Sleep is a vital component of health, and according to the CDC, roughly 1 out of 3 adults do not get enough sleep. We think of sleep as one continuous state and time, but it actually consists of different stages which cycle multiple times throughout a night. On average, a full sleep cycle goes on for about 90 to 110 minutes, with the average adult performing 4 to 6 full sleep cycles. Each stage is crucial for physical restoration, cognitive function, and emotional stability. Seemingly while we are resting, our bodies are constantly performing important functions during these stages, from brain function, to repairing muscles, and everything in between.
What is a Sleep Cycle?
Sleep cycles are the physiological processes through which we experience the stages of sleep throughout a typical night of sleep. While we are asleep, we do not remain in a single state of sleep all night; however, we cycle through distinct periods of light, deep, and REM sleep in the following way. Each cycle lasts on average about 90 to 110 minutes, and everyone typically goes through 4 to 6 cycles per night depending on how long they sleep.
A sleep cycle can be split into two larger parts:
- Non-Rapid Eye Movement (NREM) Sleep
- Rapid Eye Movement (REM) Sleep
These two parts are then further broken down into smaller stages serving a different purpose, in terms of rest, recovery, and brain processing.
Breakdown of a Typical Sleep Cycle
| Sleep Stage | Type | Duration (in min) | % of Total Sleep | Key Characteristics |
|---|---|---|---|---|
| Stage 1 | NREM | 1–7 | ~5% | Lightest sleep; transition from wakefulness; easily awakened |
| Stage 2 | NREM | 10–25 | 45–55% | Body temperature drops; heart rate slows; preparation for deep sleep |
| Stage 3 (Deep Sleep) | NREM (Slow Wave) | 20–40 | 13–23% | Most restorative stage; essential for physical repair and immune function |
| REM Sleep | REM | Starts ~90 | 20–25% | Vivid dreams; brain activity increases; vital for memory, learning, and emotional health |
Stage 1 (NREM): This is the lightest stage of sleep and is often characterized as a transition between sleep and awake. Stage 1 can last anywhere from 1 to 7 minutes and makes up approximately 5% of total sleep.
Stage 2 (NREM): Heart rate and body temperature are beginning to drop, and the body is becoming prepared for deep sleep. Stage 2 makes up about 45-55% of total sleep.
Stage 3 (NREM Deep Sleep): Sometimes referred to as slow-wave sleep, deep sleep is the most restorative stage of sleep. Stage 3 sleep is essential for physical healing, immune function, and growth. Deep sleep generally makes up 13-23% of the sleep cycle in healthy adult populations.
What is REM Sleep?
Rapid Eye Movement (REM) sleep is the most important stage of sleep that takes place about 90 minutes after falling asleep. REM sleep is characterized by rapid movements of the eyes under a closed eyelid, increased brain activity, and vivid dreaming. In a healthy sleep pattern, the brain is about as active during REM sleep as when awake, but while the muscle system is relaxing to nearly the point of paralysis (muscle atonia) so that not even a dream will cause the subject to move!
The heart rate and respirations are more irregular, and thermoregulation (the body's ability to regulate its own temperature) is precluded. The later periods of REM sleep are lengthened, with the final event lasting almost an hour, and this sleep state usually accounts for 20–25% of an adult's total sleep time. REM is not only important to the cognitive function of memory and problem-solving but also emotional function and regulation.
When REM is inhibited by stress, alcohol, or a sleep disorder, the person becomes crumbly because of these emotional repercussions—think of becoming cranky! When once stable moods manifest as mood disturbances, concentration is affected, memory becomes sporadic, and again we become cranky!
Key Features of REM Sleep
- Rapid Eye Movements: The stage gets its name from the quick, darting movements of the eyes beneath closed eyelids.
- Increased Brain Activity: Brainwaves during REM resemble those of wakefulness, making this stage essential for mental and emotional health.
- Dreaming: Most vivid and memorable dreams occur during REM sleep.
- Muscle Atonia: While the brain is highly active, voluntary muscles become temporarily paralyzed to prevent you from acting out dreams.
- Heart Rate and Breathing: These become irregular and can increase during REM sleep.
How Does Sleep Cycle Impact Your Sleep?
