Definition of sleep
Sleep is a behavioral state with well-defined physiological characteristics. Similar to hibernation, tonic immobility, coma or general anesthesia, sleep is the only state that simultaneously presents reduced responsiveness, rapid reversibility and is homeostatically regulated (Anafi, Kayser, & Raizen, 2019). During sleep, the living being is physically vulnerable, considering the low capacity to respond to environmental stimuli, in addition, during sleep the living being does not eat, drink or reproduce.
Sleep Function Theories
Even with negative survival factors associated with sleep (greater vulnerability), physiological events occur during sleep that contribute to the proper functioning of the body. Cognitive function hypotheses (e.g., learning, memory and synaptic plasticity) are proposed (See: https://www.condorinst.com.br/cognicao-e-sono-as-influencias-que-um-sono-ruim-tem -na-cognicao/) and hypotheses of restorative functions (e.g., maintenance of brain energy metabolism, macromolecular biosynthesis and removal of metabolic waste) (Frank & Heller, 2019). Despite being extensively studied with more than 200 thousand articles indexed in PubMed with the term “Sleep”, in more than 200 years of research, sleep still remains a scientific enigma. Some questions remain unanswered: Why do sleep properties change throughout life? Why and how is sleep homeostatically regulated? Why should the brain be “turned off” to perform the proposed functions? And why are there two different stages of sleep? (Frank & Heller, 2019). Considered the last major physiological process still without consensus as to its function, some sleep functions have been discussed/speculated in the literature I) immune function (see: https://www.condorinst.com.br/sono-e-imunidade- 2/), II) restorative function of brain energy stores, III) glyphic function, IV) restorative function of performance due to activity-induced degradation during wakefulness (see: https://www.condorinst.com.br/fadiga -e-sleep/), V) connective function or neural plasticity VI) energy conservation function by reducing caloric expenditure (Krueger, Frank, Wisor, & Roy, 2016).
Sleep is regulated by the influence of two distinct mechanisms. The homeostatic process (S) and the circadian process (C). The S process is characterized by a propensity to sleep, caused by the accumulation of adenosine in the basal forebrain, resulting from the breakdown of ATP during the wakeful state. This process results in drowsiness and the need for sleep with the passage of time awake (homeostatic pressure for sleep) (Borbély, Daan, Wirz-Justice, & Deboer, 2016). Process C refers to biological activities that take place in periods of approximately 24 hours (see: https://www.condorinst.com.br/as-consequencias-dos-disturbios-de-ritmo-circadian-2/) and makes it possible to the human organism an anticipation and preparation for an activity or moment of the day. Our rhythms are synchronized through temporal cues known as “zeitgebers” (from the German Zeit = time, Gebers = donor — biological synchronizer), which provide information about the time of day. It is important to highlight that circadian rhythms are not governed by the environment and have a self-sustained nature and even in the absence of temporal clues (free course) our organism continues to present circadian rhythmicity (Mello, Bittencourt, Pires, Silva, & Tufik, 2008).
Night sleep deprivation
The demands (social or professional) associated with the possibility of activity at night (work or leisure) cause our routine to be dragged into periods when we could/should be sleeping. High levels of circadian misalignment occur in individuals who are forcibly forced to change their sleep and wake rhythms and who remain awake at night as shift workers or electronic-sport practitioners (e-sport — people who compete in digital games) (Gomes, Narciso, de Mello, & Esteves, 2021). This biological rhythm inversion behavior with wakefulness in the dark phase and sleep in the light phase of the day can present health risks (Moreno et al., 2019), whose effects include negative impacts on the metabolic response (Zimberg, Fernandes Junior, Crispim, Tufik, & de Mello, 2012). Thus, we can highlight that sleep in its quantity, quality and ideal moment (night), plays an essential role in health, both in its physical and cognitive aspects.
