The Science of Sleep Quality: The Three Rs of Sleep

 

Sleep quality isn’t just about getting lots of deep sleep. Explore the three Rs and how light, deep and REM sleep work together as part of the sleep journey. Simple steps to improve sleep naturally.

In recent years, Sleep has become a hot topic and the subject of health news and internet bio-hackers who are trying to monitor and perfect sleep-related behaviours and metrics. But before we jump headlong into the topic and try to improve things, it helps to understand what “good sleep” actually means physiologically speaking.

Sleep is not a single unconscious state. It is an active, changing, cyclical process made up of distinct neurological stages that ebb and flow throughout the night. Each sleep stage contributes towards the restoration and renewal of the body and how we will feel when we wake in the morning. A little grogginess (sleep inertia) is normal in the first few minutes after waking, but within 10-15 minutes (and without caffeine), ideally, we should feel pretty alert, refreshed and energised for the day ahead. If that is not your experience, then chances are something is not quite optimal with your sleep. 

So often, the blogs, videos, and articles on the subject hail the value of achieving high quality sleep - often, incorrectly framed as maximising deep sleep only. This is only partially true. Quality sleep is not about maximising just one stage. It is about facilitating the whole process of sleep to obtain a better holistic outcome.

Sleep Architecture: Cycling at Night

Across a typical 7–9 hour night, we move through 4–6 sleep cycles. Each sleep cycle takes between 70-120 minutes, with cycles typically lasting longer earlier in the sleep period and gradually becoming shorter as the morning approaches. The phases or stages of sleep have been scientifically categorised according to how brain wave patterns appear when they are being monitored by a polysomnography (literally means 'many sleep writings') machine. 

The nightly journey through the different sleep stages follows a predictable pattern in healthy individuals: Light > Transition > Deep > Transition > REM. The pattern repeats several times during the night. As the night progresses, the duration of the deep, delta wave sleep becomes shorter within a cycle and the Transitional/REM periods of theta and random wave sleep become longer¹.

The ebb and flow of brain wave patterns in and out of neurological cycles is a normal and desirable part of healthy sleep processes. These sleep stages provide the three fundamental 'Rs' of sleep; the Ramp in and out of deep sleep, the Road to Restoration of the body, and the Recalibration of the brain. All three stages form a necessary part of the sleep journey to reach our destination...a refreshed and rejuvenated self the next morning. 

Light Sleep: On and Off Ramp

Light sleep, particularly stage transitional sleep, makes up the largest proportion, accounting for approximately 45–55% of total sleep in healthy adults².

Too often light/transitional sleep is dismissed or undervalued as not being restorative, but that tends to overlook its purpose in the wider function of sleep architecture. During this stage:

• Brain activity slows as consciousness fades, the brain disengages from external stimuli, and relaxation sets in.

• Provides a vital passage of transformation, the on-ramp from wakefulness into deep sleep. 

• Provides the reverse passage of transformation, the off-ramp from deep sleep into REM sleep. 

• Theta wave sleep helps to evaluate new information from the day, determining whether memories should be organised and consolidated, or released and forgotten.

• Theta state sleep is associated with processing emotions and helping the brain to manage emotional build up and stress, reducing anxiety and worry.

• This phase of sleep enables the brain to make unusual, creative connections.

Light/transitional sleep acts as a vital on-ramp from wakefulness into deep sleep, and then again as the off-ramp from deep sleep into REM state sleep. It supports cognitive processing, memory, learning, and emotional integration³. Without sufficient light stage sleep, the overall sleep experience becomes unstable and fragmented, often negatively affecting the amount of deep sleep obtained.

Deep Sleep: Road to Restoration

Deep sleep, often called slow-wave delta sleep, typically accounts for 15–25% of total sleep time in healthy younger adults². The proportion of deep sleep we experience typically declines with age⁴.

This stage is characterised by slow, high-amplitude delta brain waves, muscle relaxation with virtually no body movements, and a reduction in heart rate and blood pressure. The purpose and functions of deep sleep include:

• A large spike in growth hormone secretion.

• Enhanced cellular and tissue regeneration and repair.

• Slows metabolism by approximately 15%, enabling better recovery and hormone regulation, while also improving insulin sensitivity and blood glucose management.

• Brain detoxification and flushing out metabolic byproducts from the day. 

