Have you wondered why sometimes is it more difficult to be woken up at around 2 am than maybe around 11 pm? Why do you feel groggy when you wake up at that time? The answer lies in the fact that sleep is not uniform throughout but has stages. Deep sleep is one such stage that is associated with the slowest brain waves during sleep i.e. in this stage the body and the brain waves slow down and therefore make it very hard to wake up. This period of sleep is also known as slow-wave sleep. Experts recommend that adults must get 7 to 9 hours of sleep per night out of which 13-23% is deep sleep (Mayoclinic, 2019).
There are 5 stages of sleep that rotate between non-rapid eye movement (NREM) and rapid eye movement(REM).
- Stage 1: This is the stage wherein you drift from being awake to falling asleep. The time durations for this NREM sleep are short. You start to relax and dream during this stage.
- Stage 2: The individual in this stage is still in light sleep but is proceeding toward a deeper sleep. The heart rate and breathing rate start to slow down and muscles begin to relax. The brain waves become less active.
- Stage 3 and 4: You begin entering deep sleep in stage 3 and you are in your deepest sleep in stage 4. The heart rate, breathing rate, brain waves, and body temperature are at their lowest levels during deep sleep. The muscles are extremely relaxed. Stage 4 is also known as the healing stage wherein the cells are repaired and various important hormones are released for their respective functions. However, there has still not been a clear distinction between the benefits of these two stages and hence they are combined into a single stage called N3.
- REM sleep: The first REM cycle of the night begins about 90 minutes after you fall asleep and recurs every 90 minutes[1]. There are rapid eye movements and the brain waves are similar to an awake person. The breathing, heart rate, and blood pressure are near waking levels. You are most likely to dream at this stage.
Deep sleep is very important for a healthy brain and body:
- Helps to store and create new memories
- It is the state where the brain “rests” and recovers and replenishes the energy spent throughout the day.
- This state of deep sleep is essential to keep the hormones balanced. For example, the human growth hormone is secreted by the pituitary gland which helps tissues to grow and cells to regenerate.
- Blood sugar levels and metabolism balance out
An overall sleep of 7 to 9 hours is a must for most adults as it gives the body enough time in deeper states of sleep. The body tries to compensate for the lost sleep in upcoming days i.e. if the body does not get enough sleep one day then it tries to make up for the same the next day by moving through the cycles quickly to reach deep sleep faster and stay there longer. However, this should not happen regularly as it eventually starts to affect the brain.
What can be done to increase the amount of deep sleep?
- Try to set aside more time for sleep as it allows the body to go through more sleep cycles which enables it to have a deep sleep.
- Expending energy through physical exercises such as jogging, running, or swimming early in the day promotes good sleep.
- Diet changes: Try eating fewer carbohydrates and a healthier diet
- Try to reduce stress
- Establish sleep rituals and routines
- Meditate
- Avoiding bright blue lights such as smartphones and computers near bedtime[2]
Why are short afternoon naps not able to affect nighttime sleep compared to longer ones? It is also because the duration is not sufficient for the body to cycle into deep sleep thus not affecting the sleep drive.
Sleep deprivation adversely affects the body:
- Frequent mood swings
- The problem in retaining things
- Having trouble concentrating
- Blood pressure issues
- Poor response time and an increased risk of accidents
- Low sex drive
- Early aging
While all stages of sleep are important, deep sleep is the most essential one. On average, if you sleep for 8 hours, then you get around 1-2 hours of deep sleep which is healthy.
“Sleep is the best meditation.” -Dalai Lama