In general, we tend to think of sleep as a binary: you’re either asleep or you’re awake. Yet the reality is far more complex and fascinating. Sleep consists of four distinct phases, all of which are essential to short-term energy and long-term health.
In this post, we’ll take a look at each of the stages, examine how they affect your health and explore ways that you can optimize each stage of sleep in order to improve your overall health and well-being.
Why Sleep Matters
Sleep researchers have yet to fully understand sleep, but we do know that not getting enough of it can have serious effects on your energy and health. In the short term, sleep deprivation harms your cognitive and fine-motor abilities, resulting in a state very similar to drunkenness (particularly if you go more than 17 hours without sleeping).
Over the longer term, chronic lack of sleep can lead to increased weight gain and anxiety levels, plus higher risk of stroke and getting sick. Not to mention, you’ve likely experienced the increased irritability and lack of focus that comes from sleep deprivation.
This is why getting between seven to nine hours of sleep (the recommended amount for adults according to the National Sleep Foundation) is crucial. Trading sleep for increased work hours is a false economy: in the end you’re only harming your health and your productivity.
But as you’ll see in the following sections, it’s about more than getting “enough” sleep. Your sleep also needs to be high quality, and much of that comes from understanding (and optimizing) the different phases that make up the sleep cycle.
Understanding the Sleep Cycle
Sleep is not just one long, continuous period of being “not awake.” Rather, it’s composed of four distinct stages, all of which play a role in repairing your body, consolidating your memories and overall helping you feel well-rested.
Furthermore, you don’t just move through each stage once. Rather, sleep is cyclical: In the course of a night, you shift between the different stages. This is another reason getting enough sleep is so important. When you sleep less than you should, you deprive your body of the full range of necessary sleep stages. Note that your individual sleep needs may vary based on your activity levels, age, and health.
But what are the different sleep stages? And how much time does your body spend in each one?
Broadly, we can divide sleep into two main types: REM-sleep (rapid eye movement sleep) and non-REM sleep. Non-REM sleep also breaks down into three further stages, which we’ll explore next.
The 3 Stages of Non-REM Sleep
Non-REM sleep consists of three stages: Light Sleep Stage 1, 2, and Deep Sleep.
Let’s look at them in detail.
Stage 1 & 2: Light Sleep
Light sleep is the state you experience when you’re first falling asleep. It’s a very light phase of sleep, only lasting a few minutes. Still, the state of your body in this stage differs from when you’re awake. Your heart rate, breathing, eye movements, and brain waves all slow down as you gradually transition from wakefulness into sleep.
In terms of physiology, this phase is most important for its role in transitioning you into the more restorative phases of sleep. Therefore, an inability to reach this phase can be frustrating and detrimental. To help improve your ability to reach this stage, check out our guide to falling asleep faster or our introduction to meditation for sleep.
After light sleep, there comes deeper sleep. In many ways, this stage is similar to Stage 1. Your breathing and heart rate become even slower along with your brain activity. Muscle relaxation also increases, and eye movements stop completely. Your body temperature also drops.
While this is the second stage of sleep you enter, it won’t be the last time during the sleep cycle that you experience it. In fact, your body spends more of its sleep time in this stage than in any other. It also plays an important role in your mental health — research suggests that Stage 2 sleep plays a role in long-term memory consolidation, which is critical for helping you learn new things.
It’s still relatively easy to awake during this phase. Therefore, if you’re having trouble staying asleep, it could be due to disturbances during this stage. Try wearing earplugs and an eye mask to ensure that sudden bright lights or noises don’t jolt you back awake while you’re still drifting off into the deeper sleep phases.
Stage 3: Deep Sleep
Finally, we come to the last stage of non-REM sleep. Deep sleep reaches its longest periods during the first half of the night. The characteristics of the previous two sleep stages intensify even further: Your breathing and heartbeat reach the lowest levels of the sleep cycle, and your brain waves reach their slowest as well. Your muscles become even more relaxed, and it’s difficult for others to awake you.
Deep sleep is crucial for muscle growth and physical recovery, as it’s during this stage that the brain secretes high levels of human growth hormone. The brain also repairs itself during this stage. Brain wave activity decreases, so the brain has time to recover from the work of the day. Overall, deep sleep is necessary for feeling well-rested and restored in the morning; not getting enough of it can leave you groggy despite having slept for seven to nine hours.
To boost your amount of deep sleep, one option is to increase the amount (and intensity) of your exercise regimen. A study published in “Science” showed that prolonged periods of strenuous exercise are correlated with greater amounts of deep sleep. More deep sleep is necessary in order to help your body recover. This is also why it’s so important to get more sleep while training for a marathon or other athletic activity.
Now that we’ve covered the three stages of non-REM sleep, we can move to Stage 4: REM sleep. You generally reach the first cycle of REM sleep about 90 minutes after falling asleep, and you’ll return to REM sleep several times during the night.
In the REM stage, your brain and body become markedly more active compared to non-REM sleep. To start, your heart rate and blood pressure increase, while your breathing becomes fast and irregular. While your eyelids remain closed, your eyes move back and forth rapidly. Your brain activity also increases, reaching levels near that of when you’re awake. For this reason, REM sleep is sometimes called “paradoxical sleep.”
Despite all this, you experience muscle paralysis in your arms and legs, which is a good thing, considering that you also experience your most vivid dreams during the REM period. If your arms and legs weren’t paralyzed, then you would run the risk of acting out your dreams (something you realize could be problematic if you’ve ever had a dream where you’re running, flying, or fighting a giant monster).