• Upregulation of immune function and immune cell distribution. 

• Solidifying of factual, long-term knowledge and memories.

Deep sleep, therefore, greatly facilitates physical restoration of the body, metabolic regulation, and recovery from the physical strains of the day⁵. Travelling the road to restoration several times during the night is very important to sleep quality, but it is not the only indicator for obtaining a good night's sleep.

REM Sleep: Recalibration

Rapid Eye Movement or REM stage sleep typically accounts for 20–25% of total sleep time in healthy adults², with the duration of REM typically becoming longer in the sleep cycles that occur in the latter part of the night. REM sleep is a critical phase of the sleep cycle often referred to as 'dream sleep' or 'paradoxical sleep' due to a combination of high brain activity and temporary muscle paralysis (which helps to us prevent acting out vivid dreams).

During this random brain wave sleep:

• Short-term memory is consolidated into long-term memory. 

• Strengthens neural connections, improves problem solving capacity, and enhances mental processes related to learning new tasks. 

• Supports ongoing neural development, brain plasticity, recalibration and repair. 

• Regulates emotional intensity, allowing for better emotional stability, mood regulation, and reduced reactivity the next day.

One way to view REM sleep is like biological maintenance garage that provides us with daily servicing that recalibrates the brain⁶.

If sleep is cut short of its requirements, only 6 hours instead of 7-9 hours, then this disproportionately reduces REM sleep, which is more prevalent in the latter half of the sleep period. A lack of REM sleep, just like a missed car servicing, allows for greater wear and tear to occur, impacting memory, concentration, and creativity, while elevating stress and the tendency to be more reactive to minor problems. This is a major reason why sufficient, consistent sleep duration matters!

What Makes a Good Night's Sleep?

If we consider the average healthy adult obtaining the recommended 7–9 hours of sleep per night, the typical distribution of sleep stages will look approximately like this²:

• Light / Transitional sleep (Ramp): 45–55%
• Deep sleep (Restoration): 15–25%
• REM sleep (Recalibration): 20–25%

Seen through the lens of the 3 R’s, a good night’s sleep is not dominated by only one stage, it is a cyclical, harmonious journey that requires all three elements to play their part along the way.

Light or transitional sleep forms the on and off Ramp. It makes up the largest portion of the night because it is the connecting link between the other sleep stages. It gradually merges us into deep sleep and later guides us away towards REM sleep. 

Deep sleep is the primary road to Restoration. This is where the body repairs cellular tissue, supports immune function, and resets metabolic processes. It is the main event, but it is not required to occupy the entire duration of the night.

REM sleep facilitates important Recalibration. This is where emotional tone, memory processing, and cognitive clarity are refined. As the night progresses, REM periods lengthen, preparing the brain for the psychological demands of the coming day.

There will always be natural variation. Physical exertion, illness, stress, emotional load, and accumulated sleep debt can all temporarily shift sleep stage proportions. After intense physical activity, you may observe more Restorative deep sleep. After heavy cognitive or emotional demand, you may see extended REM and Recalibration. Sleep inherently adapts to the demands of life.

One night of recorded sleep data is not a final verdict regarding the type of sleeper you are. It is only a brief a snapshot of how sleep was for that single night.

The key principle is this: sleep quality is not about chasing ever-greater amounts of deep sleep (unless it is clinically deficient). It is about protecting the cyclical harmony of the three stages of sleep; Ramp, Restoration, and Recalibration.

When the sleep journey flows smoothly between these three phases, repeatedly, across the night, then sleep tends to feel whole. Refreshing, whole sleep is what ultimately restores both body and mind.

A Word on Sleep Trackers

Wearable sleep trackers, such as watches and rings, are increasingly common. They offer a digital means of gathering useful sleep data that can help identify patterns such as consistency of schedule or total sleep duration.

However, independent validation studies comparing commercial devices to laboratory polysomnography (the gold standard) show mixed results. Most modern wearables demonstrate a satisfactory level of sensitivity for detecting sleep versus wake, which means they can measure sleep duration just fine. However, as things currently stand at the time of publishing, their ability to accurately classify specific sleep stages, such as distinguishing deep sleep from REM, remains quite limited⁷⁸. This is because sleep staging is really a measure of brain wave patterns. Trackers worn on the wrist or hand typically measure movement and heart rate, factors that have an association with sleep staging, but of themselves are not perfectly aligned with different sleep stages. 

