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We all wait for the night to get the well-deserved rest our body needs after a long and tiring day!
And that rest comes in the form of sleep. In fact, just like food and water, sleep is crucial to our survival. But what most of us don't know is that when we sleep, our body passes through four sleep stages that cycle four to five times throughout the night.
Several biological processes occur during these sleep cycle stages to help the body cells repair, restore energy, etc. These biological processes are necessary to help us function productively.
That's what this comprehensive guide is all about. We'll explain the importance of sleep, elaborate on the different sleep cycle stages, and provide a few tips to ensure quality sleep.
So, keep reading to know more!
Before we dive into the different sleep cycle stages, let's understand the importance of sleep in our daily life:
When in deep sleep, the body releases a growth hormone that supports growth in children and adolescents. It also produces a higher number of proteins responsible for cell growth and repair.
Insufficient sleep may compromise the immune system, making you prone to illnesses. In fact, people who suffer from chronic sleep deprivation have a higher risk of developing heart problems, diabetes, and obesity. As such, deprivation of REM sleep may also shorten one's lifespan.
Insufficient sleep can affect our performance, productivity, memory, and rational thinking capabilities. Moreover, if a person hasn't been getting good quality sleep, they might experience hallucinations, mood swings, and other neurological problems.
Sleep quality is a crucial factor that helps strengthen one's thinking capability and the brain's electrical activity.
Your brain cycles through four different sleep stages while you're asleep. The first three stages refer to Non-REM (NREM) or non-rapid eye movement sleep. And the last stage is REM or rapid eye movement sleep, also commonly known as the active sleep stage.
Let's understand each of the four sleep stages in a bit more in detail:
Almost 75% of individuals spend the first half of the night in the NREM sleep stages. It comprises three stages; the first stage being the lightest sleep stage. And the last two stages are when one sleeps deeply. Read on to know more.
This is the non-REM sleep stage, when a person just begins to fall asleep. It can be easily identified by the presence of slow eye movements and muscle activity. In fact, you'll notice the entire body beginning to relax, and the brain activity begins to slow down from that of "wake."
Stage 1 of the non-REM sleep cycle lasts for around five to ten minutes and can be easily disrupted by even the slightest sound or movement. And every now and then, you might experience abrupt muscle spasms, hypnic jerks, or even the feeling of falling while drifting in and out of sleep.
During this stage, your body begins to enter the phase of deep sleep. The eye movements gradually stop, brain waves and heart rates become more regular, and the body temperature decreases.
Your entire body relaxes, but there may be occasional bursts of rapid brain wave activity, known as sleep spindles. Here's when the brain collects, begins processing, and then filters acquired memories of the previous day.
Individuals usually spend up to 50% of their total sleep time during the non-REM sleep stage 2. And it lasts for 20 minutes per sleep cycle.
The final NREM sleep stage is when you are in deep sleep, which is difficult to wake up from, irrespective of loud noises and surrounding activities. Here's when the brain waves are slow yet deep (also referred to as delta waves), and there's no muscle activity or eye movement. And if you are awoken somehow, you might feel disoriented and groggy for a couple of minutes.
Cell regeneration, tissue repair, and growth also occur during this slow-wave sleep stage.
REM or rapid eye movement sleep occurs approximately 90 minutes post falling asleep, lasting around ten minutes. But the duration of the stage in each sleep cycle will increase as the night progresses.
Moreover, the REM stage one experiences in their life will vary with age. For instance, the percentage of rapid eye movement sleep is highest during early childhood and gradually declines when one reaches early adulthood or adolescence. It will further decline as you grow older.
That said, you no longer are in deep sleep during this stage. In fact, the brain activity levels increase to what they usually are when awake. This is why you usually see intense dreams during the REM sleep stage. Luckily, your body becomes paralyzed of sorts so that you don't act out the dreams.
You also experience faster breathing, increased blood pressure, heart rate, and of course, rapid eye movement.
A sleep cycle is a transition through the different stages of sleep as the night progresses. Every individual usually begins their sleep cycle with the NREM sleep stage and ends with the REM sleep stage before progressing back to the NREM stage.
Now, a full sleep cycle is around 90 to 120 minutes long, so you are most likely to experience four to five sleep cycles per sleep time. However, it's important to note that the sleep cycle will not progress with each sleep stage in perfect sequence.
