Introduction
Sleep is crucial for mental and physical health, and it is essential for the homeostasis
of body functions. Sleep restriction or poor sleep quality are associated with substantial
health consequences, including cardiovascular diseases, diabetes, stroke, hypertension,
obesity, and immune system dysfunction, which may increase the risks of inflammation,
some types of cancer, and even death.[1]
[2] Sleep should not only be considered a vulnerable state that persisted in evolutionary
terms.[3]
[4] Indeed, sleep is an adaptive state that enables the efficient use of finite energy.[3]
[4]
[5]
Despite the diverse philosophical approaches concerning sleep and regardless of any
technical definition, sleep happens in all cultures. Sleep patterns differ in distinct
parts of the world and have changed over the course time, but the fact that sleep
has been present throughout time and across cultures is undisputable. In some cultures,
sleep is a mystical and transcendental condition, described as prophetic or influencing
important decisions. In ancient Greece, philosophers considered dreams to be divine
and wrote manuals for their interpretation.[6] Traditions and environmental conditions can also influence sleep habits and practices.
The social sleep hypothesis explains how the early Homo genus overcame the risks arising from the transition to terrestrial segmented sleep:
the idea is that early humans committed themselves to a kind of social niche. It is
known that the controlled use of fire was also essential to ensure terrestrial sleep,
and it enabled the practice of short periods of flexible, but quality sleep.[7]
[8] Coolidge and Wynn (2016)[9] suggested that when hominids became fully terrestrial, they gained the advantage
of having greater stability than when they slept in trees. Thus, they could achieve
sleep with longer duration and better quality, which would have improved the waking
cognition and survival. However, in the last two centuries, much more pronounced alterations
in sleep have occurred which are not simply explained by evolution.
Sleep in Modern Society
Insufficient sleep is a growing problem in our modern society.[10]
[11] In general, adults need approximately seven to eight hours of sleep per night, but
this is often unfeasible nowadays.[2] Data from the United States[12]
[13] show that up to 40% of the population sleep no more than 7 hours per night, while
30% sleep less than 6 hours per night. Over the last 5 decades, a reduction of approximately
2 hours of sleep per night has been observed, and the proportion of individuals sleeping
less than 6 hours has increased ∼ 6% since 1985.[12] Similar data have been observed in São Paulo, Brazil, where epidemiological surveys[14] report an average total sleep duration of 6.1 hours per night among individuals
aged between 20 and 50 years. Such alterations are largely attributed to sociocultural
changes, the most important of them being the popularization of artificial light and
industrialization.
A major cultural transformation in sleep patterns has occurred with the introduction
and widespread availability of artificial light.[15]
[16] Electric light was only developed a little over 140 years ago, which is a short
period compared with the emergence of H. sapiens and the structure of our circadian system, but enough to restructure the priorities
of society. One can imagine the impact of artificial light on sleep by considering
life before the electric light was invented or widely available. The sources of light
after sunset were basically fire, candles and lamps. As few human activities are performed
in the absence of light, sleep becomes a natural behavior that helps the organism
to recover and the individual pass the time, for it is a period of preconditioned
interruption of most activities. Electric light is a factor that powerfully affects
our circadian rhythm and is often overlooked when it comes to sleep disturbance. Without
it, only a few people would stay awake at night.[17]
Obviously, our sleeping habits have changed drastically since then. Industrialization
has led to major changes in sleep patterns since its introduction in the mid-eighteenth
century, and when the light bulb was invented by Thomas Edison toward the end of the
nineteenth century, life inside and outside the home changed forever. This invention
made nighttime activities easier and safer and turned sleep into an inconvenient necessity
that could be sacrificed in favor of work or engagement in social activities. Thus,
polyphasic sleep became less prevalent and was gradually replaced by late-onset, single
sleep, although some rural populations still had a biphasic sleep pattern (mostly
composed by a larger nocturnal sleep period and a smaller midday siesta). The nineteenth and twentieth centuries were marked by major technological advances,
the introduction of shift work, and a new understanding of the circadian rhythm. These
major changes resulted in a decrease in sleep duration and, as a consequence, an increase
in sleep-related diseases. This period was also marked by the wider availability of
technological distractions and barriers to an adequate healthy sleep, a process that
persists to date.[18]
[19]
Under these circumstances, currently sleep restriction has become a relevant health
issue. A variety of social and environmental factors affect both sleep duration and
quality. Longer working hours and technological entertainment activities act as contemporary
lifestyle stressors and contribute to sleep insufficiency. Chronic reduction in sleep
is frequently associated with the impositions of modern life, such as domestic and
educational responsibilities and pressure from employers arising from a capitalist
perspective. Although it is essential, sleep reduces the amount of time that can be
devoted to other activities, such as work. The world has entered a frenetic functioning
rhythm (24/7) with an increasing amount of time dedicated to work. If one is to fit
leisure time into this routine, even less time is reserved for rest and sleep.[2]
The main question is: how does the reduction in sleep time affect us on an individual
and societal level? As aforementioned, we now understand sleep beyond its purely behavioral
aspects. It is known that electrophysiological activity in the brain during sleep
produces two distinct and easily identifiable stages, namely rapid eye movement (REM)
sleep and non-REM sleep.[20] Physiologically, during sleep, we experience alterations in the cardiovascular and
respiratory systems and oscillations in the production of hormones and neurotransmitters.
