How well we sleep—in terms of both duration and quality—plays a vital role in how well our brain and body functions. Sleep enables the brain to clear out toxins that build up during the day; reset hormone and other neurochemical levels; consolidate memories important for learning and other cognitive functions; and protect against illness and disease. Sleep is also paramount for maintaining stable moods and emotional regulation.
At a cellular level, all of these physiological activities enable the brain and body to maintain overall homeostasis. In this way, sleep is a regulatory process. But to truly appreciate how to maximize sleep quality so that you give your brain and body enough time to rest, reset, and restore, you also have to keep in mind that sleep is complicated.
Sleep Basics
Sleep involves two underlying biological processes: our sleep drive, the physical need for sleep that’s as strong and necessary as the drive to eat; and our inner clock that cues us to go to sleep, which we refer to as the circadian clock.
These two distinct but interrelated processes work in tandem so that we go to sleep, stay asleep, and wake up feeling refreshed. However, a lot of people experience difficulty in one or more ways: they have trouble falling asleep, have trouble staying asleep, dream excessively, or move during their sleep. Any one of these can disrupt sleep quality, which in turn affects how well the brain and body reset during the night.
Throughout a night, we cycle through four stages or states of sleep, with each stage presenting its own brain wave (as measured by an EEG) that reflects how much or how little brain activity is happening within that stage:
- Stage N1 (NREM stage 1)
- Lightest stage of sleep, lasting from one to seven minutes
- Comprises about 5% of total sleep time
- Easy to wake someone up
- Characterized by slow eye movements and relaxed muscles
- Brain waves transition from wakefulness to sleep patterns
- Stage N2 (NREM stage 2)
- Deeper sleep, lasting 10 to 25 minutes in the first cycle
- Makes up about 45% of total sleep time
- Body temperature drops, muscles relax further
- Breathing and heart rate slow down
- Brain waves show sleep spindles and K-complexes
- Bruxism (teeth grinding) may occur
- Stage N3 (NREM stage 3)
- Deepest non-REM sleep, lasting 20 to 40 minutes
- Comprises about 25% of total sleep time
- Difficult to wake someone up
- Characterized by slow brain waves (delta waves)
- Important for physical restoration, tissue repair, and immune system strengthening
- REM sleep
- Final stage of the sleep cycle, lasting 10 to 60 minutes
- Makes up about 25% of total sleep time
- Rapid eye movements occurring behind closed eyelids
- Brain activity similar to wakefulness
- Muscles paralyzed (except for occasional twitches)
- Dreaming typical during this stage
- Important for cognitive functions and memory consolidation
A complete sleep cycle lasts approximately 90 to 110 minutes, and people typically go through four or five cycles per night. What’s important to understand is that disruptions in sleep are related to, but are different from, another important dimension to sleep: circadian clock disruption.
Sleep Stages
In general, sleep is either light or deep and is either REM or non-REM, the latter which refers to whether sleep includes dreams or not We cycle through four stages or states of sleep, with each stage presenting its own brain wave (as measured by an EEG) that reflects how much or how little brain activity is happening within that stage.
Stage 1, which is relatively short, occurs when you first fall asleep; your heartbeat and breathing slow down and your muscles relax. Stage 2 is the longest part of the sleep cycle; it’s characterized by light sleep, a drop in body temperature, cessation of eye movements, and a slowing down of brain wave activity. Stage 3 is a period of deep sleep and happens in the first half of the night; this is the type of sleep that’s most acutely tied to the feeling we have of waking up refreshed.
Both stage 3 and stage 4 sleep (also known as slow-wave sleep or SWS) are important for physical and mental health, and they serve different functions. During stage 3 sleep, the body undergoes physical restoration and repair, such as muscle growth and tissue repair. This stage is also important for strengthening the immune system, which helps protect the body against infections and diseases. During stage 4 sleep, the brain processes and consolidates memories, which is important for learning and retaining information. It is also during this stage that the brain flushes out metabolic waste products that build up during waking hours, which may help prevent neurological disorders; this process is known as glymphatic drainage.
Overall, both stage 3 and stage 4 sleep are important for maintaining optimal health and well-being, and it is essential to get enough of both stages of sleep for overall health. The ideal proportion of stage 3 and stage 4 sleep varies from person to person and can change throughout the lifespan, but a healthy adult typically spends about 20% to 25% of their sleep time in SWS (combining stages 3 and 4) and about 20% to 25% of their sleep time in REM sleep. In REM sleep, the brain is most active (i.e., dreaming). Interestingly, during this period, your heart rate and blood pressure resemble your typical daytime levels.
Sleep Is Essential and Serves Multiple Purposes
Most researchers agree that sleep regulation does not have one particular physiological purpose, but rather is essential for many purposes, including the following:
- Development
- Energy conservation/brain waste clearing
- Modulation of immune response
- Cognition
- Performance
- Vigilance
- Disease
- Psychological states
As I’ve often discussed, sleep plays a critical role in maintaining redox balance by increasing the production of nicotinamide adenine dinucleotide phosphate (NADPH), which is an important reducing agent that helps neutralize oxidants and maintain redox balance.
Research has shown that NADPH production is highest during the night, when we are asleep. This is because the enzymes involved in NADPH production are regulated by the circadian clock, which controls many physiological processes in the body, including sleep–wake cycles.
During sleep, the body’s metabolic rate decreases, and energy is redirected toward repairing and rejuvenating processes. This allows for an increase in NADPH production, which helps to counteract the effects of oxidative stress that can accumulate during the day.
NADPH is also important for other processes in the body, such as the synthesis of fatty acids and the regeneration of antioxidants such as glutathione (GSH). By increasing NADPH production at night, sleep helps to maintain a healthy redox balance, which is important for general health and well-being.
Overall, the relationship between sleep and redox is complex, and there are many factors that influence this balance. However, it is clear that sleep plays a critical role in maintaining redox balance, and by increasing NADPH production at night, sleep helps to counteract the effects of oxidative stress and promotes optimal health.
Read Part 2 Now
In the next article, we pick up where we left off starting with the significance of circadian clock disruption and exploring the impacts of GLP-1s and other peptides on sleep. Click here to read Part 2 now.