Sleep varies, but healthy adults need between seven and nine hours of sleep per night to function at their best. On the other hand, children need 12 hours of sleep to ensure proper growth. But is it the quantity of sleep that matters, or the quality?
The short answer is both. The quality of sleep you get is directly related to the quantity of sleep you get because you experience many stages of sleep throughout the night in cycles. When you cut a cycle short, your body has to restart, which means you’re losing out on quality sleep, too.
What Are The Stages of Sleep?
There are four stages of sleep that your brain experiences during a normal or healthy sleep cycle. These four stages of sleep fall into two categories: rapid eye movement (REM) sleep and non-REM (NREM) sleep.
Here’s a breakdown of the stages of sleep:
NREM Sleep
The first cycle of sleep is NREM sleep. NREM sleep is a resting state in which your brain is transitioning from consciousness to deep sleep, where the restorative process begins. NREM sleep consists of three different stages:
Stage one (N1). In this first stage, brain activity slows and your muscles begin to relax. Your eyelids feel heavy and you start to nod off.
Stage two (N2). In the second stage, you enter into a light sleep. Brain activity continues to slow down and your heart rate and temperature begin to drop. This dreamless stage of sleep is easy to wake from.
Stages three & four (N3). The N3 stage of sleep is when the restorative process begins as your mind and body begin building up energy. This stage is where deep sleep occurs.
REM Sleep
The second cycle of sleep is REM sleep. According to the National Sleep Foundation, “REM sleep is an active period of sleep marked by intense brain activity. Brain waves are fast and desynchronized, like those in the waking state. Breathing becomes more rapid, irregular, and shallow; eyes move rapidly in various directions and limb muscles become temporarily paralyzed. Heart rate increases and blood pressure rises. This also is the sleep stage in which most dreams occur.”
How Much Deep Sleep Should You Get In A Night?
Adults need anywhere from 90 minutes to two hours of deep sleep per night, which is approximately 20-25% of your overall time spent sleeping. Some people may require more deep sleep in order to feel fully rested, so it's important to understand that every individual is unique.
Regardless, deep sleep is the beginning of your body's restorative process and crucial to good sleep health. Your mind and body regenerate during this stage of sleep, so it is important to both your physical and mental health that you get enough deep sleep.
Neurological Effects Of Deep Sleep
Deep sleep is responsible for the neural stimulation necessary to develop mature neural connections. To be in a deep sleep means to be in the N3 stage of NREM sleep, also known as slow-wave sleep.
Slow-wave sleep is the deepest stage of NREM sleep because your brain is less responsive to external stimuli due to the presence of low-frequency delta waves.
Physical Effects Of Deep Sleep
Deep sleep leads to short- and long-term memory consolidation, increased coping skills, boosted metabolism, emotional processing, muscle recovery, balanced blood sugar levels, and a stronger immune system.
How Often Does Deep Sleep Occur Throughout The Night?
A person with no sleep problems should experience deep sleep up to five times per night. However, many people have trouble staying asleep, which prevents the brain from entering the deep sleep stage. Scientists refer to this type of disrupted sleep as sleep fragmentation.
Why Do You Wake Up So Tired?
Your mind and body are easily affected by lack of quality sleep. There are many factors that can disturb your normal sleep cycle by reducing the amount of N3 and REM sleep you achieve. Without an adequate amount of deep sleep, you wake up feeling tired and unrefreshed, which can take a toll on you mentally and physically throughout the day.
Several internal factors such as sleep apnea, insomnia, chronic pain, stress and anxiety can hinder your ability to achieve deep sleep. If you think you suffer from a sleep disorder, contact your healthcare professional to find a solution.
There are also several external factors that can negatively affect your sleep cycle. Here are some of the most common contributors to sleep fragmentation:
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Light. Light is one of the most powerful external influences on sleep. Your natural circadian rhythm coincides with light exposure; sunlight (or lack thereof) distinguishes day from night, which is how your body knows when it’s time to sleep. In today’s digital age, your body is exposed to greater amounts of light for longer periods of time, most notably from screens like laptops and cellphones.
Exposure to light in the evening can delay your internal clock because light signals to your brain that it’s still day and not time for sleep yet. This can cause you to stay awake for longer, which means you won’t get enough sleep throughout the night. The less sleep you get, the less time you spend in deep sleep.
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Caffeine and other stimulants. Stimulants by nature are supposed to keep you awake — that’s why most people reach for that cup of coffee in the morning. Consumption of caffeine and other stimulants should be minimized as the day draws to a close.
Even if you’re someone who has a high tolerance for caffeine, your sleep cycle will be affected if you consume stimulants too close to bedtime. Caffeine decreases the amount of time spent in slow-wave and REM sleep and increases the likelihood of waking up throughout the night.
- Alcohol. Since alcohol is a depressant, it often helps people fall asleep faster. However, the quality of sleep you can achieve is compromised when alcohol is present in the body. Like caffeine, alcohol can hinder your brain’s ability to enter the slow-wave and REM sleep stages, which means you’re more likely to wake up throughout the night.
What Happens When You Don’t Get Enough Sleep?
Deep sleep triggers the restorative process — tissue repair occurs, your body detoxifies itself and your brain is able to slow down. According to the American Sleep Association, “Activity in parts of the brain that control emotions, decision-making processes, and social interactions is drastically reduced during deep sleep, suggesting that this type of sleep may help people maintain optimal emotional and social functioning while they are awake.”
When you don’t get enough deep sleep, your brain is unable to refresh, so you’re likely to wake up feeling irritable and fatigued. Most adults need 7 or 8 hours of sleep each night to feel well-rested.
Side Effects Of Sleep Deprivation
Lack of sleep causes sleep deprivation, which can be dangerous. Minor side effects of sleep deprivation include weight gain, poor balance, mood swings, and decreased performance at work or in academics.
However, these minor side effects can lead to more serious consequences. Compromised concentration and delayed reflexes lead to accidents and injury. According to the National Highway Traffic Safety Administration, “...in 2015, over 72,000 police-reported crashes involved drowsy drivers. These crashes led to 41,000 injuries and more than 800 deaths.”
Lack of sleep can also cause serious health problems, including depression, obesity, heart disease, and Type 2 diabetes.
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