Thus, any disease that affects the quality, timing, or duration of sleep and impacts
a person's ability to properly function while awake is understood as a sleep disorder.
Given the importance of sleep for our physical and mental health, scientists around
the world are dedicated to understanding the causes of sleep disorders and finding
treatments for them. The combined effect of reduced sleep time and the emergence of
sleep disorders has been categorically associated with the emergence of several diseases.
Significant changes in hormone levels have been found[21] in individuals exposed to few hours of sleep per day, and they include elevated
levels of cortisol and ghrelin (an appetite-stimulating peptide), which contribute
to a considerable increase in appetite, leading to a higher risk of developing metabolic
disorders, such as diabetes or obesity.[22] In terms of cardiovascular diseases, workers who sleep less than six hours per day
have a four-fold increased risk of stroke.[23] There are also consequences at the level of the immune system, with an increase
in hypo- and hyperactivity of the immune system, simultaneously promoting autoimmune
phenomena with detrimental effects on acquired immunity, resulting in an ineffective
response to immunization and increased susceptibility to infectious diseases.[24] Therefore, studies in this field are crucial for public health, especially as there
is a bidirectional relationship between sleep and illness. Changing sleep patterns
have renewed the focus of research on this issue, and it is now widely agreed that
good sleep is a necessity to maintain a healthy body and mind.
The longer the duration of sleep restriction, the worse the signs and symptoms. Sleepiness
increases as sleep curtailment continues, but it does not always grow in proportion
to the persistence of chronic sleep restriction. Thus, the physiological response
to sleep loss may depend, to some degree, on the form of sleep restriction (acute
or chronic). The control related to sleep pressure (adenosine and the hypothalamic
system) mediates the level of attention impairment depending on the amount of sleep
loss. Sleep restriction exacerbates preexisting mood disorders such as anger, depression,
and anxiety. Sleep restriction leads to mental confusion, temporal and spatial disorientation,
and fatigue. Authors[25] studying physical and verbal aggression, anger, and hostility in a group of young
adult males found that these individuals reported aggression and anger after sleep
restriction. Sleep restriction increases anxiety levels and significantly affects
the restriction of emotional reactivity as it promotes persistent hyperadrenergic
activity during wakefulness, reducing the amount and quality of subsequent nighttime
sleep, creating a vicious circle. Symptoms of posttraumatic stress disorder have been
induced through selective REM sleep restriction in healthy individuals, with increased
autonomic sensitivity to conditioned stimuli that no longer exist.[26]
The effects of the prevalence of sleep disorders on the individual and society have
gradually become more apparent and have been correlated to the emergence of various
diseases. The literature is scarce about the reasons why some individuals cannot sleep,
particularly from an anthropological perspective, considering the potential impact
on sleep of factors, such as social isolation and difficulties in maintaining relationships.
