The Optimal Duration for Quality Sleep

Unveiling the Ideal Time for Rest and Revitalization

Sleep fulfills a crucial biological function, most human beings will sleep more than 175 thousand hours during their lifetime. While we sleep, many changes take place in the body such as variation in EEG waves, rapid eye movements (REM) and changes in the electromyographic activity of the neck muscles. The electroencephalogram (EEG), electrooculogram (EOG) and electromyogram (EMG) of the neck are the three psychophysiological pillars used to define the stages of sleep.

Four Stages of Sleep EEG

Stage 1

As the eyes close, alpha waves begin to mark the low-voltage and high-frequency EEG of the active wakefulness.

Stage 2

It increases the voltage gradually and decreases the frequency of the EEG, it is characterized by the presence of the K-complexes and sleep spindles.

Stage 3

Characterized by the occasional presence of delta waves, which are the largest and slowest waves in the EEG.

Stage 4

It is characterized by the predominance of delta waves. When we reach stage 4, we stay like this for a certain time and then regress until we reach stage 1 (incipient), but now accompanied by eye movements and loss of muscle tone. During the rest of the night we will be moving from one stage to another, in cycles of approximately 90 minutes, spending more and more time in incipient stage 1 (paradoxical sleep), and less time in stages 3 and 4 (delta sleep), in addition to moments of wakefulness that we will not remember in the morning. REM sleep is characterized by rapid eye movements and loss of muscle tone in early stage 1, while slow-wave sleep refers to stages 2, 3, and 4.

There are several common beliefs about dreams that have been the subject of empirical tests, such as incorporating external stimuli into a dream, trying to find out if dreams only last an instant, if there is an absence of dreams, and some others related to sleepwalking.

There are also theories that state that dreams are disguised messages, even Freud pointed out that dreams were repressed sexual desires (a claim that was not proven) but that led to the acceptance that dreams represent repressed thoughts. Lucid dreaming is when we are aware of what we are dreaming and can influence the dream.

Circadian and Recovery Theories

Sleep is a critical function for survival, there are two main approaches based on sleep:

1. Recovery theories, which claim that being awake affects homeostasis, and sleep is necessary to restore it; and
2. Circadian theories, which indicate that we need to be inactive at night to conserve energy resources as they are less susceptible to damage in the dark.

Circadian Sleep-Wake Cycles

“Circadian means approximate duration of one day” (Hastings, 1977)

Human beings are active during the day and sleep at night, this is called the sleep-wake cycle and during this time, our body makes changes to adapt to light and dark conditions which is the most important key that the environment provides to regulate our circadian rhythm.

Jet lag occurs when timers speed up or slow down due to flights crossing different time zones, affecting the person’s circadian cycle, in shift work, there are no variations in timers, but workers are forced to adapt to different sleep-wake cycles. These changes lead to fatigue, sleep disturbances, and physical and cognitive impairments (Pinel, 2003).

Effects of Sleep Deprivation

According to recovery theories, sleep deprivation produces physiological and behavioral disturbances that worsen as the deprivation continues, but they affirm that lost sleep can be regained. On the other hand, in the theory of circadian cycles, it is stated that lack of sleep does not produce debilitating effects, and that there will be no or little recovery of lost sleep.

Experiments have been developed to measure performance in the face of sleep deprivation in three categories:

1. Studies of partial deprivation, sleeping less than 5 hours over a 24-hour period.
2. Studies of total deprivation in short periods, not sleeping for 24 to 48 hours.
3. Studies of total deprivation over long periods, not sleeping for more than 48 hours.

Performance was measured in four categories:

1. Physiological function.
2. Mood.
3. Cognitive measures.
4. Motor activity.

Some of the conclusions of these experiments have been illogical, showing that periods of sleep deprivation of up to 72 hours did not affect strength or motor activity, cognitive abilities were almost immune to sleep disturbances, and no relationship was found between the duration of sleep deprivation and performance deficits. The subjects of the experiments presented periods of microsleep when performing passive tasks, where the eyelids are closed for two or three seconds and there is less reception to external stimuli.

Animal experiments such as those on rats in the carousel apparatus showed that sleep deprivation is not as harmless as it appeared to be in human experiments, but the results were inconclusive as to whether the damage in rats was caused by sleep deprivation or by the stress and physical damage of the experiment.

