Have you been nodding off during those important work meetings or falling asleep at your desk? What about skipping the gym because you can’t muster enough energy to get on the treadmill? If you’re feeling more ho-hum than get-up and go, you might be suffering from a lack of sleep. When you were an infant, sleep was one of the first and most essential activities that you mastered. Although you will spend about one-third of your life doing it, the importance of sleep is often ignored.
Getting enough sleep is even more critical to your health than following a strict diet or daily exercise routine. Quality sleep is the foundation for good health. According to the National Sleep Foundation, catching the right amount of Zzzzs is vital for your body to rebuild tissues, replenish cells and reclaim lost energy. For years, people thought your brain just shut down during sleep but now we know there’s a lot more going on while you snooze.
Why do we need to sleep?
While you’re sleeping, your body is hard at work cleaning up the mess you’ve made during the day. Your systems are busy flushing out toxins, replacing cells, repairing damaged tissues and restoring your energy supply. Sleep gives you the time to heal and recover so you can take on the next day. Not getting enough sleep can lead to a sleep deficit that can have long-term effects on your health, including the risk of diabetes, heart disease, obesity, and depression.
How does sleep work?
As soon as you head to the coffee shop to begin your day, your body is already preparing for sleep. Your sleep and its daily relationship with wakefulness are controlled by two systems, your biological clock or circadian rhythm and your sleep drive. Your circadian rhythm is the biochemical cycle that repeats roughly every 24 hours and governs sleep, wake time, hunger, body temperature, hormone release, and other subtle rhythms that mesh with the 24-hour day. Your sleep drive (the need for sleep) dictates the amount and intensity of sleep you need based on how long you’ve been awake. Think of your sleep drive like hunger; it builds throughout the day until it is satisfied.
What happens when you sleep?
Even though sleep seems like a passive process, it’s not. Sleep is an active state that is as complex as wakefulness. Your brain doesn’t shut down during sleep; rather, your brain is involved in a wide variety of activities.
All of the happenings in your sleep life are built into something that scientists call your “sleep architecture”. That’s a big term for how your sleep is laid out and the process that your body must go through before it feels completely rested. There are two main types of sleep that you need to know about. Non-REM Sleep (NREM), known as the beginning stages of sleep and REM (Rapid Eye Movement) sleep which takes place mostly during the last third of your night’s sleep and is the stage where you may spend some of your time dreaming. While you’re snoozing, you will spend time switching between the two types of NREM and REM sleep. Both are vital to feeling well-rested the next day.
When you’re falling asleep, you are experiencing what’s known as the “waking stage” and then once asleep, your body goes through four stages of sleep. The first three stages occur in NREM sleep and they account for about 75 percent of your sleeping time. The next 25 percent is spent in REM sleep. You’ll then start the cycle over about four times each night and you need between 90 and 110 minutes to complete a sleep cycle.
Here’s what’s happening during those four stages:
Stage 1 is the transitional stage between wakefulness and sleep. In Stage 1 sleep, you shift in and out of consciousness and lose a sense of time and place. Sleep onset—the process of falling asleep—takes place during Stage 1. It is easy to be awakened from this stage of sleep. If awakened from Stage 1 sleep, you might not even be aware you’d been sleeping.
Stage 2 is a phase of light sleep. Over the course of a night and several sleep cycles, you will spend approximately 50 percent of your time in Stage 2 sleep as you move in and out of REM and the deepest stage of NREM sleep. During Stage 2 sleep, brain activity slows down from waking levels. The body also relaxes physically, as heart rate and breathing decrease. Stage 2 is a state of full sleep, but not deep sleep: it is still easy to wake from this stage. During both Stages 1 and 2, the body relaxes as is prepares to move into deeper phases of sleep.
Stage 3 is a phase of deep sleep, also known as slow-wave sleep. Typically it takes about 30 minutes to reach Stage 3 sleep for the first time after falling asleep. During this phase of sleep, brain waves slow considerably. Heart rate and breathing slow, blood pressure lowers, and muscles relax. Stage 3 is a critical time for physical restoration. Repair occurs at the cellular level, restoring strength and function to tissue, muscle, and organs throughout the body. During Stage 3 sleep the body also turns its attention to restoring function to the immune system.
You reach REM sleep for the first time approximately 90 minutes into the night. Periods of REM sleep start as brief, but REM sleep gets progressively longer throughout the night. During REM sleep, the brain increases its activity levels significantly compared the other sleep phases. Most dreaming occurs during REM sleep. If you wake with an awareness of having been dreaming, you likely awoke from REM sleep. REM sleep is a critical phase of sleep for learning and memory, a time when the brain processes and stores information. This is the mental restoration stage of sleep.
How much sleep do you need?
The National Institutes of Health recommends infants sleep 16 to 18 hours each day, preschool-aged children need 11 to 12 hours, and adolescents or school-age children should get around 10 hours of sleep each night. Teens need 9 to 10 hours and adults should expect to get between seven and eight hours each night. But according to The National Sleep Foundation’s Bedroom Poll, 56 percent of Americans were getting less sleep than they needed on work days. That’s more than half with a lack of daily Zzzzs that can lead to a sleep deficit that may have devastating consequences including increased risk for hypertension, diabetes, obesity, heart attack, and stroke. Not clocking enough hours in the bed can also lead to mood disorders, a bad memory and a slew of other health concerns.
National Sleep Foundation, Sleep-Wake Cycle: Its Physiology and Impact on Health.
Division of Sleep Medicine at Harvard Medical School, Sleep and Disease Risk.
National Sleep Foundation, Sleep Drive and Your Body Clock.
National Heart, Lung and Blood Institute, How Much Sleep in Enough?
National Sleep Foundation, 2013 International Bedroom Poll
National Academies Press US (2006), Sleep Disorders and Sleep Deprivation
Center for Disease control and Prevention, 1 in 3 Adults Don’t Get Enough Sleep.