The 5 Cycles of Sleep Explained
Do you have a hard time sleeping, falling asleep or lie awake at night worrying you’re not getting enough sleep?
You’re not alone! We are in the middle of a sleepless epidemic, which has the potential to damage people’s health, productivity and happiness.
If everyone in the US who sleeps fewer than six hours a night got between six and seven hours, there would be a $226 billion boost to the economy. Just from getting an extra hour or two of good sleep. Thi9nk about that. Read it again.
Sleep is a vital basic need during which important processes in the body are completed. While we are sleeping our body repairs and regenerates. It also stabilizes our immune system, repairs cells and processes the day’s new information, setting it into long-term memories while we are sleeping.
Development and Function
Sufficient and healthy sleep is essential to our well-being, important for recovery and performance. Sadly, restful sleep does not always occur naturally. Many people around the world suffer from sleep disorders that not only massively inhibit quality of life, but can also lead to health problems.
Science has long recognized that melatonin, a neural hormone which is distributed at night plays a significant role in the regulation of our circadian rhythm, is necessary in order to find good and healthy sleep. Melatonin is produced in the pineal gland of the brain and controls our inner clock, stimulates the activity of numerous cell groups and regulates our sleep.
Additionally, this hormone possesses an antioxidant effect. If melatonin production is disturbed, or if not enough of the hormone is being produced or distributed at the correct time, then our sleep is impaired, which can lead to weight gain and a number of different illnesses.
Sleep Phases
At night our body goes through a number of sleep phases:
These sleep phases are passed through multiple times in one night. After REM sleep, the body falls back into light sleep and the sleep stages begin again. Each cycle lasts approximately 90 minutes.
Five phases of sleep
During sleep, we usually pass through five phases of sleep: stages 1, 2, 3, 4, and REM (rapid eye movement) sleep. These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1. We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep.
- Stage 1
Which is light sleep, falling asleep is a transitional period between being awake and sleeping, the body starts to rest, blood pressure, pulse and breathing becomes slower - We drift in and out of sleep and can be awakened easily. Our eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images.
- Many also experience sudden muscle contractions often feeling a sensation of falling. These sudden movements are similar to the “jump” we make when startled.
- Stage 2
We are creating relaxation of muscles, our eye movements stop and our brain waves become slower, with occasional bursts of rapid waves - Stage 3
Extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster waves. - Stage 4
Is where actual regeneration takes place, the brain produces delta waves almost exclusively. It is very difficult to wake someone during stages 3 and 4, which together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. Some children experience bedwetting, night terrors, or sleepwalking during deep sleep. - REM sleep
When we switch into REM sleep, rapid eye movement, the brain is unusually active and in dream phase where we process memories
Our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed. Our heart rate increases, our blood pressure rises, and males develop penile erections. When people awaken during REM sleep, they often describe bizarre and illogical dreams.
The first REM sleep period usually occurs about 70 to 90 minutes after we fall asleep. A complete sleep cycle takes 90 to 110 minutes on average. The first sleep cycles each night contain relatively short REM periods and long periods of deep sleep.
As the night progresses, REM sleep periods increase in length while deep sleep decreases. By morning, people spend nearly all their sleep time in stages 1, 2, and REM.
People awakened after sleeping more than a few minutes are usually unable to recall the last few minutes before they fell asleep.
This sleep-related form of amnesia is the reason people often forget telephone calls or conversations they’ve had in the middle of the night. It also explains why we often do not remember our alarms ringing in the morning if we go right back to sleep after turning them off.
Dreaming and REM Sleep
We typically spend more than 2 hours each night dreaming. Scientists do not know much about how or why we dream. Sigmund Freud, who greatly influenced the field of psychology, believed dreaming was a “safety valve” for unconscious desires. The strange, illogical experiences we call dreams almost always occur during REM sleep.
REM sleep begins with signals from an area at the base of the brain called the pons These signals travel to a brain region called the thalamus , which relays them to the cerebral cortex – the outer layer of the brain that is responsible for learning, thinking, and organizing information.
The pons also sends signals that shut off neurons in the spinal cord, causing temporary paralysis of the limb muscles. If something interferes with this paralysis, people will begin to physically “act out” their dreams – a rare, dangerous problem called REM sleep behavior disorder.
A person dreaming about a ball game, for example, may run headlong into furniture or blindly strike someone sleeping nearby while trying to catch a ball in the dream.
REM sleep stimulates the brain regions used in learning. Like deep sleep, REM sleep is associated with increased production of proteins. One study found that REM sleep affects learning of certain mental skills. People who were taught a skill and then deprived of non-REM sleep could recall what they had learned after sleeping, while people deprived of REM sleep could not.
