Sleep varies, but healthy adults need between seven and nine hours of sleep per night to function at their best. Children need about 12 hours 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 is directly related to the quantity because you experience many stages of sleep throughout the night in cycles. When you cut a cycle short, your body must restart, which means you lose 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 stages 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
NREM sleep is a resting state in which your brain transitions from consciousness to deep sleep, where restorative processes begin. It consists of three stages:
- Stage one (N1): Brain activity slows and muscles begin to relax. Your eyelids feel heavy, and you start to nod off.
- Stage two (N2): Light sleep. Brain activity slows further, heart rate and temperature drop. This stage is easy to wake from and is dreamless.
- Stage three & four (N3): Deep sleep. The restorative process begins as your mind and body build energy. This is crucial for physical and mental health.
REM Sleep
REM sleep is an active period marked by intense brain activity. 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 rapid, irregular, and shallow; eyes move rapidly, and limb muscles become temporarily paralyzed. Heart rate increases and blood pressure rises. Most dreams occur during REM sleep.”
How Much Deep Sleep Should You Get In A Night?
Adults need 90 minutes to two hours of deep sleep per night, about 20–25% of total sleep. Some individuals may require more deep sleep to feel fully rested. Deep sleep is essential for the body’s restorative processes.
Neurological Effects Of Deep Sleep
Deep sleep (N3 stage of NREM) allows neural stimulation necessary for mature brain connections. Slow-wave sleep is the deepest stage of NREM sleep, where the brain is less responsive to external stimuli due to delta waves.
Physical Effects Of Deep Sleep
Deep sleep promotes memory consolidation, emotional processing, muscle recovery, metabolism regulation, balanced blood sugar, and a stronger immune system.
Frequency of Deep Sleep
A healthy person experiences deep sleep up to five times per night. Sleep fragmentation, caused by difficulty staying asleep, prevents reaching deep sleep stages. Sleep fragmentation is a common sleep disruption.
Why Do You Wake Up So Tired?
Factors disrupting your normal sleep cycle can reduce deep and REM sleep, leaving you tired and unrefreshed. Internal factors include sleep apnea, insomnia, chronic pain, stress, and anxiety. External factors include:
- Light: Evening light exposure delays your internal clock, reducing deep sleep.
- Caffeine and other stimulants: Minimize intake close to bedtime to avoid disrupting slow-wave and REM sleep.
- Alcohol: Alcohol may help fall asleep faster but reduces sleep quality, preventing deep sleep.
What Happens When You Don’t Get Enough Sleep?
Without sufficient deep sleep, your brain cannot refresh, leaving you fatigued and irritable. Most adults need 7–8 hours of sleep each night.
Side Effects Of Sleep Deprivation
Lack of sleep can lead to poor balance, mood swings, decreased performance, accidents, and injury. Long-term consequences include depression, obesity, heart disease, and Type 2 diabetes.
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