Why fall in love when you can easily fall asleep!? Yes, sleep is very instinctual to human beings. A good night’s sleep will keep you refreshed throughout the day. 

Often it is observed that a person with the right amount of sleep is more productive compared to the one who is sleep-deprived. Sleep is very essential for basic biological functions in your body. 

Infants need more sleep than toddlers, adolescents need more sleep than young adults, pregnant women and women during postpartum need more sleep than the elderly. 

About 60% of the population is either sleep-deprived or lacking sufficient sleep. Children below 5 years are sleep-deprived too owing to multiple reasons. 

Sleep and your circadian rhythm:

Your sleep is regulated by a physiological clock, that is also known as the circadian rhythm. 

The circadian rhythm is dependent on various factors like the hormone melatonin, daylight and darkness, communication between the neurons, and the state of the body (temperature, stress, hunger). 

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To learn more about Circadian rhythm please read this blog.

The different stages of sleep:

There are two major sleep cycles:

• The non-rapid eye movement sleep (NREM)
• Rapid eye movement sleep (REM)

 Sleep cycling is observed between the NREM and the REM stages and there are 4 to 5 sleep cycles observed in one night. Which means, your eight hours of sleep go through four to five cycles juggling between active and passive sleep. 

The NREM stage:

The non-rapid eye movement (NREM) has 4 stages of sleep.

The NREM is the active stage of sleep constituting 70-80% of sleep time, and the REM is the passive or the dream stage constituting 20-25% of your total sleep time. 

• NREM stage 1:

As one begins to sleep, they enter into the first stage of the non-rapid eye movement sleep cycle that lasts for 7 minutes. At this stage, the facial muscles become slightly relaxed. One gets easily disturbed by noises as this is the light sleep stage. 

Any interruption at this stage will reset the sleep cycle starting from stage 1. 

A 20-30 min nap will put you in stage 1 NREM. 

• NREM stage 2:

This stage lasts for 10-25 minutes in the initial cycle and lengthens with each successive cycle over the night. As this stage lengthens, the person moves into a deep sleep state. This deep sleep stage is very crucial for the brain to develop memory and learning in all ages. 

An interrupted NREM stage 2 can lead to daytime drowsiness, poor memory, and delayed learning abilities.  

• NREM stage 3:

This stage is the deepest non-REM sleep and lasts for a couple of minutes before moving towards stage 4. This is the stage when the body repairs and regrows tissues. As people age, they spend less sleep time in the NREM stage 3 and more time in the NREM stage 2. With growing age, the time spent in each sleep stage declines leading to lesser sleep quality in elderly people. 

• NREM stage 4:

NREM Sleep stages 3 and 4 happen subsequently, transitioning into a deeper state of sleep. Stage 4 lasts for 20-40 minutes in the first cycle and constitutes 10%-15% of the total sleep cycle.  Stage 4 is the most active sleep and there is an extremely low chance of arousal. There is a marked resistance to arousal in this stage. There is no muscle tone, and there are no reflexes. 

Any interruption in the sleep cycles will subsequently lengthen that interrupted stage as a compensatory mechanism. This is called rebound. 

Studies have shown that NREM sleep turns off norepinephrine, serotonin, and histamine receptors and allows them to rest and regain sensitivity. When the nerve cells lose their sensitivity, there is poor communication between the neurons which may critically impaired information processing. Hence, NREM sleep is essential for the brain activities.

(The Neuroprotective Aspects of Sleep - PubMed, n.d.)

The REM stage:

The REM stage is also called the dream state. There is rapid eye movement, loss of muscle tone, loss of reflexes, and suppressed cough reflexes. Unlike NREM, there is an increase in the person’s brain activity as the breathing rate, heart rate, and blood pressure. 

This is not a restful stage of sleep. The breathing rate in this sleep stage is more erratic and irregular. Hence this can also be called a passive stage of sleep. 

• The brain is highly active during this stage of sleep but the reflexes are suppressed. 
• Brain activity during the REM stage is similar to brain activity when you are awake. 
• There are increased levels of oxygen in the brain, elevated pulse rate, and blood pressure.
• People are easily awakened during an REM stage. 
• This stage lasts 10 minutes in the first cycle and can extend to 90 minutes as the cycles pass. 