Sleep influenced by food, medications, chemicals, temperature
Since sleep and wakefulness are influenced by different neurotransmitter signals in the brain, foods and medicines that change the balance of these signals affect whether we feel alert or drowsy and how well we sleep.
- Caffeinated drinks such as coffee and drugs such as diet pills and decongestants stimulate some parts of the brain and can cause insomnia, or an inability to sleep.
- Many antidepressants suppress REM sleep.
- Heavy smokers often sleep very lightly and have reduced amounts of REM sleep. They also tend to wake up after 3 or 4 hours of sleep due to nicotine withdrawal.
Many people who suffer from insomnia try to solve the problem with alcohol – the so-called night cap. While alcohol does help people fall into light sleep, it also robs them of REM and the deeper, more restorative stages of sleep. Instead, it keeps them in the lighter stages of sleep, from which they can be awakened easily.
People lose some of the ability to regulate their body temperature during REM, so abnormally hot or cold temperatures in the environment can disrupt this stage of sleep.
If our REM sleep is disrupted one night, our bodies don’t follow the normal sleep cycle progression the next time we doze off. Instead, we often slip directly into REM sleep and go through extended periods of REM until we “catch up” on this stage of sleep.
People who are under anesthesia or in a coma are often said to be asleep. However, people in these conditions cannot be awakened and do not produce the complex, active brain wave patterns seen in normal sleep. Instead, their brain waves are very slow and weak, sometimes all but undetectable.
Sleep Disorders and Their Frequency
While children and babies require large amounts of sleep (infants require 16 or more hours), the average length of sleep for adults is between 6 and 8 hours each night. Sleep behavior varies from person to person and is dependent on chronotype (owl = night person, lark = morning person). A sleep disorder is present if a person receives less than 6-7 hours of sleep every night for a time period of at least 6 months.
20 to 30 percent of humans suffer from sleep disturbances, with men and women suffering equally. In those over the age of 65, the number grows to 70 to 80 percent. Only a third of these (30-35 percent) visit a doctor because of this. Around 70 percent of those suffering from sleep problems are prescribed a sleep aid such as benzodiazepine, while 30 percent are self-medicated (f.e. through the help of antihistamines).
“Too little sleep makes one dumb, fat and sick.” A bold statement which sadly is grounded in truth. Insufficient sleep causes a number of mental and physical illnesses.
Effect on Memory
What we learn during the day is solidified while we sleep (sleep associated memory consolidation). Those who suffer permanently from lack of sleep will have to count on decreased memory capability. Numerous studies have found this to be true. Sleep disorders contribute to the limitation of memory formation, leading to forgetfulness, difficulty concentrating and overall performance reduction.
Effect on Weight
Those who sleep too little also show an increased risk for obesity. Lack of sleep means that we are awake longer, which can lead to poor habits such as watching TV and playing on the computer that require less movement and cause us to run to the refrigerator late at night for an unhealthy snack. Late at night we are especially prone to enjoy calorie rich foods. Studies have shown that people who sleep less eat more than those who sleep enough. Lack of sleep can lead to increased appetite, which finally leads to weight gain. Hormone changes that are triggered through missing sleep are responsible for this. Even if we do not eat too much, but eat more at night, then the ingested calories are more likely to be saved as fat.
Effect on Mental Health
It is not uncommon for mental illnesses to be fostered through permanent lack of sleep. In not-so-serious cases this is expressed through constant tiredness, irritability, lack of motivation and mood swings. In the worst cases it can result in hallucinations or depression. These disturbances can appear when the brain is overburdened due to a sleep deficit, especially if a predisposition of mental illness is present.
Effect on Physical Health
Too little sleep has negative consequences for our immune system. This encourages the development of illnesses that can take the form of harmless colds or flu symptoms. However, long-term sleep disturbances can lead to serious health problems. Chronic sleep disturbances on an average of three out of seven nights can increase the chances for gastrointestinal ailments, heart attack stroke, diabetes, vascular diseases and even cancer.
A study conducted by the European Heart Journal found that the risk for heart disease increases by 48 percent if we consistently sleep less than six hours. Other studies have proven that sleep deprivation can lead to high blood pressure, clogging of the arteries and heart failure.
One study from Japan also showed a connection between sleep disorders and diabetes. It was able to determine that a heightened long-term blood sugar level showed a clear correlation with problems sleeping through the night and waking up too early in the morning. It is suspected that poor sleep causes the release of stress hormones (i.e. cortisol) which favor the development of diabetes.
Last but not least, insufficient sleep can also trigger cancer. People who can ascribe their sleep disorders to shift work show an especially high risk. In 2007 the International Cancer Research Center of the WHO classified nightly shift work as “probably carcinogenic.” A heightened risk for cancer was especially found in hospital personnel and flight attendants, since the permanent displacement of the biological sleep-wake order and the use of artificial light encourages the development of tumors.
