Understanding sleep cycles and the stages of sleep
March 17, 2023
At the end of the day, after you’ve crawled into bed and are all done reading or scrolling and you finally turn out the lights and close your eyes, you may think you and your brain are about to shut down for the next several hours.
That’s what sleep is, right? A dormant stage so your body can rest up for another day. In a way, yes. But when you’re sleeping, your brain and body are far from dormant. While you’re checked out, the rest of you is actually going through multiple stages of sleep ranging from light sleep to deep sleep to dream-filled sleep, all with different levels of brain activity, heart rates and blood pressure.
Ready to be a sleep geek? Here’s what you need to know to about sleep cycles, sleep stages, deep sleep and REM sleep. Try to stay awake!
There are four stages of sleep that collectively make up the sleep cycle. Your body cycles through all four sleep stages multiple times a night. Within those stages, there are two types of sleep: rapid eye movement sleep, or REM sleep, and non-REM sleep. The first three sleep stages are non-REM sleep while the fourth is REM sleep. Here’s what a typical sleep cycle looks like:
Sleep stage 1: This is when you’re drifting off into a light sleep. It can last for several minutes. During sleep stage 1, your heartbeat, breathing, eye movements and brain waves slow down and your muscles relax.
Sleep stage 2: You’re still sleeping lightly, but your body is getting ready for deep sleep. Everything slows down even further, your eyes stop moving and your body temperature lowers. Your brain waves are generally slow, but they are punctuated by spikes of electrical activity. This sleep stage can last for about 25 minutes.
Sleep stage 3: Deep sleep. This is the restorative stage of the cycle. This is when all activity—breathing, heartbeat, brainwaves, muscles—are at their lowest levels. At the cellular level, however, your body is getting to work growing, developing and repairing muscle and tissue. It’s also when your immune system is recharging. These sleep stages can last from 20-40 minutes per cycle, with the longer spans happening earlier in the night.
Sleep stage 4 – REM sleep: You enter REM sleep the first time about an hour and a half after you first fall asleep. REM sleep is named for the rapid eye movements that happen during this sleep stage. REM sleep can last for a few minutes early in the night lengthening up to an hour as the morning nears.
During REM sleep, your brain activity, heart rate and blood pressure are close to the same levels as when you’re awake, while your muscles undergo temporary paralysis—except for those responsible for your eyes and breathing. This helps prevent you from acting out all those crazy things you’re dreaming about. (Whew!)
Sleep cycles vary in length. They change throughout the night and also as people age. The typical length of the first sleep cycle of the night is 70-100 minutes with the later cycles lengthening to 90-120 minutes.
In general, stage 1 can last for 1-7 minutes. Stage 2 can last for 10-25 minutes. Stage 3 for 20-40 minutes and stage 4 for 10-60 minutes.
As we said above, deep sleep is the restorative stage. It’s the good stuff that can make you wake up feeling refreshed and ready to take on whatever life throws at you. This sleep stage is also called slow-wave sleep, a description of the brain wave activity during this time.
It’s the most difficult to wake someone up during this sleep stage, especially children. If you’re prone to sleep walking or night terrors, this is the stage in which they happen.
Children get quite a bit more deep sleep than adults do. Deep sleep in children decreases steadily (by about 7% every 5 years) between the ages of 5 and 15. In adults, deep sleep continues to decrease each decade, only by smaller amounts. Deep sleep may comprise about 13-28 percent of the total sleep for a young adult, while it may disappear from people’s sleep cycles altogether by the time they’re in their 60s.
REM sleep is your literal dream world, but it’s also when your brain is busy. Research suggests that this stage supports cognitive health and emotions. This is when your brain sorts through memories, retaining and consolidating the important ones for the long term and deprioritizing the minor ones.
Infants and children need considerably more REM sleep than adults because their brains are still developing. A healthy sleep cycle for adults dedicates about 20%-25% of total sleep time to REM sleep. If your normal night is the recommended 7-8 hours of sleep, that’s around 90 minutes of total REM sleep, give or take.
If you’re interested in learning more about your own sleep cycle, there is an ever-growing list of sleep trackers on the market to help you.
Most fitness trackers and smart watches offer the feature, but there is plenty of other technology that aims to identify and track sleep habits, too, including pads that slip under your mattress or sheets, finger rings, special earbuds, headbands or bedside devices.
Depending on the device, a sleep tracker gathers information on the number of sleep cycles you go through, the length of your deep sleep and REM sleep stages, heart rate, blood oxygen saturation, breathing and temperature, among other data points.
But do sleep trackers work? When it comes to serious sleeping disorders, experts say sleep trackers are no match for an official sleep study recommended by a doctor. Research suggests sleep trackers overestimate total sleep time and underestimate the time it takes to fall asleep.
But experts also say sleep trackers can help people get a general idea of their overall sleep patterns or sleep habits. And that may be enough to spur them to make changes to improve it.
The best way to get more deep sleep and REM sleep is to get more quality sleep in general. That means focusing on some lifestyle changes that lead to regular nights of uninterrupted Zs.
Some general tips to improve sleep include paying attention to what you eat and drink later in the day to avoid caffeine or other things that can disrupt your sleep. Creating an ideal sleeping environment. Establishing a calming bedtime routine and a consistent sleep schedule. Slotting your workouts for earlier in the day. And considering products that can help you relax so you are able to fall asleep, like sleep gummies or another sleep supplement.
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