REM sleep deprivation

When REM sleep deprivation occurs, it has been found that the body tends to show a compensatory increase in REM sleep after the period of deprivation. REM sleep is thought to have a special function related to maintaining mental health, motivation, and processing memories, the experiments to measure these effects have been inconclusive, although they are promising. Tricyclic antidepressant drugs have also been studied in terms of REM sleep effects.

In general, lack of sleep produces negative effects, most people have a feeling of general malaise, and impairment in monotonous cognitive tasks.

Increased sleep efficiency

The discomforts presented by lack of sleep disappear if we gradually adjust to the new sleep schedule. People who spend less time in bed fall asleep faster and wake up less during the night, and slow-wave sleep has been found to be more effective, as well as being associated with a decrease in body temperature, making it clear that it has an important recovery function. When sleep is gradually reduced and there is a process of adaptation, sleep becomes more effective.

Drugs That Affect Sleep

Hypnotic drugs such as benzodiazepines are used to treat anxiety, increase sleepiness and reduce the time needed to fall asleep. They should not be used in the long term as they generate body resistance, they cause insomnia when withdrawn, and they are highly addictive.

Antihypnotic drugs such as stimulants and tricyclic antidepressants increase the activity of catecholamines and their treatment creates addiction and loss of appetite, so they must be controlled with very accurate doses and schedules.

Melatonin, synthesized in the pineal gland, plays an important role in sleep stimulation in mammals, although in humans it is not so clear as studies of its effects are recent.

Sleep disorders

1. Insomnia includes sleep onset and maintenance disorders. Some cases are iatrogenic, that is, caused by doctors prescribing sleep medications without taking into account the development of tolerance and increased dosage, which will produce greater insomnia.
2. Sleep apnea occurs when the patient stops breathing several times while sleeping, which causes him to wake up continuously either consciously or unconsciously, generates a feeling of drowsiness, it is caused by obstruction in the airways or atony, also by failures in the central nervous system.
3. Nocturnal myoclonus and restless legs, which generate discomfort in the legs that prevents sleep, it is commonly treated with benzodiazepines, but they are not effective.
4. Hypersomnia occurs in situations such as narcolepsy, where repeated sleep attacks occur during the day, causing the person to fall asleep while eating, in a conversation, or in other activities.

There are disorders related to REM sleep, such as narcolepsy, in which people enter REM sleep directly when they fall asleep, and cataplexy, which is characterized by recurrent losses of muscle tone during wakefulness, such as those that occur in REM sleep, causing falls and lack of movement for a couple of minutes in a conscious manner. Both disorders are treated with tricyclic antidepressants as they suppress REM sleep. Sleep paralysis and hypnagogic hallucinations are also experiences in which REM sleep invades the limits of wakefulness and are common in cases of narcolepsy.

Effects of Reduced Sleep for Prolonged Periods

There are two types of experiments to measure these effects: in the first one, the subject sleeps a few hours every night and; In the second one, the subject takes short naps throughout the 24 hours of the day (polyphasic sleep).

According to the first experiment, it was found that there were no significant effects on performance or mood, but there was a slight deficit in auditory attention; When the reduction was done gradually, the reduction in sleep time was associated with an increase in sleep effectiveness, although the subjects experienced sleepiness throughout the day.

Regarding to the second experiment (polyphasic sleep), under the premise that Leonardo da Vince used to sleep fifteen minutes every four hours, limiting his sleep time to 1.5 hours a day, the subjects who adapted to this type of sleep did not show deficits in the tests, but showed a preference for certain durations of time by refraining from sleeping too little or sleeping too much as it generated sleep inertia (feeling of lightheadedness) when they woke up.

It was concluded that the most seen effect in humans by the reduction of sleep is sleepiness, general malaise, and the existence of microsleeps that prevent concentration in passive activities at certain times of the day. The significance of adequate sleep cannot be overstated. Striking the right balance in sleep is crucial for overall health, cognitive function, and emotional well-being.

There is an important individual variability in sleep needs, but the general consensus underscores the necessity of 7–9 hours for most adults. However, it is imperative to recognize that quality matters as much as quantity. Prioritizing healthy sleep hygiene, adopting a consistent sleep schedule, and understanding one’s unique requirements contribute to a more profound and rejuvenating sleep experience.

Source:

Pinel, J. (2003). Chapter 12. Sleep, Dreams, and Circadian Rhythms. Biopsychology.

Thanks for Reading. Feel free to share your experience about sleep requirements in the comments, I will be happy to read you!