For a majority of people, the first sleep cycle begins with stage 1 of non-REM sleep. It's short in duration with the prevalence of awakenings but crucial to sleep cycles as it allows the body to enter stage 2 of NREM sleep, which lasts significantly longer.
As the night progresses, you'll reach stage 3 of non-REM sleep, which doesn't last as long as stage 2. For adults, the total sleep time in this restorative sleep stage is between 5% and 15%. But for children and adolescents, the duration is higher.
Stage 3 is followed by the first rapid eye movement (REM) sleep of the night that's short in duration. And the process is repeated starting with stages 1, 2, and 3 of non-REM sleep in no specific order before returning to REM sleep for longer durations of sleep time.
In fact, the time spent in each sleep stage keeps changing as the cycle repeats. But more on that later.
A person is in deep sleep during stage 3 of NREM sleep. The brain waves during this stage have a slow speed but large amplitude. As such, waking someone up when in deep sleep is quite difficult.
In fact, one may experience extensive sleep time in this stage of sleep if they've experienced sleep deprivation. But muscle activity is prevalent, which is how people can kick or punch while asleep. Even parasomnias like sleep talking, night terror, sleepwalking, and bedwetting can occur in stage 3.
Nonetheless, this is one of the most restorative stages of sleep that may reduce your sleep drive. For instance, you will be able to fall asleep at night if you take a short nap during the day. However, if the sleep duration is long enough to fall into a deep sleep, you'll find it difficult to fall asleep at night.
REM, being the most active stage of sleep, is when the most vivid dreams occur. The brain waves during this sleep cycle stage have a lower amplitude and high frequency than that seen in stages 2 and 3 of NREM sleep.
As per the National Sleep Foundation, an individual can dream around 4 to 6 times in one night. But most dreams are forgotten after waking up. You may remember your dreams only if you wake up during REM sleep.
Along with increased heart rates and blood pressure, brain activity also significantly increases in this stage, similar to the levels observed when awake. That's why REM sleep is accompanied by muscle paralysis or muscle atonia. This is a protective method of preventing people from acting out during their dreams.
It's also crucial to note that obstructive sleep apnea is probably the worst during REM sleep. This is because the muscles, even in the back of one's throat, are too relaxed to support normal breathing at this stage.
The brain chemicals or neurotransmitters are active even while we're asleep. They help nerves communicate and control whether a person is awake or asleep, depending on the neurons (nerve cells) they are acting on. For instance:
They turn off the signals responsible for keeping us awake. As such, they enable us to fall asleep.
These neurons are located at the point where the spinal cord and brain meet. And they produce norepinephrine and serotonin, which are neurotransmitters that keep the brain active while awake.
That said, sleep is still a relatively new field of study, and researchers are still trying to understand sleep and its effects. In fact, REM sleep was only discovered in 1953 after new machines and technology were developed to monitor brain activity. Earlier, people believed that brain activity ceased when asleep.
We've come a long way since then, with scientists now disapproving of the idea that REM sleep deprivation may lead to insanity. However, this can be a cause of clinical depression.
Your sleep cycle will be affected whenever you find it difficult to fall and stay asleep at night. The sleep cycle stage in progress will be cut short, and a sleep cycle might repeat before even finishing.
This can happen either occasionally or regularly due to several reasons, such as:
Age plays a crucial role in one's sleep cycle. Older adults tend to sleep lighter, and even the slightest noise or activity may wake them. In fact, on average, an older person may wake up three to four times a night. Sleep disorders like insomnia are also commonly attributed to older age groups.
People suffering from chronic pain conditions, such as arthritis and fibromyalgia, may struggle to fall asleep or remain asleep. Other health conditions like asthma, obesity, heart conditions, Parkinson's disease, and Alzheimer's disease also contribute to lack of sleep.
Those suffering from mental health conditions like depression, anxiety, and bipolar disorder don't get sufficient sleep. Even the medications (antidepressants) prescribed to treat such conditions interrupt the sleep cycle and decrease the REM sleep duration.
It's a known fact that too much caffeine can keep you up at night. In fact, it's a leading cause of insomnia (the inability to sleep). So, you should avoid coffee and other caffeinated beverages if you want to get a restful night's sleep.
