Beatrice Blanch
Postgraduate Diploma in Medical Technology (PGDipMedTech)
Natural patterns of sleep are something that we are born with, however, their length changes as we progress through life and become older.
Our sleep can be split into
- Non-REM (non rapid eye movement)
- REM (rapid eye movement) sleep
Non rapid eye movement sleep has 3 stages, and we move in and out of these stages during the night. But before we start asking which stage is most important, let’s first see why sleep is vital for our health and wellbeing.
Why is sleep important?
We spend around a third of our lives asleep, which means that important physiological processes occur while we are sleeping. Some of these processes can only occur while we’re asleep, and these include:
- The brain stores new information and creates new connections
- The brain removes waste proteins build-up that accumulates during our waking hours
- Nerve cells communicate and reorganise, which supports healthy brain function
- The body repairs cells, restores energy, and releases molecules like hormones and proteins
That is why after a night of insufficient sleep, many of us have most likely experienced difficulties with learning and memory retention.
A night of poor sleep can impact our decision-making
Also, we can experience mood swings and hallucinations. Those who chronically do not get enough sleep are also at higher risk of
- Alzheimer’s disease
- Parkinson’s disease
- Dementia
- Developing obesity
- Diabetes
- Cardiovascular disease[1]
We now know that having difficulties with sleep are associated with negative effects on well-being, functioning, and quality of life.
A study done in New Zealand in 2001 found that approximately one-quarter of adults in New Zealand may suffer from a chronic sleep problem. This highlights the importance of sleep issues as a major public health issue in New Zealand.[2]
To understand sleep better, we first need to know that it is divided into two states:
- Non-rapid eye movement (NREM)
- Rapid eye movement (REM)
Let’s first start with NREM sleep.
NREM sleep (non-rapid eye movement)
NREM sleep is named so because during this stage eye movements are slow and rolling, rather than rapid. It is made up of 3 stages of sleep, with each stage becoming increasingly deeper sleep.
We typically spend 75-80% of sleep in NREM sleep
The normal adult sleep will begin with NREM stage 1 and cycle through to deeper stages of NREM and REM as sleep progresses.
We cycle through these stages multiple times per night, with one NREM-REM cycle being around 90 minutes long. These states of sleep can be differentiated by their different characteristics.[3]
Important note – Older studies and research on NREM sleep had classified that there are 4 stages of sleep. But in 2007, the American Academy of Sleep Medicine (AASM) combined stage 3 and stage 4 into one stage 3.[4]
NREM Stage 1
NREM stage 1, also called N1, is the stage that the normal adults (excluding individuals with narcolepsy) will enter sleep, and makes up around 2% to 5% of total sleep.[3]
This stage of sleep acts as a transitional stage between wakefulness and sleep, and also helps transition from NREM to REM sleep later on.[5]
NREM stage 1 is the lightest stage of sleep
During this stage, our body is just starting to relax. Our heartbeat and breathing start to slow down, our eye movements become slow and rolling and our muscles begin to relax. If we were woken up while in stage 1 of sleep, we might feel that we were not sleeping at all.
During a polysomnography sleep study, we can see when a person begins to transition into stage 1 because of the change in brain activity. We start to produce low amplitude, mixed frequency waves called theta waves.
A person will then quickly transition into a deeper stage of sleep, which is NREM stage 2, which we covered in more detail below.[4,6]
NREM Stage 2
Stage 2 of NREM sleep lasts between 10 to 25 minutes per cycle, with each cycle during the night generally becoming longer.
We spend around half of our sleep in stage 2 of NREM
Even though stage 2 is still considered one of the lighter stages of sleep, it would take a larger stimulus to wake someone up in comparison to stage 1.[3]
In NREM stage 2 our heart rate and breathing continue to slow down, the body temperature starts to drop and our entire body continues to relax. There is very minimal or no eye movements during this stage.
Stage 2 of NREM is characterised by two brain wave features:
- Sleep spindles
- K-complexes
Sleep spindles are short bursts of activity lasting 0.5 to 3 seconds. They are linked to memory consolidation, and it is thought that they might be important for processing new content learned.[7]
K-complexes are a sharp peak of electrical activity followed by a negative dip. It is thought that these K-complexes help us sleep by suppressing reactions to stimuli while asleep, so that we don’t get woken up by harmless activity. They are also thought to contribute to memory consolidation as well.[8]
NREM Stage 3
NREM stage 3 is also called deep sleep or slow wave sleep (SWS) due to the slow delta waves that are present during this stage.
This is a deep stage of sleep, and being woken up from this stage is a lot more difficult than stage 1 and 2. If we are woken up during this stage, we may feel groggy or disorientated.
Our heart rate and breathing are at their lowest rate and there are no eye movements.
NREM stage 3 is when tissue repair and growth, and cell regeneration occurs.[4]
A study done from Boston University also suggests that slow-wave sleep assists the brain in cleaning out toxins via cerebrospinal fluid.[5,9] While all stages of sleep are important, some scientists will agree that deep sleep is particularly crucial for waking up feeling refreshed and healthy.
As we age, we get less deep sleep. Older adults typically spend more time in lighter stages of sleep, resulting in more fragmented sleep and more sleep complaints.[10]
REM sleep (rapid eye movement)
Rapid eye-movement (REM) sleep is named after the bursts of eye movements seen during this stage of sleep. REM sleep consists of two phases
- Phasic REM
- Tonic REM
Phasic REM has the bursts of rapid eye movements, while the tonic REM doesn’t.
Brain activity increases during this stage and is very similar to brain activity when we are awake. Because of this increased activity we experience dreams during REM.[5]
REM sleep makes up around 20-25% of total sleep
The first cycle of REM sleep will occur around 90 minutes after sleep onset. The first REM will usually take around 10 minutes, and this duration increases every cycle.
