How Sleep Works


Written By: Alison Deshong
Medically Reviewed By: Dr. Sherrie Neustein

According to the CDC, adults need at least seven hours of sleep every night for optimal health. This means spending nearly a third of your life sleeping.

With so much time spent snoozing, it’s natural to wonder why the process of sleep is so critical and how it works. We’ll break down the basics, including the importance of sleep, what happens in your brain when you drift off, how your body knows when it’s time for bed, and ways you can improve your chances of getting a great night’s rest.

Why is Sleep Important?

Scientists and medical experts are still hard at work unraveling the mysteries of sleep. But after decades of research, one thing is clear: it’s hard to overstate the importance of sleep.

Your nightly rest helps regulate a wide range of critical biological functions. Adequate sleep plays a crucial role regulating your mood and metabolism, forming memories and supporting heart health.

What Happens During Sleep?

As an observer, sleep may seem like a passive pursuit. But as you rest, there’s an incredible amount of activity occurring in your brain. Let’s take a closer look at what happens when you sleep.

Stages of Sleep

As you sleep, the electrical activity in your brain shifts from near wakefulness to deep sleep and back again. To distinguish the different types of sleep, researchers categorize sleep into four stages.

Sleep Stage Sleep Category Description Length
Stage 1 NREM Shallow sleep. Stage 1 occurs just after drifting off as your muscles start to relax and your breathing slows. It’s easy to wake up during this first stage of sleep. 1-5 minutes
Stage 2 NREM A stage of light sleep. Your breathing and heart rate continue to slow. You typically spend the most time in stage 2 sleep throughout the night. 10-60 minutes
Stage 3 NREM Deep sleep. Stage 3 sleep is required to feel well-rested. You spend more time in stage 3 earlier in the night. 20-40 minutes
Stage 4 REM Rapid eye movement sleep. This stage is associated with heightened brain activity, quick eye movements under the eyelids, and an increased heart rate. Vivid dreams occur during stage 4 or REM sleep. 10-60 minutes

Note that the stages of sleep fall into two categories:

  • Rapid Eye Movement (REM) Sleep: The type of sleep associated with increased brain activity and dreaming.
  • Non-Rapid Eye Movement (NREM) Sleep: This category represents stages 1 through 3 and accounts for the majority of sleep time.

As you sleep, your brain typically cycles through the four stages of sleep every 90 to 120 minutes. It’s also common to briefly awaken several times throughout the night.

How Does the Body Regulate Sleep?

Your body has an internal clock called the circadian rhythm, also known as the sleep/wake cycle. This daily rhythm ensures that we’re awake and alert during the day and become drowsy and ready for sleep at night.

The circadian rhythm is centered in the brain and works by responding to light cues in our environment. For example, as it gets dark in the evening, cues from your circadian clock promote sleep by releasing melatonin and lowering your core body temperature.

How Much Sleep Do We Need?

You’ve probably heard the standard recommendation of seven to nine hours of sleep. But how much sleep we need varies significantly with age. While seven or more hours is ideal for most adults, infants need a whopping 12 to 16 hours to support their growing brains and bodies.

To help you understand how sleep needs change over time, we’ve compiled sleep recommendations for people of all ages. Keep in mind that the number of sleep hours for young children under 5 includes daily naps.

Age Hours of Sleep Recommended
Newborns 14-17 hours
Infants (4-12 months) 12-16 hours
Toddlers (1-2 years) 11-14 hours
Preschoolers (3-5 years) 10-13 hours
School Aged Children (6-12 years) 9-12 hours
Teenagers (13-18 years) 8-10 hours
Young Adults and Adults (18-60 years) 7-9 hours
Older Adults (over 60 years) 7-8 hours

Tips for Better Sleep

Sleep is often the first activity to hit the chopping block when life gets busy. However, sleep is critical for your well-being, and letting the daily stresses of life encroach on your nightly rest can lead to longer-term issues. Taking just a few moments to make good choices during the day and before bed can set you up for better sleep.

  • Set the Mood: Set the mood for sleep by fine-tuning your bedroom environment. Reduce bright lights and noise that may disrupt your sleep, or consider using a sleep mask and earplugs. Also, make sure your room isn’t too warm, or you may have trouble falling asleep.
  • Get in a Routine: Creating a regular routine can help improve your sleep. Experiment to find which activities work for you. Some ideas include brushing your teeth, taking a warm bath, reading in bed, or performing a short meditation.
  • Cutoff Caffeine Later in the Day: Caffeine offers an excellent productivity boost during the day, but this compound can disrupt your circadian rhythm and delay the natural onset of sleep. Try limiting your caffeine intake to the morning and early afternoon.
  • Nap Mindfully: If you’re having trouble sleeping, consider limiting daily naps to 30 minutes or eliminating napping altogether.


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