How does sleep disturbance affect your NREM and REM?

Sleep is often disturbed in psychotic conditions. An anxious person sleeps less than a normal person. 

Any interruption in the REM stage will make a normal person fall back to REM sleep, subsequently lengthening the REM time. This is called REM rebound. However, this is absent in cases of people who have psychiatric illnesses. 

All four stages keep cycling between the NREM and the REM stages by adjusting the cycle time according to the person’s age and mental condition. A healthy person has better sleep rebounds than a person who suffers from psychological conditions.

Can alcohol affect your REM stage?

Alcohol has a profound impact on your sleep. It can act like a sedative for the first few hours and when this effect fades, there will often be sleep disruptions and the person might face insomnia. 

Chronic alcoholism brings major sleep issues. This circadian disturbance disrupts the sleep cycles. The REM stage is the most affected in alcoholics. Alcohol brings more sleep disruptions during the REM stage leading to insomnia and sleep disorders. 

(Here’s How Alcohol Affects Your Sleep, n.d.)

Does caffeine affect your NREM sleep?

Many studies are being conducted to observe how caffeine impacts sleep physiology. Caffeine keeps us alert and awake for a longer duration. When caffeine is consumed 3 hours before bedtime, it can delay your sleep for 40 minutes. 

Caffeine in larger doses influences your circadian rhythm, decreases your active NREM sleep stage, and promotes lighter sleep during the REM stage which can hamper you from achieving quality sleep. 

Caffeine in moderate to lower doses during the daytime does not heavily impact your NREM and REM sleep stages. 

(Burke et al., 2015)

Tips to regulate your sleep cycle:

• It is important to maintain a proper sleep schedule. 
• Maintain a sleep-wake time in your daily schedule. This will ensure that you are achieving quality sleep.
• Avoid gadgets and electronics before bedtime as they can deviate your brain from releasing melatonin - the sleep hormone. 
• Practice breathing exercises to calm down your nerves. This will help you relax and avoid cortisol misalignment.
• Regular exercise and timely food intake must be an essential part of your circadian rhythm, as undigested food will disturb the circadian rhythm.
• Children should be encouraged to sleep early and at the same time daily. They should get at least 10 hours of sleep a day. 

Takeaway

Sleep is the finest nutrition for your brain cells and sleep cycles play an important role in delivering you quality sleep.

Poor sleep can damage your metabolism due to the circadian imbalance. Your sleep, your metabolism, and your mind are interrelated. They work together in a vicious cycle. It is essential to maintain 7-8 hours of sleep a day. With better sleep quality, there will be better productivity.

Sleep quality is as important to children as it is to adults. Children need more quality sleep to develop their cognitive abilities and linguistic abilities. Poor sleep quality in children will lead to daytime drowsiness and crankiness. Studies have shown that children with insufficient sleep are more likely to be slow learners and have delayed milestones for their age.

References:

Burke, T. M., Markwald, R. R., McHill, A. W., Chinoy, E. D., Snider, J. A., Bessman, S. C., Jung, C. M., O’Neill, J. S., & Wright, K. P. (2015). Effects of caffeine on the human circadian clock in vivo and in vitro. Science Translational Medicine, 7(305). https://doi.org/10.1126/SCITRANSLMED.AAC5125

Colten, H. R., Altevogt, B. M., & Research, I. of M. (US) C. on S. M. and. (2006). Sleep Physiology. https://www.ncbi.nlm.nih.gov/books/NBK19956/

Here’s How Alcohol Affects Your Sleep. (n.d.). Retrieved May 9, 2024, from https://www.hackensackmeridianhealth.org/en/healthu/2023/06/14/heres-how-alcohol-affects-your-sleep

Patel, A. K., Reddy, V., Shumway, K. R., & Araujo, J. F. (2024). Physiology, Sleep Stages. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK526132/

The Neuroprotective Aspects of Sleep - PubMed. (n.d.). Retrieved May 2, 2024, from https://pubmed.ncbi.nlm.nih.gov/26594659/