The final stage of REM can last between 30 to 60 minutes. During REM, most muscles in our body become atonic, which is a temporary paralysis. The two exceptions to this paralysis are the eye muscles and respiratory muscles. This atonia is thought to minimise us acting out our dreams at night.[4]
The amygdala is the part of our brain which processes emotions, and is active during REM sleep. Memory consolidation also occurs during REM.
REM sleep is involved in the processing of emotions
Because newborn babies spend more time in REM sleep compared to adults (around 50% of sleep), it is hypothesised that REM also plays a role in brain development.[11]
Related Questions
1. Is REM sleep light or deep sleep?
Because our brain activity during REM is very similar to when we are awake, REM sleep is not classified as “deep” sleep.[10]
2. What is the best type of sleep?
Although all stages of sleep are important and necessary, slow wave sleep (NREM Stage 3) is very important for feeling physically rested, while REM is important for brain recovery.[12]
3. What is sleep latency?
Sleep latency, or sleep onset latency, is the time it takes for us to fall asleep. Normal sleep latency should be between 10 and 20 minutes.[13]
4. What causes fragmented sleep?
Increased sleep fragmentation can occur due to different reasons, such as
- Ageing
- Sleep disorders (obstructive sleep apnea and restless leg syndrome)
RELATED — Sleep apnea: How to cure it and get your sleep back
Stress, anxiety, and other medical conditions or medications can also cause interrupted sleep. Some lifestyle choices such as alcohol or caffeine consumption, or too much light before bedtime can also interfere with sleep.[14]
Also, eating right before going to sleep is not recommended.
RELATED — Intermittent Fasting: The Medicine of Old
5. Does magnesium help with sleep?
Magnesium may help regulate neurotransmitters that are directly related to sleep. However studies on the effect of magnesium involve relatively small cohorts, they have been found to improve subjective measures of sleep.
If you do decide to take magnesium supplements, you shouldn’t take more than the recommended amount and make sure they don’t interfere with any other medications you take.[15]
RELATED — Magnesium (for a great night of sleep)
Let us know in the comments if you liked the article, and also – have you tried different apps and gadgets to measure and quantify your sleep quality?
Beatrice is currently completing her Postgraduate Diploma in Medical Technology, with an endorsement in Sleep Medicine, and has been fortunate to be working in healthcare in conjunction with her postgraduate studies.
Since starting, Beatrice has seen first-hand the effects of lifestyle on sleep hygiene, and the relationship between poor sleep and preventable chronic diseases. Beatrice aims to use scientific evidence-based research to help educate people on the importance of healthy sleep hygiene so that they may improve the quality of their life.
References
(1) Patel AK, Reddy V, Araujo AF (2022). Physiology, Sleep Stages. StatPearls. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK526132/
(2) Paine SJ, Gander PH, Harris RB, Reid P (2005). Prevalence and consequences of insomnia in New Zealand: disparities between Maori and non-Maori. Aust N Z J Public Health 29, 22-28.
(3) Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten HR, Altevogt BM, editors (2006). Sleep Physiology. Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem. National Academies Press. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK19956/#:~:text=NREM%20sleep%20constitutes%20about%2075,Carskadon%20and%20Dement%2C%202005
(4) Healthline (2021). Everything to Know About the Stages of Sleep. Retrieved from https://www.healthline.com/health/healthy-sleep/stages-of-sleep#stages-of-sleep
(5) Jacobson K (2020). Stages of Sleep: NREM Sleep vs REM Sleep. American Association of Sleep Technologists (AAST). https://www.aastweb.org/blog/stages-of-sleep-nrem-deep-sleep-vs-rem-sleep
(6) Suni E (2022). Stages of Sleep. Sleep Foundation. https://www.sleepfoundation.org/stages-of-sleep
(7) Schonauer M (2018). Sleep Spindles: Timed for Memory Consolidation. Current Biology 28, R656–R677. Retrieved from https://www.cell.com/current-biology/pdf/S0960-9822(18)30375-0.pdf
(8) Pacheco D (2022). What is NREM Sleep?. Sleep Foundation. https://www.sleepfoundation.org/stages-of-sleep/nrem-sleep
(9) Makin S (2019). Deep Sleep Gives Your Brain a Deep Clean. Scientific American. https://www.scientificamerican.com/article/deep-sleep-gives-your-brain-a-deep-clean1/
(10) Cleveland Clinic (2020). Sleep Basics. https://my.clevelandclinic.org/health/articles/12148-sleep-basics
(11) Summer J (2022). What is REM Sleep and How Much Do You Need? Sleep Foundation. Retrieved from https://www.sleepfoundation.org/stages-of-sleep/rem-sleep#:~:text=Why%20Is%20REM%20Sleep%20Important,processing%2C%20and%20healthy%20brain%20development.
(12) Price M (2020). REM vs. deep sleep: How your sleep cycle works. CNET. Retrieved from https://www.cnet.com/health/sleep/how-sleep-cycles-work-rem-vs-deep-sleep/
(13) Pacheco M (2022). Sleep Latency. Sleep Foundation. Retrieved from https://www.sleepfoundation.org/how-sleep-works/sleep-latency
(14) Suni E (2022). Interrupted Sleep. Sleep Foundation. Retrieved from https://www.sleepfoundation.org/sleep-deprivation/interrupted-sleep
(15) Abbasi B, Kimiagar M, Sadeghniiat K, Shirazi MM, Hedayati M, Rashidkhani B (2012). The effect of magnesium supplementation on primary insomnia in elderly: A double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences 12, 1161-1169. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3703169/