While alcohol may help you fall into light sleep quickly, it decreases the possibility of deep sleep and REM sleep. Likewise, chain smokers sleep light with a shorter REM sleep duration as they tend to wake up every few hours because of experiencing nicotine withdrawal.
As you might already know, a person's sleep patterns change with age. So, let's take a closer look at how age impacts the sleep cycle.
Newborns don't have any distinct sleep waves. Their sleep cycle is categorized into active (similar to REM sleep), quiet (similar to NREM sleep), and intermediate sleep. They usually are in active sleep most of the time, which is why they wake up easily. This is crucial to ensure consistent and frequent feeding.
The distinctions of sleep stages become more prominent in this age. You can develop a sleeping routine for your infant comprising two to three naps in a day with the total duration being approximately 10 to 13 hours.
A sleep pattern is fully developed by the time a child reaches the age of one to three years. The average sleep duration is 9 to 10 hours a day, with the number of naps reducing to one. This nap is taken during the afternoon to ensure uninterrupted sleep during the night.
Toddlers usually spend 25% of their sleep time in deep sleep, with an equivalent time spent in REM sleep.
Children between 3 and 6 years of age have the same sleep time as a toddler, i.e., 9 to 10 hours per 24 hours. The time they spend in deep sleep is still high, but the afternoon naps reduce post four years of age.
The sleep duration for children between the ages of 6 and 12 years remains unchanged (9 to 10 hours in a 24-hour period). And almost 20 to 25% of the total duration is spent in deep sleep, which is crucial for overall growth and development.
Adolescents sleep for around 9 to 9.5 hours in 24 hours. Interestingly, physiological changes in the circadian rhythm during this age prompt late sleep onset. This is one of the main reasons why young adults prefer sleeping late and sleep-in in the mornings.
As one ages, there's a shift back in the circadian rhythm, so sleep onset becomes regular and early again. An older individual sleeps for 6.5 to 8 hours a day.
Not getting adequate sleep and not completing the cycle through the different sleep stages have both long-term and short-term consequences. Some of those consequences have been listed below:
Alterations in sleep patterns also lead to health issues, such as:
You need to practice healthy sleep habits if you wish to achieve good quality sleep on a typical night. On that note, here are some of the dos and don'ts to keep in mind:
Make sure you wake up and go to sleep at the same time. You should maintain a proper sleep schedule even during vacations and weekends.
Before sleeping, ensure that the pillows and bed are comfortable. Set the thermostat to a comfortable temperature and turn off any lights or loud music.
You should always sleep with a relaxed frame of mind without any worries about the next day. Read a book or take a nice warm bath instead to de-stress before hitting the bed.
If you've been having difficulty sleeping or are suffering from any sleep disorder, talk to a sleep specialist. They will suggest a treatment plan for the sleep disorder and help you get a good night's sleep.
While you can take a short nap of around 30 minutes, taking long naps post 3 pm is not the best idea.
Using your mobile phone, tablet, laptop, or any other gadget that emits blue light right before you sleep can mess with the production of melatonin. This is a hormone the body produces at night to help you feel drowsy and tired. It also helps maintain the circadian rhythms so that you sleep on time.
You must already know by now that nicotine, alcohol, and caffeine consumption can interfere with your sleep stages. These substances can cause sleep disorders and prevent you from getting sound sleep at night.
It's important that you get 7 to 9 hours of uninterrupted sleep every night to allow the four sleep cycle stages to benefit you. That said, you might not be getting the required amount of sleep if you've been experiencing any of the following symptoms:
If you experience any one or more of these symptoms, make sure you visit your healthcare provider.
To sum up, getting ample sleep every night is crucial to our overall health and well-being. It boosts memory, promotes growth, aids digestion, and enables tissue repair.
And as you already know, there are four stages of sleep - each having its own role to play in your sleep cycles. Just make sure you follow the above-mentioned tips and a healthy sleep schedule to ensure good sleep quality. This will help you wake up feeling well-rested and rejuvenated in the morning to carry out your daily chores without difficulty.
Also, in case you notice signs of sleep disorders like sleep apnea or insomnia, visit your health provider immediately to discuss the right treatment options.
That's all from our end for today. Do keep an eye out for more informative reads from us in the near future!
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