Sleep is far more than a simple break from the day; it is a vital biological process essential for health and wellbeing. Professor Matthew Walker, renowned author of Why We Sleep, describes sleep as the foundation upon which health is built. Without it, our physical and mental resilience may deteriorate. In this article we look at the five stages of sleep, their importance, and the profound effects of disrupted rest on the body and mind

The Four Macros of Optimal Sleep
According to Professor Walker’s research, he suggests that optimal sleep relies upon what he calls The Four Macros of Optimal Sleep (QQRT™) 1) Quantity, 2) Quality, 3) Regularity and 4) Timing Quantity: The National Sleep Foundation (NSF) and the Center for Disease Control and Prevention (CDC) currently recommend that adults (age 18-65) should get somewhere between 7-9 hours sleep per night.
Quality: According to the CDC, a lack of quality sleep impairs clear thinking, memory formation learning ability and overall day-to-day functioning. Quality sleep positively influenced blood sugar regulation , mood regulation, athletic performance and improved immune and mental function. Good sleep quality is vital and is characterised by feeling rested after sleeping and not waking up frequently during the night.
Quality sleep can be identified by the following factors: fewer awakenings during the night, less time spent awake after falling asleep, quality of deep NREM sleep, and how restored and refreshed you feel upon waking.
Regularity: It’s recommended that you go to bed and wake at the same time each give or take 0-20 mins on either side which helps to regulate your internal body clock. According to Professor Walker’s research, maintaining a regular sleep schedule has a substantial impact on reducing the risk of mortality.
Timing: Walker believes that it’s important to align with your sleep chronotype and by learning about your own chronotype you can enhance the quality of your sleep.
The Science of Sleep: An Overview
Sleep is an active state during which the body undergoes essential restorative processes. It is broadly categorised into two main types: Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) sleep. Within these categories are five distinct stages, each serving unique and critical functions. Understanding these stages is key to appreciating the complexity and importance of sleep.

The Five Stages of Sleep
Each night, our brains cycle through the five stages of sleep multiple times, each lasting approximately 90 minutes. Here is an in-depth look at each stage:

N1/Stage 1 (NREM)
Duration: 1-7 minutes.
Characteristics: A transition from wakefulness to sleep, this lightest stage involves slowed breathing, a relaxed heartbeat, and reduced muscle activity. It acts as a gateway into deeper sleep.
N2/Stage 2 (NREM)
Duration: 10-25 minutes.
Characteristics: The onset of true sleep, marked by sleep spindles and K-complexes—unique brainwave patterns that shield sleep from external disturbances. Body temperature drops, and heart rate slows further.
N3/Stage 3 (NREM)
Duration: 20-40 minutes during the first sleep cycle, decreasing as the night progresses.
Characteristics: The start of deep sleep, with the brain producing delta waves. This phase is crucial for physical restoration, immune support, and the release of growth hormones.
Stage 4 (NREM)
Duration: Often combined with Stage 3, lasting longer during early cycles.
Characteristics: The deepest sleep stage, vital for physical repair and immune system enhancement. It is the hardest stage from which to awaken.
Stage 5 (REM)
Duration: Initially 10 minutes, increasing with each cycle to reach up to an hour.
Characteristics: Characterised by vivid dreaming, heightened brain activity, and irregular breathing and heart rate. REM sleep is essential for memory consolidation, emotional regulation, and neural repair.
During sleep, we cycle through the five stages approximately every 90 minutes.
In the first half of the night, the body prioritises deep NREM sleep (Stages 3 and 4) for physical restoration.
In the second half, REM periods lengthen, supporting emotional and cognitive processes.
What Happens During Each Stage?
Each stage of sleep plays a unique role in maintaining health:
Stages 1 and 2:
Initiate and stabilise sleep, allowing the body to relax and prepare for deeper stages.
Stages 3 and 4:
Support immune function, repair tissue, and release growth hormones crucial for physical health.
Stage 5 (REM):
Facilitates emotional processing, strengthens memory, and repairs neural connections, underpinning cognitive and mental health.
The Circadian Rhythm: Sleep’s Internal Clock
Our sleep-wake patterns are governed by the circadian rhythm, a 24-hour internal clock regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus. This clock responds to external cues, such as light and darkness, to regulate sleep and wakefulness. Two hormones play an integral part in the regulation of the circadian rhythm:
Melatonin is released into the bloodstream when darkness is detected by the retinas providing a natural signal that it’s time to sleep. Nightime levels of melatonin are around 10 times higher than daytime levels and begin rising approximately 2 hours before bed resulting in increased drowsiness.
Cortisol, released by the adrenal glands, peaks in the early morning as part of the cortisol awakening response (CAR), typically reaching its highest levels 30–45 minutes after waking, usually between 6 a.m. and 8 a.m. Cortisol will then gradually decrease throughout the day with the lowest levels around midnight before it begins to rise again
The Consequences of Poor Sleep
Chronic sleep deprivation has been linked to a range of health issues, including cardiovascular disease, diabetes, obesity, and cognitive decline. Professor Walker’s research highlights the stark reality: insufficient sleep is a silent epidemic with serious consequences for global health.
Sleep is not a passive state but a complex, active process critical to every aspect of health. By understanding the five stages of sleep and the circadian rhythm, we can better appreciate the importance of quality rest. Each stage serves a vital function, and disruptions to this delicate balance can have far-reaching effects on both body and mind. Recognising the role of sleep in our wellbeing is an important step towards valuing and prioritising it in our lives.
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*The advice in this article is for information only and should not replace medical care. As with any nutritional supplement please consult your qualified healthcare professional before use, especially if pregnant, breastfeeding, if you have a known medical condition or are taking medication. Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.