What is Sleep? Sleep Cycle, and How Much Sleep Do You Need
What is sleep?
Sleep is a vital physiological process that allows the mind and body to rest, heal, and repair. In humans, it corresponds to a basic body posture, such as lying down and closing one's eyes.
Sleep occurs as a repetitive cycle of different stages. During sleep, muscle activity and interactions with the surrounding environment decrease remarkably. This is when the body and brain have adequate time for healing and regrowth and performing vital tasks like releasing essential hormones and removing toxins.
It is crucial to understand that proper sleep is not just a luxury. Still, it is essential for various bodily functions, such as enhancing brain and cognitive functions, promoting growth and healing, conserving energy, and facilitating learning and memory consolidation.
It helps optimize the cardiovascular and immune systems and restores and repairs cells. Also, it regulates emotional well-being and hormones, helps in weight maintenance, detoxifies the body, and reduces oxidative stress. Thus, prioritizing sleep can ensure that all these physiological processes work optimally, leading to better health and well-being.
Moreover, studies reveal that prolonged sleep deprivation or inadequate quality of sleep can lead to health problems such as high blood pressure, heart disease, diabetes, depression, and obesity.
Sleep Cycle
When you sleep, you can feel that you are sometimes awake and other times in a much deeper sleep. What are these instances that we experience?
A sleep cycle, a fascinating process, is broadly divided into two main types: Non-REM (Rapid Eye Movement) sleep and REM sleep. The non-REM (NREM) stage is divided into three different stages, ranging from light (stage 1) to intermediate (stage 2) to deep sleep (stage 3). The last sleep cycle is REM sleep (stage 4). All four stages repeat several times during a typical night.
If you wake up during REM sleep or the REM sleep ends, you start again at stage 1 or 2 (non-REM sleep), and the cycle repeats itself throughout the night. On a typical night of eight hours of sleep, each cycle lasts around 90 to 120 minutes, and you'll go through four or five cycles during this sleep period. Let's understand each stage in detail in the following section.
NREM Stage 1: Light sleep
Duration: 1 - 7 minutes
It is the initial stage of the sleep cycle, from being awake to moving into sleep, and it lasts only a few minutes. It contributes to 5% of your sleep time. In this stage, your sleep is very light, and you can still be easily woken up.
During this light sleep, muscles start to relax, and brain activity, breathing, heartbeat, and eye movements start to slow down.
NREM Stage 2: Intermediate sleep
Duration: 10- 25 minutes
It is the stage between light and deep sleep. In this stage, your heartbeat and breathing slow down further, and your eye movements stop. Also, muscles continue to relax, and body temperature drops slowly.
During your entire sleep, you spend the most time in stage 2, comprising about 45% of your sleep time. After stage 2, you will move into stage 3 or can enter directly into REM sleep. Moreover, you will go through multiple rounds of stage 2, and each one is longer than the last.
NREM Stage 3: Deep sleep or Slow-wave sleep
Duration: 20-40 minutes
After deep sleep (Stage 3), you enter into REM sleep. It usually occurs about every 90 minutes after falling asleep, making up about 20-25% of your sleep cycle. Your heartbeat and breathing increase and become regular to waking levels.
Your immune system is strengthened, and your body repairs any injuries during this stage. Moreover, your muscles are relaxed, and your heartbeat and breathing slow down to their lowest level.
Stage 4: REM Sleep
Duration: 20-40 minutes
After deep sleep (Stage 3), you enter into REM sleep. It usually occurs about every 90 minutes after falling asleep and makes up about 20-25% of your entire sleep cycle. Your heartbeat and breathing increase and become regular to waking levels.
Your eye moves (side to side) rapidly behind your eyelids, hence the name rapid eye movement. This stage is where the brain removes all toxins and byproducts. Memory consolidation or restoration, mood regulation, and much learning also occur here.
Typically, you dream in REM sleep and become temporarily paralyzed, i.e., you cannot move your hands and legs in this sleep stage. Moreover, your first REM cycle is typically around 10 minutes, and the one that follows is longer than the previous one, up to an hour.
During a typical sleep cycle of 8 hours, an inpidual spends around 90 minutes to 2 hours in REM sleep. However, the time spent in REM sleep declines as you age.
How Much Sleep Do You Need? Let's find out.
The quantity and quality of sleep you need depends on various factors, such as age, lifestyle, activity level, and overall health. According to the National Sleep Foundation, sleep duration also varies from person to person of the same age. Some individuals might sleep longer or shorter than the recommended times with no adverse effects. The following are the recommendations of sleep duration based on age group.
- Newborns (0 - 3 months): 14 - 17 hours
- Infants (4 - 12 months): 12 - 16 hours (including naps)
- Toddlers (1 - 2 years): 11 - 14 hours (including naps)
- Preschoolers (3 - 5 years): 10 - 13 hours (including naps)
- School-age children (6 - 13 years): 9 - 12 hours
- Teenagers (14 - 17 years): 8 - 10 hours
- Adults (18 - 64 years): 7 - 9 hours
- Older adults (65 years and older): 7 - 8 hours
Conclusion
To conclude, sleep is an essential process for our body and mind to rest, heal, and repair. There are two main types of sleep: Non-REM (Stage 1-3) and REM (Stage 4). Every inpidual goes through these stages multiple times during sleep. Moreover, the amount of sleep an individual needs depends on various parameters. However, not getting enough sleep can cause serious health problems.
