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We spend a third of our lives asleep—for good reason. Sleep promotes mental health and physical well-being.



Matthew Walker Teaches the Science of Better SleepMatthew Walker Teaches the Science of Better Sleep

Neuroscience professor Matthew Walker teaches you the science of sleep and how to optimize it to better your overall health.

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Why Do We Need Sleep?

Humans need sleep to maintain healthy bodies and minds. Our natural circadian rhythms typically cause us to enter a sleep cycle at least once every 24 hours. Our bodies can release melatonin and adenosine to trigger a sleep cycle, and sleep medicine can also prompt sleepiness. While no two individuals need the same amount of sleep, maintaining a stable sleep pattern provides your body with innumerable health benefits.

Why Is It Important to Get Enough Sleep?

In addition to the benefits listed below, each stage of sleep can help protect the body against hypertension, high blood pressure, heart disease, anxiety, and depression.

  • Sleep helps you process emotions. When you achieve rapid-eye-movement sleep (REM sleep)—the sleep stage in which you experience dreams—the parts of your brain that oversee thinking, memory, and emotions are active. Getting enough sleep each night helps you process that information and improve your mental and emotional health.
  • Sleep promotes memory consolidation and learning. Deep sleep allows you to conserve energy for the next day by lowering your body temperature, blood pressure, and heart rate. This energy conservation promotes increased glucose metabolism, which helps with short- and long-term memory consolidation and learning.
  • Sleep increases cell regeneration. When the pituitary gland releases human growth hormones, your body begins regenerating cells and repairing muscle and tissue. Deep sleep also allows for more cerebrospinal fluid (CSF) to flow into your body, which clears out cell waste. CSF also washes away beta-amyloid—a toxic protein linked to Alzheimer’s disease—from neurons in the brain.
  • Sleep boosts immune system support. The processes that occur during REM sleep and non-REM sleep promote a bolstered immune system. Sleep helps your body fight infection and illness, reduce inflammation, and boost the efficacy of vaccines.

As beneficial as regular sleep can be, its opposite—sleep deprivation—can impair your mental and physical health. A persistent lack of sleep raises the risk of disease and mental decline. Consistent sleep loss (or operating on too little sleep) may not show its effects at first, but prolonged sleep deprivation can be a source of cognitive impairment and poor overall health.

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4 Stages of Sleep

Neuroscientists have determined that the human body goes through four stages of sleep. Three of them are non-REM sleep (NREM sleep), which is sleep without rapid eye movement, the process that causes dreaming. During REM sleep, you have dreams that you may or may not remember.

  1. Stage-1 NREM sleep: This first stage of sleep contains the transition from wakefulness to sleep. Common behavior during this stage includes drowsiness, muscle relaxation, mild twitching, and slow eye movements. Alcohol use can trigger this stage of sleep, but it does not facilitate the more restful forms of deep sleep.
  2. Stage-2 NREM sleep: Better known as light sleep, this sleep stage occurs the most frequently during a full night of sleep. During this stage, your body temperature drops, eye movements stop, and brain waves slow.
  3. Stage-3 NREM sleep: Also known as deep sleep or slow-wave sleep, this is the most regenerative phase of a sleep cycle. Most deep sleep occurs during the first half of the night. During this stage, your brain stem slows your breathing and heart rate.
  4. REM sleep: Characterized by rapid eye movement, this is the dream stage of sleep, and it features intense brain activity. During this sleep stage, your breathing and heartbeat increase, but your muscles undergo paralysis to prevent you from physically acting out the events of your dream. Your heart rate decreases as you cycle back into non-REM sleep


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Want to Learn More About Catching Those Elusive Zs?

Saw some of the best darn logs of your life with a MasterClass Annual Membership and exclusive instructional videos from Dr. Matthew Walker, the author of Why We Sleep and the founder-director of the Center for Human Sleep Science at the University of California, Berkeley. Between Matthew’s tips for optimal snoozing and info on discovering your body’s ideal rhythms, you’ll be sleeping more deeply in no time.