Effect of sleep on body composition
The biological rhythm changes when we stay awake at night and sleep during the day, impacting significant changes in the body. The body “understands” that it needs to save energy for a longer period of wakefulness and, as adaptation occurs, there is a reduction in basal metabolism that favors the accumulation of body fat. Other losses associated with sleep restriction can be observed by the increase in the levels of ghrelin hormone concentration, as well as the reduction of leptin, responsible for the control of appetite and satiety (Taheri, Lin, Austin, Young, & Mignot, 2004). In this way, the body stimulates an increase in food intake, which can result in an increase in body mass. Muscle atrophy and reduced muscle recovery capacity are also associated with nocturnal sleep restriction and deprivation. It has been hypothesized that muscle atrophy caused by sleep loss is associated with a reduction in anabolic hormones and an increase in catabolic hormones (Dattilo et al., 2011). In general, when you do not have adequate sleep, tiredness, drowsiness and fatigue are evident factors that reduce physical performance, reducing levels of physical activity and performance in daily life actions that can even favor sedentary lifestyle ( Mollicone, Van Dongen, Rogers, Banks, & Dinges, 2010). Considering the above, people who invert their sleep and wake rhythm — such as rotating shift workers and e-sports practitioners — suffer the damage caused by night sleep deprivation and desynchronization of the wake/sleep rhythm. Such damage may include changes in hormone production that favor increased caloric intake, energy accumulation and reduced physical activity that affect body composition. Changing the biological rhythm provides a greater chance of increasing the BMI, due to changes in eating habits, daily routine and energy metabolism. An epidemiological study identified that people who stay awake at night and sleep during the day are 1.5 times more likely to be overweight than those who sleep at night (Hulsegge, van Mechelen, Paagman, Proper, & Anema, 2020). Nocturnal sleep deprivation showed significant associations with the increase in BMI proportional to the hours of sleep lost. An increase of 0.43 kg / m2 was observed every 10,000 hours awake during the night (Peplonska, Bukowska, & Sobala, 2015). Chances were 3.9 higher when there is night sleep restriction for eight or more days a month. Apparently, behaviors considered healthy, such as physical activity, sleep quality and eating habits, are not enough to moderate the correlation between shift work and overweight, while years of exposure to shift work can be a moderating factor (Hulsegge et al., 2020). Thus, healthy lifestyle behaviors alone may not be sufficient to “protect” us against the negative effects of nighttime sleep deprivation on excess weight. On the other hand, obesity is multifaceted and can be influenced by social determinants, income, educational level, health knowledge and social support (McGlynn et al., 2015).
A atrofia muscular e a redução na capacidade de recuperação muscular também estão associadas a restrição e privação de sono noturno. Foi formulada uma hipótese de que a atrofia muscular causada pela perda de sono está associada a redução de hormônios anabólicos e aumento de hormônios catabólicos (Dattilo et al., 2011). De forma geral, quando não se tem um sono adequado, o cansaço, a sonolência e a fadiga são fatores evidentes que reduzem o desempenho físico, reduzindo os níveis de atividade física e o desempenho nas ações da vida diária que podem favorecer inclusive ao sedentarismo (Mollicone, Van Dongen, Rogers, Banks, & Dinges, 2010). Considerando o exposto, pessoas que invertem seu ritmo de sono e vigília como trabalhadores de turnos noturno e rotativo, praticantes de e-sports sofrem os prejuízos causados pela privação de sono noturno e dessincronização do ritmo vigília/sono, com mudanças na produção hormonal que favorecem o aumento da ingestão calórica, acúmulo de energia e redução da atividade física que prejudicam a composição corporal.
A mudança do ritmo biológico proporciona maior chance de aumento do IMC, devido a mudanças nos hábitos alimentares, rotina diária e metabolismo energético. Um estudo epidemiológico identificou que pessoas que permanecem acordadas de noite e dormem durante o dia apresentam 1,5 vezes mais chance de estar acima do peso do que aqueles que dormem de noite (Hulsegge, van Mechelen, Paagman, Proper, & Anema, 2020). A privação de sono noturno mostrou associações significativas com o aumento do IMC proporcional às horas de sono perdidas. Foi observado aumento de 0,43 kg / m2 a cada 10.000 horas acordados durante a noite (Peplonska, Bukowska, & Sobala, 2015). Foi destacado ainda chances 3,9 maior quando há restrição de sono noturno por oito ou mais dias por mês.
Aparentemente apenas os comportamentos considerados saudáveis como, a prática de atividade física, a qualidade do sono e os hábitos alimentares, não são suficientes para moderar a relação entre trabalho por turnos e excesso de peso, enquanto que os anos de exposição ao trabalho por turnos pode ser um fator moderador (Hulsegge et al., 2020). Assim, apenas os comportamentos de estilo de vida saudáveis podem, não ser suficientes para “proteger” contra os efeitos negativos da privação de sono noturno sobre o excesso de peso. Por outro lado, a obesidade é multifacetada e pode ser influenciada por determinantes sociais, de renda, nível educacional, conhecimento em saúde e apoio social (McGlynn et al., 2015).
The consequences of nocturnal sleep deprivation associated with a change in circadian rhythms impact not only body composition, but also health in general.
When night sleep deprivation is not caused by force majeure (night work), it is necessary to promote changes in lifestyle habits, especially regarding sleep hygiene (like avoiding stimulants such as caffeine at night), maintain regular sleep schedules, and avoid artificial lights during the night period. In addition, regular physical exercise and healthy eating can help in the process. In some cases, it may be necessary to resort to the use of medication, always with due medical supervision.