Sleep is a complex biological process that plays a crucial role in our overall well-being. Understanding the different stages of sleep and how they affect our mental and physical health can help us appreciate the importance of getting quality rest every night.
Let’s explore each sleep stage and the potential consequences of missing out on any of them.
What are the Stages in a Sleep Cycle?
A typical sleep cycle consists of five phases: wake stage, three non-rapid eye movement (NREM) stages and one rapid eye movement (REM) stage1. Each cycle lasts about 90-120 minutes, and we usually go through 4-6 cycles per night1.
Wake
A sleep stage is considered wake when it consists of over 50% of alpha wave and eye movement associated with wakefulness. The wake stage is often not considered as a sleep cycle stage.
NREM Stage 1: Light Sleep
This initial stage is a brief transition period between wakefulness and sleep, lasting only a few minutes.
It is the lightest stage of sleep, where you drift in and out of sleep and can easily be awakened. It’s a transition phase from wakefulness to sleep. It consists of 5% of a total sleep cycle1.
Effects of Missing Stage 1
- Difficulty falling asleep
- Reduced overall sleep quality
While the consequences of missing this stage are relatively mild, it can lead to feeling unrefreshed upon waking.
NREM Stage 2: Deeper than Light Sleep
This stage accounts for about 50% of our total sleep time and is characterized by a drop in body temperature and slow heart rate.
It’s a period of deeper sleep before entering the deepest sleep stage, the NREM stage 3.
Effects of Missing Stage 2
- Impaired alertness and attention
- Reduced cognitive functions such as problem solving, quick learning, recognizing people and places
- Decline in ability to control and execute physical movements effectively.
Research has shown that Stage 2 sleep is crucial for memory consolidation and learning2,3. Missing out on this stage can significantly impact your daily cognitive performance.
NREM Stage 3: Deep Sleep or Slow Wave Sleep (SWS)
This is the most healing stage of sleep and the deepest stage of a sleep cycle.
It is harder to wake up from this stage, and it’s when the body repairs tissues and strengthens the immune system1. People will have a short moment of mental fogginess when awoken at this sleep stage.
Effects of Missing Stage 3
- Weakened immune system
- Increased risk of metabolic diseases such as diabetes and obesity
- Impaired physical recovery and muscle growth
- Reduced release of growth hormone which could lead to stunted growth
Studies have shown that disruption of SWS can lead to increased levels of stress hormones, cortisol, and insulin resistance, potentially contributing to metabolic disorders.
REM Sleep: Rapid Eye Movement
This is the stage associated with dreaming, increased brain activity, and temporary muscle inactivity. It starts around 90 minutes of sleep.
This stage is essential for cognitive functions like memory consolidation and emotional regulation.
Effects of Missing REM Sleep
- Mood disturbances and emotional instability
- Cognitive impairment, especially in areas of learning and memory
- Decreased creativity and problem-solving abilities
- Potential exacerbation of mental health issues
Research has shown that REM sleep plays a crucial role in emotional regulation and memory consolidation4. Chronic REM sleep deprivation may be linked to an increased risk of depression and anxiety disorders.
The Cumulative Impacts of Sleep Stage Disruption
While missing out on a single sleep stage for one night may not have severe consequences on your health, chronic interruptions of sleep stages can lead to significant health challenges5, including:
- Cognitive Decline: Consistent lack of quality sleep, especially REM, may lead to cognitive impairment and increased risk of neurodegenerative diseases6.
- Mood Disorders: Disrupted sleep patterns, particularly in REM sleep, may be strongly associated with mood disorders such as depression and bipolar disorder.
- Metabolic Dysfunction: Insufficient SWS has been linked to insulin resistance and an increased risk of type 2 diabetes6.
- Cardiovascular Diseases: Chronic sleep deprivation and fragmented sleep stages can increase the risk of hypertension and heart disease5,6.
- Weakened Immunity: All sleep stages contribute to immune function, and disruption can lead to increased exposure to infections6.
Summary
Each stage of sleep plays a vital role in maintaining our mental and physical health. While occasional interruptions are normal, chronic sleep issues can have significant consequences, including mental health issues. You need to prioritize good sleep hygiene and address any persistent sleep problems with a healthcare professional to ensure that you are getting the restorative sleep your body and mind need. By understanding the importance of each sleep stage, we can better appreciate the value of a good night’s rest and take steps to protect this very important aspect of our health.
References
1. Feriante J, Patel AK, Reddy V, Araujo JF. Physiology, REM Sleep Physiology, Sleep Stages. Published online 2020. https://www.ncbi.nlm.nih.gov/books/NBK526132/
2. SMITH C, MACNEILL C. Impaired motor memory for a pursuit rotor task following Stage 2 sleep loss in college students. J Sleep Res. 1994;3(4):206-213. doi:10.1111/j.1365-2869.1994.tb00133.x
3. Fogel SM, Smith CT. The function of the sleep spindle: A physiological index of intelligence and a mechanism for sleep-dependent memory consolidation. Neurosci Biobehav Rev. 2011;35(5):1154-1165. doi:10.1016/j.neubiorev.2010.12.003
4. Glosemeyer RW, Diekelmann S, Cassel W, et al. Selective suppression of rapid eye movement sleep increases next-day negative affect and amygdala responses to social exclusion. Sci Rep. 2020;10(1). doi:10.1038/s41598-020-74169-8
5. Medic G, Wille M, Hemels MEH. Short- and long-term health consequences of sleep disruption. Nat Sci Sleep. 2017;9:151-161. doi:10.2147/NSS.S134864
6. Teleayo A. The Impact Of Insufficient Sleep On Body Health. Journal of Community Health Provision. 2023;3(2):71-77. doi:10.55885/jchp.v3i2.302