Unlike non-REM sleep, scientists disagree on the purpose of REM sleep. For instance, scientists have done studies in which they woke their subjects when their brain activity (as measured using an EEG, or electroencephalogram) indicated that they were in REM sleep.
Despite doing this repeatedly over the course of the study, the subjects displayed no adverse effects in terms of their restfulness or overall health. This research seems to indicate that REM sleep has no clear purpose, at least when it comes to the functioning of the body.
More recent research has suggested a possible link between REM sleep and the consolidation of emotional memories. When a memory has a strong emotional component, it tends to be more vivid. There is possible evolutionary support for this idea, as remembering strongly negative situations (particularly dangerous ones) helps you survive and ultimately pass on your genes. REM sleep, then, could help to prioritize the consolidation of emotionally charged memories over more neutral ones, thus helping you better respond to threats in the future.
Still, the precise role of REM sleep is unclear, and further research is necessary to give more definite answers.
How to Improve the Quality of Your Sleep
Now that you understand the different phases of sleep, let’s take a look at some ways to improve the overall quality of your sleep.
1. Avoid Drinking Alcohol Before Bed
Drinking alcohol might seem like a good way to help yourself fall asleep. Alcohol is a depressant, which means that it will make you feel sleepy and relaxed. But while alcohol does produce temporary feelings of drowsiness, it ultimately impedes your ability to sleep. It can interrupt your circadian rhythm, which is the natural cycle by which your body regulates sleeping and wakefulness. This can lead your brain to think you should be awake even when it’s the middle of the night.
Furthermore, since alcohol is a diuretic, it can lead you to wake up in the middle of the night having to urinate. While this may be a normal nighttime occurrence for some people (especially older adults), alcohol use before bedtime can exacerbate it.
2. Stop Consuming Caffeine at Least 6 Hours Before Bed
Caffeine is a miracle drug, allowing us to stay awake when we might otherwise be unable or giving us the extra little boost of energy necessary to finish a big project. But if you consume caffeine too close to bedtime, its energy-boosting effects can harm your ability to fall (and stay) asleep.
According to a study published in the Journal of Clinical Sleep Medicine, consuming caffeine up to six hours before you go to bed can disrupt your sleep. Therefore, it’s best to stop drinking coffee, tea, or whatever other caffeinated beverages you consume at least six hours before you want to fall asleep. Of course, this will vary based on your personal bedtime, and you should experiment to see how different timings or amounts of caffeine affect your sleep.
3. Start Eating Foods That Help You Sleep
While caffeine and alcohol can disrupt your sleep, there are also foods you can eat that will help boost your sleep. Walnuts, prunes, cheese, and honey are just a few of the foods that can help you get a better night’s sleep, all while maintaining a tasty, balanced diet. For more foods that will help you sleep, check out our guide.
4. Get Enough Exercise
According to a paper published in the Journal of Clinical Sports Medicine, exercise can be an effective treatment for insomnia. Because exercise depletes energy stores, breaks down body tissue, and elevates body temperature, it can be a powerful stimulus for sleep (since sleep works to replenish energy, repair body tissue, and lower body temperature).
The precise type of exercise you get isn’t important. You should choose an activity that you enjoy and will actually stick with. Maybe that’s a popular form of exercise such as running, or maybe it’s something more unconventional such as rock climbing.
That being said, aim for strenuous exercise that elevates your heart rate, makes you break a sweat, and leaves you feeling tired afterwards. Light exercise such as walking is certainly beneficial, but the research on sleep and exercise seems to suggest that strenuous exercise is more effective in promoting improved sleep.
The Mayo Clinic recommends at least 30 minutes of physical activity per day (though you may want to increase that if you’re attempting to lose weight or train for an athletic event). To see if the exercise is vigorous enough, you can use a tool such as the Spire Stone to help monitor your breathing while exercising.
5. Talk to a Doctor About Possible Medical Conditions
In many cases, improving your sleep is just a matter of making some simple lifestyle and environmental changes, as we’ve discussed so far. But in some cases, difficulties sleeping could be the result of more serious medical conditions.
For instance, if you find yourself having trouble sleeping until late at night (and then sleep till the afternoon), you could be suffering from delayed sleep phase disorder. If you wake up drowsy even after sleeping a full night, you could have sleep apnea (a condition in which you stop breathing for short periods while you’re asleep).
Any difficulty sleeping is always worth discussing with your doctor, as they can provide you advice on possible further steps to diagnose and treat sleep disorders.
6. Track Your Sleep with a Wearable Device
Understanding the different phases of sleep gives you a solid start on how to improve the quality of your sleep, but this information is even more powerful if you can see it in action. One of the best ways to do this is to use a wearable device to track your breathing, heart rate, and activity while you sleep.
Enter the Spire Health Tag: a tiny wearable device that fits into your life and syncs with your phone. You can see how much time you spend in each of the different sleep phases as well as the overall quality of your sleep. With this information, you can take appropriate steps to improve you sleep (or decide if you should talk to a medical professional for further help).
Check out the Spire Health Tag to get started.
As you can now see, sleep is far more than just the time when you’re not awake. It’s essential to proper brain and body functioning, and it’s composed of several distinct stages. With proper nutrition, limiting the consumption of certain substances, and limiting blue light exposure, you can dramatically improve the quality of your sleep.
Still, you should always talk to a doctor if you have any serious concerns about your ability to fall or stay asleep, as these could be signs of a more serious health problem. The advice in this article is just general guidelines to help you understand and improve your sleep; it is not a substitute for professional medical advice.