Sleep cycles are critical in determining the quality and depth of your sleep, as well as the restorative benefits associated with it. Each night, your body proceeds through a number of sleep cycles of approximately 90 to 110 minutes each, and each cycle contains NREM (Non-Rapid Eye Movement) sleep and REM (Rapid Eye Movement) sleep.
The following outlines factors that sleep cycles affect:
Quality of Sleep: Completing a full cycle through all the sleep stages ensures that your sleep will be restorative and restful.
Recovery from Physical Effort: Deep stages of NREM sleep provide benefits such as muscle repair, cell regeneration and enhanced immune systems.
Memory and Learning: REM sleep supports memory consolidation and aids in learning and problem-solving.
Mood and Emotional Health: Appropriate REM sleep regulates emotions and decreases the likelihood of anxiety or depression.
Grogginess: The initial effects of grogginess and confusion (a phenomenon known as sleep inertia) are greater if you wake up within the context of a cycle of sleep, particularly deep sleep.
Cognitive Performance: Going through complete sleep cycles will enhance daytime alertness, focus and decision-making/reasoning abilities.
Hormonal Regulation: Sleep cycles influence the secretion of hormones such as melatonin, cortisol and growth hormone.
Impacted by Sleep Length or Timing: When sleep is limited due to short duration or irregular patterns, the sleep cycles are truncated, limiting your recovery and performance.
Tips to Maintain a Heathy Sleep Cycle
Here are some effective tips to maintain a healthy sleep cycle:
1. Keep a Regular Sleep Schedule
Going to bed and waking up at the same time every day, including weekends, regulates your circadian rhythm. When you stick to a schedule, your body learns to feel sleepy when it is sleepy and will wake up feeling more refreshed. Follow these tips to maintain a healthy sleep schedule.
2. Limit Your Screen Time Before Bed
When you use smartphones, laptops, or TVs, you expose your eyes to blue light. Blue light can suppress melatonin production, which means blue light makes it harder to get to sleep. It is recommended to avoid screen time for at least 60 minutes before bed, so your brain is less stimulated and your transition into sleep will be smoother.
3. Establish a Relaxing Bedtime Routine
Having a calming set of activities signalled to your brain to get some sleep. Reading, stretching, journaling, and even a warm bath are low-stress activities that will help to reduce your stress level and calm you mentally.
4. Avoid Caffeine and Nicotine Late in the Day
Caffeine can stay in your system for a long time, typically 6–8 hours, meaning caffeine can affect your ability to fall asleep. Nicotine is a stimulant, which means to increases or maintains alertness. Be mindful of your caffeine and nicotine in late afternoon or evening to help you protect your sleep quality.
5. Avoid Heavy Meals and Alcohol Before Bedtime
You may develop indigestion if you eat a large meal or spicy foods before bedtime, which will disrupt your ability to both get to sleep and stay asleep. Similarly, alcohol sedates people, which is how it helps them get to sleep, but, quickly wears off and disrupts REM sleep.
6. Get Natural Light Exposure
Natural light exposure during the day helps your circadian clock stay synchronized. Aim to spend a minimum of 20–30 minutes of outside time each day, ideally during the morning.
7. Stay Active During the Day
Physical activity fosters deeper and restorative sleep. Ensure you're getting at least 30 minutes of moderate activity on most days, while avoiding vigorous activity right before going to bed.
8. Keep The Sleep Surroundings Comfortable
Darkness, cool air, and quiet space make sleep much easier. Consider blackout curtains, earplugs or white noise machines and a bedroom temperature of about 60–67°F (16–19°C) for comfort.
9. Limit Naps or Keep Them Short
Naps, as long as they are short (20–30 minutes), are refreshing, whereas longer naps or naps in the afternoon may disrupt your overnight sleep cycle. If you must nap, consider doing it earlier in the day.
10. Go to bed only when you are tired
When you are lying in bed awake, it is all too easy to get frustrated and anxious. If you can't sleep after about 20–30 minutes, get up and do a calming activity until you feel sleepy.
Final Thoughts
Your sleep cycle has an important role in your ability to rest and restore each night. Each stage - light sleep, deep sleep, and REM - is important for different aspects of your physical, mental, and emotional well-being. If your sleep cycle is disturbed, it can lead to poor sleep quality, tiredness, and mood disturbances. Maintaining healthy habits like a consistent sleep schedule and a calming bedtime routine will help you promote complete and balanced sleep cycles, resulting in improved physical, mental, and emotional well-being.