Healthy contact with spouses, friends or relatives contributes to a feeling of safety
and protection in humans, and disruptions in these relationships can lead to increased
feelings of loneliness and vulnerability that reduce sleep quality.[27]
Sleep should not be considered a purely biological event, but also a sociocultural
phenomenon. After all, the way we sleep is a construction of the society in which
we live. An example of this are the changes in the sleep cycle induced by catastrophic
events such as accidents, natural disasters, and pandemics. As a recent instance,
we can consider the coronavirus 2019 (COVID-19) pandemic, which had a range of direct
and indirect effects on many aspects of sleep.[28] Therefore, social isolation, financial worries, and concerns about the consequences
of this disease significantly increased anxiety, depression, stress, and insomnia,
causing a greater reduction in sleep quality.[29]
[30] Moreover, sleep can be affected not only by disruptions in social relationships
as aforementioned, but also by hunger, lack of temperature regulators (heaters, blankets,
fans or air conditioners), stress, and a broad range of other factors.[31]
Evidence suggests that, in addition to basal temperature, climate can influence sleep
patterns: a study by Mattingly et al.[32] reported that in spring and summer, when the days get longer, the time dedicated
to sleep tends to be shorter. This may be a consequence of the milder weather and
the opportunity to enjoy more outdoor activities, increased light, and higher temperatures,
which affect the circadian rhythm. This is reflected in the fact that the sleep structure
of people living in countries with colder climates and longer winters with shorter
days is different from that of those living in the tropics.[32] This opens the possibility to discuss whether global warming and climate change
could affect sleep in a societal and global level.[33]
The relationship between the structure of society and sleep does not operate in one
direction, as poor sleep can have an impact on several areas, including work and interpersonal
interactions, which have wider societal implications. The social impact of sleep cannot
be underestimated. A lack of quality sleep can lead to irritability, decreased cognitive
functioning, and impaired social interactions. Sleep-deprived individuals often find
it challenging to concentrate, communicate effectively, and regulate their emotions,
which can strain personal relationships and hinder social dynamics within communities.
Among the many mechanisms that contribute to poor health, stress is a factor that
is often ignored, as it is a part of life, but excessive stress can have devastating
consequences. The body's ability to return to normalcy, or the so-called “resilience,”
is the key to preventing stress from becoming deleterious. In this respect, sleep
is vital, as good sleep reduces stress and promotes greater emotional resilience.
Recent studies[34]
[35] suggest that sleep contributes to the development of the system of interactions
in the central nervous system that defines who we are and what information we process,
making sleep an important element in our ability to control emotional stress. The
neurobehavioral consequences of sleep restriction are responsible for the increase
in the incidence of human errors in the workplace, traffic accidents, personal conflicts,
and drug abuse.[26]
[36]
Modern humans sleep less than their ancestors and are more likely to experience sleep
restriction. Modern society fosters a lifestyle that disregards biological circadian
rhythms. The prevalence of early-morning work schedules has made commonplace the use
of alarms that interrupt sleep early. The adoption of artificial light, particularly
at night, as well as the use of electronic devices emitting light have interfered
with the endogenous secretion of melatonin, leading to a restriction in total sleep
time.[37] Observational studies[38] have corroborated these suspicions, with populations in the Amazon rainforest without
access to electrical light exhibiting longer daily sleep durations (> 30 minutes)
than their counterparts with electricity in their homes. In addition, beliefs and
cultural and environmental factors play a role in determining sleep schedules in different
regions. In an increasingly technological, globalized, nocturnal, and competitive
world, it is theorized that sleep schedules have become subservient to work productivity.
This hypothesis takes on particular relevance in countries that have experienced technological
growth after World War II, such as South Korea and Japan. South Korea is a highly-competitive
country in terms of academics and work, where sleep time is shortened by economic
circumstances, being inversely correlated with the time spent at work and with salary.[39]
[40]
[41] Therefore, it is not difficult to understand why South Korea is considered the country
with the lowest average daily sleep duration among the member countries of the Organization
for Economic Co-operation and Development (OECD), with only approximately six hours
allocated for sleep.[42] However, these almost century-old trends exhibit mixed patterns in many countries,
with published studies within the same country revealing contrasting conclusions regarding
the possibility of a gradual decrease in total sleep time between 1960 and 2000.[43]
[44] Sleep disorders are increasingly common worldwide; they affect health and well-being,
and have a wide range of consequences, including decreased work productivity and an
increase in accidents, meaning that these rapid changes in sleep patterns and quality
should be of great concern.
Efforts are needed to provide the opportunity and the right environment for people
of all ages to obtain regular restful sleep that contributes to health maintenance
and improved productivity. We need to develop a better understanding of why sleep
restriction is detrimental to our health as well as the neurological and physiological
mechanisms underlying this. It is necessary to consider this problem from a broader
perspective, considering anthropological and societal aspects that have frequently
been ignored. It is important to note that improving the quality of sleep is not an
obstacle to the modernization and functioning of society, nor does it solve the evident
social issues we face, but it can be a relief from one of their consequences. Modern
society faces a significant number of challenges and social problems, and addressing
the issue of sleep quality, although clearly not a universal panacea, could result
in a significant range of benefits regarding physical and mental health, work, relationships,
and overall quality of life. To foster a healthy modern society, it is crucial to
promote optimal sleep and well-being through the establishment of healthy sleep routines,
the management of sleep disorders, and the incorporation of relaxation techniques
into daily life.
