We spend about a quarter to a third of our lives asleep, but just because we are not awake doesn’t mean that time is unproductive.
The physiological changes that occur when we are asleep determine how well we feel and perform when we are awake.
It’s often said that diet, exercise, and sleep are the three foundational pillars to good health and well-being. While many of us understand the importance of eating a healthy, balanced diet and of keeping fit, we are perhaps less familiar with how important sleep is.
We’ve all experienced the effects of too little sleep: what it means for our mood, focus, and concentration, and also how it affects us physically—we have less energy, and feel tired and groggy. However, the importance of sleep and the consequences of being sleep-deprived go beyond this.
Sleep influences all the major systems in our body, and those systems in turn influence our sleep. Insufficient sleep can disrupt bodily functions that affect how we think and behave, and how we think and behave can disrupt our sleep. Therefore problems with sleeping can quickly become a vicious
cycle.
At its simplest, sleep plays an important role in:
- Creating a healthy immune system
- Consolidating learning and memory
- Regulating growth and appetite through the release of certain hormones
- Regulating mood and emotion.
Sufficient sleep is essential to our well-being, both physically and emotionally, so it is not surprising that when we are deprived of it we feel the impact in all areas of our life. There is plenty of evidence that poor-quality or too little sleep can have serious consequences for our physical and mental health
Research on sleep usually measures objective and/or subjective sleep quality, and there is an important distinction between the two:
OBJECTIVE SLEEP QUALITY
is assessed in laboratory conditions to determine the duration, efficiency, minimal broken sleep, and proper cycling through the different stages of n-REM and REM sleep.
SUBJECTIVE SLEEP QUALITY
is our perception of how easily we fall asleep and whether it feels as if we had enough to feel rested throughout the day. Problems with either can be debilitating, but the difference is significant in that, while it may be difficult to significantly improve sleep objectively for physiological reasons, we can change our perception of our sleep and its quality, and thereby our relationship with it. If we don’t feel depleted by our experience, we are much more likely to view it neutrally or even favorably.
This is where practicing mindfulness meditation may be particularly helpful, since with mindfulness we never “tackle” a problem in order to fix it. Instead, as we learn to accept it, our perception of the difficulty changes and it becomes less of a problem for us. However, we must practice mindfulness meditation to allow this to happen—we can’t just tell ourselves to accept something. Acceptance arises from a raft of things coming together.
WHAT HAPPENS WHEN WE SLEEP?
Until the early 20th century, when we became able to measure brain activity with electroencephalogram (EEG) rays, it was believed that during sleep the brain shut down and rested from the activity of the day. However, the reality is very different, and in fact the brain can be more active when we are asleep than when we are awake.
Whether we are awake or asleep depends on activity in specific areas of the brain. The part of the brain that promotes wakefulness also inhibits the part that promotes sleep activity, and vice versa. The shift between the different areas is caused by internal factors such as the circadian rhythm
Whether we are awake or asleep depends on activity in specific areas of the brain. The part of the brain that promotes wakefulness also inhibits the part that promotes sleep activity, and vice versa. The shift between the different areas is caused by internal factors such as the circadian rhythm and the release of hormones, and is usually self-regulating. The drive to sleep increases the longer we are awake, and as we sleep it abates so that it is near zero when we wake.
Sleep, or more officially the Sleep Cycle, is made up of different stages of REM (rapid eye movement) and n-REM (non-rapid eye movement) sleep. Each cycle lasts about 90 minutes and is repeated three to six times each night. However, this cycle may be disrupted by stimulants such as coffee, nicotine, and alcohol, as well as by medical conditions and sleep deprivation.
We usually spend about 75 percent of the night in n-REM and 25 percent in REM sleep. Each of the different stages is as important as the others, and it is believed that the right balance of all the stages is crucial for restful and restorative sleep, which promotes learning, memory, and growth processes such as cell formation and repair, and regulates mood and the ability to concentrate.
The first cycle begins with a period of n-REM.
N-REM
Characterized by a reduction in physiological activity in the body, sleep gradually becomes deeper and the brain waves slow, along with the breath, heart rate, and blood pressure. Although the following are listed as separate stages, they actually merge into one another
N1 (STAGE 1) Typically lasts 1–7 minutes, when we are hovering between being awake and falling asleep. If we are asleep, it is very light. We may experience sudden muscle jerks preceded by a falling sensation.
N2 (STAGE 2) Lasts about 10–25 minutes and signifies the onset of sleep. Eye movement stops, breath and heart rate become more regular, and body temperature drops. We have disengaged from our surroundings. Brain waves become slower, with occasional bursts of rapid activity. Spontaneous periods of muscle tension are interspersed with periods of muscle relaxation.
N3 (STAGE 3) Typically lasts 20–40 minutes and is also called “Slow Wave Sleep” (SWS). This is our deepest and most restorative sleep, and is believed to be associated with bodily recovery, certain types of learning, and changes to the central nervous system. Children experience the greatest amount of N3 sleep, which decreases with age. The longer someone has been awake, the more N3 sleep they get once N3 sleep occurs. It is harder to wake someone in this stage than in any other, since the brain is less responsive to external stimuli. If we are wakened in this stage, we may feel groggy and disoriented for a while.
Breathing becomes much slower, blood pressure drops, and muscles relax. There is decreased muscle activity, but they can still function. Blood supply to muscles increases. Hormones are released, including the growth hormone essential for muscle development. During this period tissue growth and repair occurs, and depleted energy is restored.
The majority of N3 sleep occurs in the first third of the night. N3 sleep typically takes up less time in the second cycle, and often disappears altogether in later cycles.
Then there is often a series of body movements that signal the ascent toward REM, moving through lighter n-REM. Often you “cycle back up” to N2 for 5–10 minutes before moving into the REM state.
REM sleep usually occurs about 90 minutes after falling asleep. It recurs every 90 minutes or so, and lasts longer as the night progresses. There is intense brain activity similar to when we are awake. This is when we are most likely to dream.
During REM sleep, breathing is faster, shallower, and more irregular. The heart rate and blood pressure increase, and the eyes often dart back and forth, causing the eyelids to flicker. Body temperature drops to its lowest point. Although the brain is awake, the body is paralyzed—a safety measure preventing us from acting out our dreams and perhaps causing injury.
It is thought that memories and learning are consolidated during REM sleep, that the body’s brain chemistry is restored to a natural balance, and that mood is regulated.
RELEASE OF HORMONES
Hormones play an important role in regulating our sleepiness or wakefulness. During the various stages of sleep, some hormones are secreted and/or released and others are inhibited or reduced. These often determine how the body functions, for example suppressing appetite. When our sleep is disrupted, therefore, the hormones are unable to function as they should, and that can have a negative impact on our health and well-being. For instance, diabetes is caused by the body’s inability to produce insulin, and insufficient sleep increases the risk of diabetes. However, those who sleep longer than 9 hours also seem to be at a greater risk of diabetes, so, where insulin is concerned, it seems to be the right balance of sleep that may be significant.
