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The Science Of Sleep Cycles & How To Optimize Yours For Better Health

Author:

Jessica Braun Gervais

October 04, 2024

By Jessica Braun Gervais

October 04, 2024

A lack of high-quality sleep can impact your metabolism 1, immune health 2, mood 3, and productivity 4—and there's way more to it than simply clocking seven to nine hours per night.

Your body cycles through four stages as you sleep, and each cycle plays a specific role in helping your body recover.

Learning about the science of sleep cycles and how to regulate them will help you achieve better sleep and improve your overall well-being.

What is a sleep cycle?

There are four phases of sleep, divided into rapid eye movement (REM) and non-REM (NREM). NREM has three stages: N1, N2, and N3.

In a healthy sleep cycle, you complete each of these four stages—and, on average, you'll hit four to six sleep cycles per night.

The sleep cycles are regulated by your body's circadian rhythm, a 24-hour cycle primarily influenced by light and darkness. In an ideal world (without any outside influences), your circadian rhythm will trigger your brain and body to be awake during the day when it's light outside and tired when it's dark.

Stages of a healthy sleep cycle

As mentioned, there are three non-REM sleep stages and one REM sleep stage. Each stage has significance for your body and mind, and many factors can contribute to how well you fall and stay asleep.

Stage 1: N1

N1 is part of the non-REM cycle and is the first stage of light sleep. This stage typically lasts one to five minutes and makes up about 5% of the total sleep cycle.

Alpha waves are one of the primary brain waves associated with the N1 sleep stage. Alpha waves are the brain waves present when you're awake but relaxed. As you enter the N1 stage of sleep, low-amplitude mixed-frequency (LAMF) activity replaces alpha waves 5. As LAMF takes over, it transitions your body and mind from awake to asleep.

During this stage, your breathing remains regular, and your muscles start to relax.

Stage 2: N2

N2 is when your body and mind transition into a deeper sleep, triggering your heartbeat and temperature to drop.

Sleep spindles and K-complexes are present during N2 sleep 5. Sleep spindles are boosts of brain activity that may contribute to memory retention 6. K-complexes are long delta waves that contribute to memory consolidation 7.

In a typical sleep cycle, your first N2 stage lasts about 25 minutes. The stage then becomes slightly longer with each cycle throughout the night.

N2 sleep makes up about 45% of your total sleep cycle.

Stage 3: N3

The N3 sleep stage, often called "deep sleep" (or slow-wave sleep), accounts for about 25% of the sleep cycle.

This stage is when delta waves are present 5, putting the brain and body into a deep relaxation. N3 is also when the body repairs tissues, builds muscle, and strengthens the immune system.

Slow-wave sleep is the most difficult stage to wake up from—and if it is interrupted, you'll likely experience some mental fogginess and disorientation 8.

Stage 4: REM Sleep

The final stage of your sleep cycle is rapid eye movement (REM) sleep, which accounts for about 25% of total sleep time.

Beta waves are present during REM 5, similar to when you're awake. However, unlike when you're awake, skeletal muscles remain dormant while the eyes experience rapid movement—hence the name of the sleep stage.

REM sleep is considered the deepest stage of sleep. This is when your brain is most active and when you're expected to have the most vivid dreams and nightmares 9. REM sleep also contributes to memory consolidation 10, which is how the brain converts short-term memories into long-term memories.

How sleep disorders impact your sleep cycle

A sleep disorder 11 is any condition that disrupts sleep cycles and sleep stages. Common sleep disorders include insomnia, obstructive sleep apnea, circadian rhythm sleep-wake disorders, restless leg syndrome, and parasomnias.

While every sleep disorder affects the body differently, it generally prevents the body and mind from fully relaxing and recovering.

Not getting enough sleep can impact your overall health and wellness, leading to sleep deprivation, mood changes, lower reaction times, trouble learning, and fatigue throughout the day. Risk factors for sleep disorders include certain medications, stress, work schedules, or a family history.

Reasons you're having trouble falling asleep

Many factors contribute to your ability (or inability) to fall asleep. Fortunately, there's a lot you can do to intervene and set yourself up for a night of restorative sleep.

Sleep environment

Your mattress: To achieve quality sleep, you need a bed that's comfortable and supportive. What's best for you depends on factors such as your sleeping position, comfort preferences, budget, and any existing pain or sleep conditions.
Lighting: Too much light in a room could trigger your body to think it's daytime, but for some people, sleeping in a dark room can make it challenging to wake up from a deep sleep. You'll need to find the best balance for you, which could be made easier with sleep masks, sunrise alarm clocks, or blackout curtains (depending on your preference).
Noise: Loud noises can disrupt your sleep cycles. We recommend trying headphones or a sound machine if your sleep is easily interrupted by outside noise.
Temperature: Being too hot or cold is uncomfortable and makes it challenging to relax. Experts recommend keeping your bedroom between 65 and 67 degrees Fahrenheit at night to align with the core body temperature 12 and promote restorative sleep.

Stress

Stress makes it difficult to sleep—and if you don't sleep, it can increase your stress. A lack of quality sleep can elevate your body's cortisol levels (the stress hormone), further increasing stress and disrupting sleep.

Stimulation before bed

Too much stimulation before bed (e.g., watching television, playing video games, or scrolling on your cell phone) can disrupt the circadian rhythm and wreak havoc on your sleep.

Nutrition

Caffeine and alcohol aren't the only culprits when it comes to messing up your sleep. Certain foods can affect serotonin and melatonin 13 activity, and heartburn and GERD 14 may interfere with your sleep by waking you up throughout the night.

Tips for building healthy sleep habits

Even small lifestyle changes can lead to a healthier sleep cycle, which can significantly impact overall well-being.

Give yourself a bedtime

Sleep is a habit—and consistency is key. In fact, a recent study found that sleep regularity was a stronger predictor of certain health conditions and longevity than the total duration of sleep.

Giving yourself a bedtime puts your body and mind into the habit of falling asleep and waking up at the same time every day.

Create a relaxing sleep environment

To achieve deep sleep, your environment should be quiet, dark, and at a comfortable temperature. Many experts also recommend leaving devices like phones and tablets outside the bedroom.

Another tip: Keep the bedroom for sleeping, not for television, work, hobbies, or meals.

Be mindful of naps

While some naps are great for restoration, a recent study found that frequent and late naps may be associated with poor sleep quality and increased awakenings throughout the night.

The takeaway

Understanding how the body gets into the various stages of sleep can help you discover how certain habits, sleep disorders, and other factors contribute to your sleep cycle—and you'll be on your way to achieving optimal health and well-being.