How Sleep Cycles Affect Your Mind and Body

Sleep is important for your physical and mental health. Learn about the sleep cycles your body goes through at night and how they can impact your health.
*Note - this is a guest post shared on behalf of the National Council on Aging.
Originally posted here --

Key Takeaways

  • High-quality sleep is essential to good physical and mental health.
  • A sleep cycle consists of four sleep stages, which your body needs to restore and maintain your health.
  • Although sleep needs may vary, adults between the ages of 18 to 64 need approximately 7 to 9 hours of sleep, and those age 65 and older need 7 to 8 hours nightly.

Getting quality sleep can be challenging. And as we age, older adults often experience less total time sleeping, along with more disruptions to their sleep. Additionally, many sleep issues become more common for older adults, such as insomnia, sleep apnea, restless leg syndrome, sleep disorders, and stress.

How much sleep do you need each night? Adults between the ages of 18 to 64 need approximately 7 to 9 hours of sleep, while adults age 64 and older need about 7 to 8 hours per night. [1] Lack of adequate sleep affects mood, thinking, and ability to learn and function. A good night’s sleep depends on the sleep cycle, which is made up of four sleep stages. Understanding the sleep cycle stages may be one way to help you catch more Zzzzs.

What is a sleep cycle?

A sleep cycle is the period of time when your brain and body rotate through the four sleep stages. Typically, a full night of rest will allow for four to six sleep cycles. To achieve highly restorative sleep, you need to progress easily through the four stages of sleep, as each plays an important role in maintaining your physical and cognitive health. The average sleep cycle lasts 80 to 100 minutes, at which point it starts over. [2]

The four stages of sleep

An infographic showing the four stages of sleep: light sleep, deeper sleep, deepest sleep, and rapid eye movement.

Each sleep cycle is made of four sleep stages and typically lasts 80 to 100 minutes.

The four stages of sleep fall into one of two phases, non-rapid eye movement (NREM) sleep and rapid eye movement (REM). NREM sleep accounts for 75 to 80% of the sleep cycle, and is characterized by slowed brain waves, heart rate, and muscle activity. [3]

The first stage of sleep, stage 1, lasts only one to seven minutes, beginning when you first relax to the point of drifting off to sleep. By stage 2, your body adapts by slowing down your breathing and heart rate, and your body temperature drops. In stage 3, your body, breathing, and mind are the most still, and you get the deepest sleep. These first three stages of NREM sleep take approximately 90 minutes to complete.

Stage 4 is the REM sleep stage, where your body is still while your mind is active. The REM stage is the dream stage and one that occurs before the cycle starts over. It can last anywhere from 10 minutes up to an hour before transitioning back to stage 1. [4]

Table 1 Comparison table of the 4 stages of sleep

Sleep stages vary, but generally, this is what most people experience during their nighttime slumber.

Sleep stage

Type of sleep


Main function

Stage 1

Light sleep. Your brain, heart rate, and breathing slow.

1–7 minutes

You get into a calm, relaxed state.

Stage 2

Deeper sleep. Body temperature drops, and your vital signs slow down.

10–25 minutes

Your brain is organizing memories.

Stage 3

Deepest sleep. You become very still.

20–40 minutes

Your body and mind are healing and recovering from physical and mental stress.

Stage 4

REM sleep. Your brain becomes active, your eyes dart back and forth.

10–60 minutes

You are in an active state when you dream.

The importance of sleep

Sleep is essential to good physical and mental health as it affects many of our internal systems, like the heart and circulatory system, hormone balance, metabolism, respiratory, and immune systems. Additionally, sleep affects our cognitive function and impacts learning, information recall, and forming long-term memories. [5]

Sleep and the body’s defense system, the immune system, affect each other in a feedback loop. Sleep disturbances can affect blood pressure, worsen inflammation, and cause an imbalance in the hormones that regulate hunger. Additionally, people who do not sleep enough are at risk for colds and other infections.

People with asthma and other lung conditions can have difficulties getting a good night’s sleep due to breathing less and taking in less oxygen. Supplemental oxygen can improve sleep quality in some cases.

A study published in the journal Science found that sleep allows the brain to sort and reinforce new memories in a process called consolidation, leading to long-lasting memories and better information recall. [5] As sleep enables the brain to sort through daily memories and activate neural networks, it serves an important role in the brain’s ability to learn and store new knowledge. Similarly, sleep deprivation can negatively impact memory and the ability to focus, make decisions, and control emotions or behavior.

Understanding the cycles of sleep may help you figure out why your sleep may not be optimal and provides a way to help you improve your sleep hygiene .

What affects sleep stages?

Sleep patterns change through the course of our lives. Even though we need just as much sleep as before, getting a full night’s sleep can be challenging for those who have physical, psychological, or lifestyle changes. As we age, we tend to wake up more during the night, and our deep sleep tends to decrease. The circadian rhythm , the body’s internal sleep-wake cycle, can change as well. This internal clock controls the release of naturally occurring hormones cortisol and melatonin and also manages core body temperature. [6]

Chester Wu, MD, a psychiatrist and sleep specialist in Houston, Texas, said sleep issues develop for several reasons as we age. “Your circadian rhythm shifts earlier, so you may find yourself waking up earlier and your circadian rhythm ‘flattens,’ so sleep-wake signals become weaker, causing more awakenings,” he said.

