Obesity has a multiple etiology, meaning many factors influence its development. The most relevant are overeating, lack of physical activity, ethnicity and personal genetics, certain pathologies, and nighttime sleep hours. We know that lack of sleep has a negative impact on a person’s physical and emotional well-being, and it has also been found to be closely linked to obesity in both children and adults. Epidemiological studies conducted in developed countries indicate that chronic sleep loss can increase the risk of developing obesity.
Normal sleep organizes itself into two phases: the NREM (non-rapid eye movement) phase, which takes up three-quarters of total sleep time and supports physical rest, and the REM (rapid eye movement) phase, which makes up the remaining quarter and contributes to mental function, making it essential for psychological and emotional rest as well as memory. During sleep, these two phases alternate in cycles healthy individuals typically experience four to five sleep cycles.
How does sleep affect our weight?
Adequate sleep plays a vital role in maintaining the normal functioning of the neurological, endocrine, metabolic, immune, and cardiovascular systems. It also supports psychological and emotional well-being. Therefore, when people experience disrupted sleep, it harms their overall health and quality of life, and insufficient sleep alters their appetite, increases hunger, and changes energy expenditure. According to researchers at Brigham and Women’s Hospital in Boston, the resting metabolic rate, which constitutes between 60% and 70% of daily energy expenditure in most sedentary adults, varies according to the circadian rhythm.
Sleep restriction reduces metabolic rate and, with it, decreases the calories we burn at rest, which is an energy-saving mechanism that could be the cause of weight gain. The human body uses a 24-hour rhythm that regulates the wake-sleep process. This rhythm has been termed circadian (it refers to the physical, mental, and behavioral changes that follow a daily cycle and respond primarily to light and darkness in an organism’s environment). The hypothalamus controls this rhythm and synchronizes it not only with the light/dark cycle but also with environmental factors such as slumber habits and temperature.
How much sleep do we need?
Modern lifestyles encourage nocturnal activities. Electric lights, television, and computers offer new generations the opportunity for nighttime entertainment and have displaced the pleasure of sleep. Researchers have identified that the current general population, including children, now sleeps one and a half to two hours less than they did in the 1960s. They have linked this change to increased appetite and subsequent weight gain. Changes in the metabolism of hormones that regulate appetite and reduce energy expenditure may cause this relationship between less sleep and increased appetite.
Hormonal rhythms also follow a circadian pattern regarding their secretion and function, and this pattern is also susceptible to alteration when the circadian rhythm of slumber is disrupted. For example, the hormone somatropin (STH) peaks 1/2 hour after bedtime, while prolactin peaks 40 minutes after the first hour. In contrast, thyroid hormone (TSH) and cortisol disappear at the onset of sleep. The amount of slumber (total slumber time) needed is individual, so some people slumber five hours or less and others need more than nine hours to feel good.
Screen time and sleep
There are three types of slumber patterns: a short sleep pattern (<6 hours), an intermediate slumber pattern (6-8 hours), and a long sleep pattern (>8 hours), although sleep quality must also be taken into account. Sleep quality is a subjective characteristic, and there can be people with an efficient or good-quality slumber pattern and those with an inefficient or poor-quality pattern. Researchers hypothesize that short slumber duration affects the regulation of energy balance. Furthermore, altered levels of hormones that control appetite—such as increased ghrelin and decreased leptin (an appetite-suppressing hormone)—can partly explain the relationship between short slumber and weight gain.
Sleep deprivation lowers leptin levels and increases ghrelin levels. The brain receives signals that the body is hungry, thus increasing food intake. In a controlled study in a healthy male population, sleeping an average of only four hours was found to be associated with a significantly greater desire to eat high-calorie foods. The purpose of this review is to present to the academic community recent evidence suggesting a relationship between poor sleep quality and quantity and a propensity for overweight and obesity.
Conclusion
This paper presents evidence from controlled clinical studies and experimental basic research demonstrating that poor slumber quality or quantity leads to short-term metabolic and behavioral alterations leading to overeating and overweight. Researchers also discuss possible mechanisms underlying this phenomenon at the brain, metabolic, and cellular levels. The objective of this review is to present slumber hours as a factor under-considered in epidemiological and experimental studies and a potential trigger for metabolic alterations.
With this paper, we hope to interest other professionals involved in the study of this phenomenon to include sleep quality and quantity among their study variables and/or to include slumber hygiene among their treatment and prevention proposals. The aim of this review is to highlight recent evidence that links poor slumber quality and quantity with an increased propensity to develop overweight or obesity. In this text, we present evidence obtained from controlled clinical studies as well as experimental models, both indicating that decreased sleep hours lead to metabolic and behavioral changes that then induce overconsumption of food, which then results in weight gain.
