth, and a boost to the immune system. Memory, creativity, and insightful thinking are also thought to be aided by this stage. You spend the most time in deep sleep during the first half of the night, with N3 stages lasting for 20 to 40 minutes in the early sleep cycles. As the night goes on, these stages get shorter, and more time is spent in REM sleep.

Stage 4 (REM)

REM sleep is characterised by rapid eye movement and increased brain activity. The eyes move quickly behind closed eyelids, and the brain activity is similar to that of a waking person. The body experiences atonia, a temporary paralysis of the muscles except for the eyes and the muscles that control breathing. REM sleep is associated with dreaming and is believed to be essential for cognitive functions like memory, learning, and creativity. The first REM stage is usually short, lasting only a few minutes, but later stages can last for around an hour. In total, REM stages make up around 25% of sleep in adults.

How much deep sleep is ideal?

Deep sleep is essential for health and well-being. Most adults need around 1.5–2 hours of deep sleep per night. The Centers for Disease Control and Prevention (CDC) advise adults aged 18–60 years to aim for at least 7 hours of sleep per night, with around 25% of this being deep sleep.

Deep sleep is the third of four stages in a sleep cycle. The first stage is a transition to sleep, the second is light sleep, the third is deep sleep, and the fourth is REM (rapid-eye movement) sleep. A person will typically go through four to six sleep cycles per night, with each cycle lasting around 90–120 minutes.

During the deepest sleep stage, a variety of functions take place, including:

• Relaxation of muscles
• Increased 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.

In healthy adults, about 70% of sleep is deep sleep, and around 25% is the deepest sleep. So, if you sleep for 7–8 hours, you should spend around 105–120 minutes in your deepest sleep. However, as you get older, you will need less of this very deep sleep and will spend more time in the second stage of sleep.

If you are 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. You might want to ask a doctor about doing a sleep study to help figure out your sleep patterns. You may need treatment for a sleep disorder.

How to Get More Deep Sleep

You cannot force your brain to go into deep sleep, but various strategies may help you get a better night's rest:

• Practicing stress management techniques
• Establishing a bedtime routine, such as taking a bath before bed
• Sleeping in a quiet, dark, and comfortable bedroom
• Using an eye mask to block out light
• Taking a 20–30 minute nap during 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 else, such as reading, if you cannot sleep
• Leaving phones and other devices outside the bedroom

How can I get more deep sleep?

On average, a person will go through four to six sleep cycles per night, with each cycle lasting around 90 to 120 minutes. The first sleep cycle is often the shortest, ranging from 70 to 100 minutes, while later cycles tend to be longer. Each cycle consists of four stages: three stages of non-rapid eye movement (NREM) sleep and one stage of rapid eye movement (REM) sleep.

Stage N3, or deep sleep, is the deepest stage of sleep and the hardest to awaken from. During this stage, the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system. Most adults need around 1.5 to 2 hours of deep sleep per night, and it usually occurs during the first half of the night.

• Manage your stress: Stress and anxiety can cause sleep fragmentation, making it easier for you to wake up. Try practising relaxation techniques such as deep breathing, meditation, or yoga.
• Establish a sleep routine: Stick to a consistent sleep schedule, even on weekends. Go to bed and wake up at the same time every day. This helps regulate your body's internal clock and improves your body's ability to wake up naturally.
• Create a bedtime routine: Develop a pre-sleep ritual such as reading a book, listening to soothing music, or taking a warm bath to signal to your body that it's time to wind down and prepare for sleep.
• Optimise your sleep environment: Make sure your bedroom is quiet, dark, and maintained at a comfortable temperature. Use earplugs or an eye mask if necessary to block out any noise or light.
• Limit distractions: Leave your phone and other electronic devices outside the room while you sleep. The blue light emitted by these devices can disrupt your sleep, and the notifications can be distracting.
• Avoid stimulants: Refrain from consuming caffeine, nicotine, or alcohol close to bedtime, as these substances can disrupt your sleep. Instead, opt for a light snack if you feel hungry before bed.
• Exercise during the day: Engage in regular physical activity during the day, but avoid exercising too close to bedtime, as it may energise you and make it difficult to fall asleep.
• Nap wisely: Napping can be beneficial, but be mindful of the duration and timing. Limit your naps to 20–30 minutes during the day, and avoid napping too close to bedtime to prevent disrupting your nighttime sleep.
• Seek medical advice if needed: If you continue to experience difficulties with sleep, consider consulting a healthcare professional. They can help assess your symptoms and determine if any underlying conditions or sleep disorders are affecting your sleep quality.

Frequently asked questions