Health-supporting, quality sleep involves five sleep cycle stages that repeat throughout the sleep period. However, in today’s fast-paced, always-connected world, it has become all too common to neglect sleep. Insufficient sleep and sleep cycle disruption can hold serious consequences for productivity cognitive function and overall health.
Insufficient sleep has become such a widespread problem that health officials have deemed it to be a public health threat. This is because of the way it disrupts the fundamental regulating systems of the body, including the circadian rhythm. Circadian rhythm disruption is connected to a wide range of health issues and chronic diseases. Insufficient sleep is associated with an increased risk of type 2 diabetes, obesity and cardiovascular disease, all of which are also associated with metabolic system disruption.
High blood pressure, heart disease, stroke, obstructive sleep apnea (OSA) and other respiratory issues are also connected to insufficient and poor quality sleep. So, too, are poor memory function, decreased concentration, reduced ability to perform complex mental tasks and an increased risk of depression and mood disorders. For optimal physical health and cognitive performance, it’s essential to get enough sleep and to reduce the disruption of the sleep cycle stages.
Transitioning From Wakefulness To Sleep
The first stage of sleep begins the process of easing the mind and body from wakefulness into sleep. In this stage, breathing begins to slow and becomes more regular as the brain starts shifting away from beta waves to slower alpha and more meditative theta waves. The muscles start to become less active, and the heart rate decreases.
During this period of slowing muscular activity, there can be occasional muscle twitches, leading to the common sensation of falling that can jerk a person nearly back to full wakefulness. In this first sleep stage, waking is still easy, especially with environmental disturbances such as light or sound.
Eye movements cease during the second stage of sleep and breathing continues to deepen, becoming even more regular. Body temperature begins to decrease and the heart rate continues to decrease. Theta brain waves slow and there are periodic quick bursts of brain waves called sleep spindles While waking is still relatively easy during much of the second stage, the purpose of the second stage is to transition from light sleep to deep sleep, where much of the restorative work is done.
Deep, Restorative Sleep
Sleep stages three and four are the deep sleep cycles where vital body and brain maintenance take place. During stage three, delta waves begin to appear, soon transitioning to the full delta waves that characterize stage four sleep. Body temperature is at its lowest, heart rate is slowest and breathing is deepest and most regular during these stages of sleep. It can be difficult to wake someone in the deep stages of sleep, and when woken, that person is likely to be groggy for up to 30 minutes or so.
It is during deep sleep that physical healing takes place, along with the detoxification of the brain and the re-energizing of the immune system. Metabolic system balancing, including blood sugar and hormonal balancing, takes place during this period.
Memories and emotions including things learned and the day’s experiences, are processed and filed for later retrieval. Making up as much as 23 percent of a full night’s sleep, deep sleep is critical to health and well-being. The deep sleep stages are longer during the earlier cycle repetitions, growing shorter as the repeating cycles move towards the end of the sleep period.
REM Sleep Is A Category Of Its Own
Making up about 20 to 25 percent of a healthy night’s sleep, REM sleep differs from all of the other states. In REM sleep, the brain is almost as active as it is when awake. Breathing can be rapid and shallow. There’s plenty of eye movement, although the other muscles of the body are typically prevented from strong movement, aside from the occasional twitch. This is the dreaming stage, and the immobilization of the muscles keeps sleepers physically safe during their dreams. The REM stage also plays a role in memory consolidation.
Prioritize Sleep For Better Health
Newborns do not develop a circadian rhythm until they are a few months old. This can cause their sleeping patterns to be erratic in the first days, weeks, and months of their lives. Babies begin to release melatonin when they are about 3 months old, and the hormone cortisol develops from 2 months to 9 months old.
Toddlers and children have a fairly regulated sleep schedule once their circadian rhythm and body functions mature. Children need about 9 or 10 hours of sleep a night.
Toddlers need up to 14 hours of sleep daily. Young children should sleep up to 13 hours a day, and older children 12 hours. Teens need 8 to 10 hours of sleep per night, with adults ranging between 7 and 9 hours. This allows sufficient time for the optimal sleep stage repetition that is so essential to physical health and cognitive function.
Your circadian rhythm is your body’s natural way of keeping to its 24-hour body clock, helping your body operate on a healthy sleep-wake schedule. Living a healthy, active lifestyle that promotes proper rest will help you maintain your body, your memories and live a long healthy life.
Your mouth gives you warning signs. Are you listening?
Resources:
https://www.chronobiology.com/the-five-sleep-cycle-stages-explained/
https://www.upmc.com/services/pulmonology/our-services/sleep-medicine/resources/during-sleep
https://www.healthline.com/health/healthy-sleep/circadian-rhythm#in-babies