In other words, they provide an indication, but they do not measure precisely. I am not discouraging the use of digital sleep trackers, but the importance and value we attach to the data needs to be managed appropriately. 

Another important consideration is that for some individuals, excessive focus on nightly sleep tracker scores can increase anxiety around sleep, a phenomenon known as orthosomnia⁹. Ironically, worrying too much about achieving 'perfect sleep' can increase stress and have a negative effect that makes sleep worse. 

Facilitating not Controlling Sleep

Sleep is a natural physiological process. It cannot be forced, but it can be gradually facilitated. We can nudge ourselves a little at a time in the direction of falling asleep, but at some point each night we simply need to abandon control and allow ourselves to ease into the natural process of sleep. 

Evidence-supported sleep behaviours that are considered good practice and that nudge us towards better sleep are:

• Consistent sleep and wake timing (stabilises circadian rhythms¹⁰)
  Going to bed and waking up at broadly similar times helps anchor the internal biological clock. This does not need to be strict 'to the minute' scheduling, but large weekday or weekend shifts in sleep timing can significantly disrupt circadian rhythms associated with sleep. Think rhythm and regularity, not perfection.

• Morning light exposure (anchors biological clocks¹¹)
  Receiving a few minutes of natural daylight within the first hour of waking signals to the brain that the day has begun. This is like pressing the start button on a timer delay that oversees future, carefully timed melatonin release that will occur later that evening. 

• Daytime physical activity (improves slow-wave sleep and efficiency¹²)
  Physical movement, whether simple physical activity or structured exercise, helps to expend energy and build sleep pressure that is needed to fall asleep. Movement does not need to be intense, but the body does tend to respond well to regularity.

• Curbing caffeine (potent sleep disruptor)
  Caffeine consumption typically reduces sleep duration by approximately 45 minutes¹⁴, reducing deep sleep and increasing light/transitional sleep. Caffeine timing matters more than absolute elimination, with evidence suggesting last caffeine consumption of the day should be 9 hours prior to bedtime to reduce the risk of a negative effect upon sleep.

• Managing chronic stress (reduces fragmentation and REM disruption¹³)
  Gentle regulation practices, such as slow breathing, light stretching, and journaling, can all help the nervous system shift from a state of vigilance to one of relaxation and recovery. Small daily signals that can quickly become associated with a bedtime routine and sleep.

These positive behaviours do not command sleep, but they do reduce surrounding friction and noise, enhancing the likelihood of good sleep occurring.

Reframing sleep

Sleep quality is not something to chase or control. It is something to facilitate and protect.

When we stop trying to control every aspect of sleep and instead focus on supporting it, nudging it in the right direction, something often shifts in our favour.

Sleep becomes less of an effort, it becomes refreshing and restorative. 

References:

1. Carskadon MA, Dement WC. Normal human sleep architecture. Principles and Practice of Sleep Medicine. 2011.
2. Ohayon MM et al. Meta-analysis of sleep parameters across lifespan. Sleep. 2004.
3. Rasch B, Born J. Sleep’s role in memory consolidation. Physiol Rev. 2013.
4. Mander BA et al. Sleep and aging. Neuron. 2017.
5. Xie L et al. Sleep drives metabolite clearance from the brain. Science. 2013.
6. Walker MP, van der Helm E. REM sleep and emotional regulation. Curr Biol. 2009.
7. Chinoy ED et al. Performance of wearable sleep trackers. Sleep. 2021.
8. de Zambotti M et al. Wearable sleep technology validation review. Sleep Med Rev. 2019.
9. Baron KG et al. Orthosomnia: Quantified self: Sleep tracking and insomnia. J Clin Sleep Med. 2017.
10. Stothard ER et al. Circadian entrainment and performance. Current Biology. 2017.
11. Czeisler CA et al. Light and circadian regulation. Science. 1999.
12. Kredlow MA et al. The effects of physical activity on sleep: a meta-analytic review. J Behav Med. 2015.
13. Meerlo P et al. Effects on autonomic function, neuroendocrine stress systems and stress responsivity. Sleep Med Rev. 2008.
14. Gardiner C et al. The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Med Rev. 2023