He also noted pain, trouble getting comfortable, snoring, and sleep apnea interfere with sleep.

People with sleep issues like obstructive sleep apnea (OSA) may experience daytime sleepiness as a result. OSA causes low blood oxygen levels, called hypoxemia, and sleep disturbances. Approximately 34% of men and 17% of women in mid-age have this condition, according to the American Heart Association. [7] Using a CPAP machine, which pumps mild air pressure to keep airways open, can help a person get a better night’s sleep. [8]

Many health care professionals clock long hours and work overnight, which disturbs their circadian rhythm. This disturbance causes poorer sleep quality, leading them to experience trouble falling and staying asleep. [9]

Jet lag is another sleep cycle disruptor. People taking a trip across the country or globe can face challenges resetting their circadian rhythm upon arrival.

Inefficient sleep can lead to or worsen mental health issues, including depression. A study published in the Journal of Affective Disorders connects the dots between sleep and depression, drawing a connection between people who get fewer than 8 hours of sleep per night and a higher rate of depression than people who get 8 or more hours. [10] The good news is exercise can both ease depression and improve sleep at the same time. [11] Aerobic exercise (walking and swimming), weight training, and mind-body exercises such as breathwork and guided imagery are all good options for moving your body and calming your mind.

Other studies have made the connection between insufficient sleep and cardiovascular conditions such as coronary heart disease and heart attacks. [12] [13] One study showed people who get fewer than 6 hours of sleep had a 20% higher risk of heart attack, and those who slept longer than 9 hours regularly had a 34% higher risk for heart attack.

How can I get better sleep?

Understanding the importance of sleep serves as a great first step in improving your sleep quality. Throughout your day, there are practices you can use to promote better sleep at night. Here are some tips to improve your sleep hygiene: [14]

  • Turn off electronics: Turn off your phone when you are getting ready for bed. Phones emit blue light that can stimulate your brain the way sunlight does.
  • Invest in a new bed: Adjustable beds can help improve your comfort, and help you get restful sleep.
  • Keep naps short: Naps are a great way to recharge, but should only last around 30 minutes. Sleeping too long during the day can affect your nighttime sleep.
  • Cut caffeine: Drink your last cup of coffee before noon.
  • Reduce alcohol consumption: Although alcohol has a sedative effect and may make you feel sleepy, it actually inhibits your ability to stay asleep during the night.
  • Get sunlight: Getting natural light during the day can help keep your circadian rhythm on track.
  • Exercise: Staying active has many physical and emotional benefits. Getting in exercise sessions during the day can help you sleep at night.
  • Manage your stress: Consider keeping a journal or seeking therapy if sleep eludes you due to stress.
  • Set a sleep schedule: You’ll get better sleep if you can keep to a schedule and consistent wake time.

“As easy as it may be to justify staying out a few hours later than usual, you should aim to go to bed at the same time every night. In the morning, try to wake up at the same time, even on weekends,” said Chad Denman, MD, a sleep medicine specialist in Austin, Texas.

“While sleeping in might feel nice from time to time, it can be disruptive to your natural sleep cycle,” Denman added.

Bottom line

Getting a good night’s sleep is essential for our physical and mental health. Understanding the stages of your sleep cycles can help you manage your quality of sleep. A sleep cycle is the period of time your brain and body go through during four sleep stages. The circadian rhythm, the body’s internal sleep-wake cycle, may not be as effective as you age. A lack of sleep can have adverse effects on mood and body, and make existing conditions worse. Luckily, there are good habits you can practice to promote healthy sleep.

Frequently asked questions

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  2. National Institutes of Health. Sleep Phases and Stages. Found on the internet at
  3. What Happens During Sleep? National Institute of Child Health and Human Development. April 29, 2019. Found on the internet at
  4. How sleep works. March 24, 2022. National Institutes of Health. Found on the internet at
  5. Girardeau G, Lopes-Dos-Santos V. Brain neural patterns and the memory function of sleep. Science. 2021. Found on the internet at
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  7. Boivin DB, Boudreau P, Kosmadopoulos A. Disturbance of the Circadian System in Shift Work and Its Health Impact. Journal of Biological Rhythms. February 2022. Found on the internet at
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  12. Zhuang Z, et al. Association of physical activity, sedentary behaviours and sleep duration with cardiovascular diseases and lipid profiles: a Mendelian randomization analysis. Lipids in Health and Disease. May 8, 2020. Found on the internet at
  13. Daghlas I, et al. Sleep Duration and Myocardial Infarction. Journals of the American College of Cardiology. Sept. 10, 2019. Found on the internet at
  14. Centers for Disease Control and Prevention. Tips for Better Sleep. Found on the internet at