Sleep Health

In Greek mythology, Hypnos, the god of sleep, is depicted as a gentle deity holding a poppy flower, bringing peace and rest to the weary.

From ancient times to the present, humans' need for sleep has never changed, but our understanding of it has been constantly deepening. In the past few decades, scientists have gradually revealed the genes, molecules, cells, and neural circuits behind sleep regulation, yet they still can't fully answer this seemingly simple question: Why do we need sleep?

In today's fast - paced life, more and more people choose to sacrifice sleep in exchange for so - called "efficiency." Will this bring irreversible effects?

As the "World Sleep Day" on March 21 approaches, perhaps it's time to re - examine this daily phenomenon closely linked to life and think about how to safeguard this precious gift from nature in our busy lives.

I. Why Do We Sleep

With the help of external or internal electrodes, sleep can be monitored and segmented. The sleep of vertebrates is usually divided into non - rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). As a task that takes nearly one - third of a lifetime to repeat, sleep is destined to play some key roles. The need for sleep may originate at the cellular level. After being awake for a long time, neurons show signs of fatigue, but not all areas of the brain need "sleep." Since birth, the neural circuits controlling breathing have been working non - stop until the end of life.

The fundamental reason and mechanism for why humans need to sleep remain a controversial issue in neuroscience to this day. Short - term sleep deprivation affects cognitive ability and mood, and long - term sleep - deprived individuals even have a significantly higher incidence of dementia, which means that long - term sleep deprivation may be related to pathological changes in the brain. However, simply regarding the adverse effects of sleep deprivation as the reason for sleep is not sufficient. A more likely theory is that sleep can provide the body with the necessary structural or metabolic processes for a healthy brain/body.

The necessary repair and cleaning mechanisms after sleep can help the brain "clean up redundancies" after a busy day, thus ensuring the normal metabolism and function of the brain the next day. This may be explained by the temporary loss of consciousness during sleep.

The "lymphatic hypothesis" mechanism suggests that during NREM sleep, lymphatic flow can be accelerated to help remove brain metabolites. During wakefulness, metabolites such as Tau protein and amyloid protein related to Alzheimer's disease gradually accumulate. During sleep, the production rate of these substances may decrease or even stop, providing an opportunity for the body to clear them. Previous studies have also found that the clearance of β - amyloid protein in the brains of mice peaks during sleep, and the content of β - amyloid protein in the human brain increases after sleep deprivation [1].

In addition, other hypotheses include synaptic remodeling, the reduced brain temperature during NREM sleep to help brain repair, and the current oscillations during NREM and REM periods to balance the neural network [1]. Although science has revealed many mysteries of sleep, the exploration of the fundamental question of "why humans need to sleep" continues, and every peaceful night's sleep awaits us to uncover more answers.

II. What Is Sleep Health

The concept of "sleep health" is undergoing an important cognitive transformation. Recently, the National Health Commission released the "Core Information and Explanation of Sleep Health," which not only systematically elaborates on the profound impact of sleep on the functions of various human systems but also emphasizes that sleep health should be considered from a full - life - cycle perspective [2].

Buysse's RU - SATED model also divides sleep health into six dimensions: regularity, sleep satisfaction, alertness, timing, efficiency, and duration [1].

The importance of regular work and rest for health has been fully verified. Research shows that irregular sleep is significantly associated with many chronic diseases such as type 2 diabetes, which may be due to the disorder of the biological clock leading to the dysregulation of the stress response of cells and organs. In particular, it is recommended that adults go to bed between 10 - 11 p.m. and get up between 6 - 7 a.m., which not only conforms to the human physiological rhythm but also maximizes the repair function of sleep [2].

Although the sleep duration varies from person to person, there is still a scientific range. Currently, it is generally believed that adults should ensure 7 - 8 hours of night sleep. It is worth noting that from infants to the elderly, the sleep demand shows a gradual decreasing trend: newborns may need 13 - 18 hours, while the elderly may only need 6 - 7 hours [2]. However, in today's fast - paced society, even if people know these standards, few can actually achieve them.

The evaluation criteria for sleep quality are also constantly being improved. Good sleep should be characterized by falling asleep within 30 minutes, waking up no more than 3 times at night and being able to fall asleep again quickly, and feeling energetic after waking up [2]. These objective indicators are as important as subjective sleep satisfaction because they may reveal some sleep problems that are difficult to detect by instruments.

III. What Are the Effects of Sleep Deprivation?

Current research has confirmed that sleep has an all - around impact on the human body. Poor sleep habits increase the risk of cardiovascular diseases, metabolic disorders, and low immune function. More alarmingly, sleep problems are closely related to mental health problems such as depression and anxiety, and may even affect cognitive function and memory. The Health Commission specifically points out that long - term poor sleep also reduces work efficiency and increases the risk of safety accidents.

Research has found that sleep deprivation increases the desire of humans and many species to catch up on sleep (similar to the need for food and water when hungry and thirsty), and it takes a longer time to make up for the lost sleep, which may also indicate that there are necessary synthesis, metabolism, and other repair processes during sleep. After sleep deprivation, the amplitude of the delta wave on the electroencephalogram will increase significantly and rebound quickly, which may be a sign allowing subsequent repair mechanisms such as brain cooling [1].

However, the specific biochemical processes in the brain for tracking wake - time and controlling sleep desire are still unclear. Some scholars believe that the conversion of the sleep - wake cycle may involve the increase or decrease of the concentration of a certain substance in a specific area of the brain, but the current hypotheses such as adenosine, IL - 1β, TNF - α, etc. cannot give a satisfactory explanation for all situations. Whether peripheral tissues such as muscles are auxiliary factors for sleep drive cannot be excluded at present [1].

Sleep is also an important stage for the excretion of brain metabolic waste. During wakefulness, metabolites such as Tau protein and amyloid protein gradually accumulate. During sleep, the production rate of these substances may decrease or even stop, providing an opportunity for the body to clear them. Previous studies have also found that the clearance of β - amyloid protein in the brains of mice peaks during sleep, and the content of β - amyloid protein in the human brain increases after sleep deprivation.

How does the brain achieve a high rate of waste clearance during sleep? The increase in extracellular volume during sleep and the resulting increase in molecular transport rate may be one of the promoting factors. The change in the fluid flow pattern during sleep is also a possible mechanism. During the NREM sleep stage, the flow wave of cerebrospinal fluid is more obvious, and this flow is driven by low - frequency neural activity. Neural activity can regulate blood volume, thereby accelerating the flow and renewal of cerebrospinal fluid [1].

A study by Tatia Lee's team at the University of Hong Kong in 2025 found that poor sleep quality in the elderly leads to impaired lymphatic system function, causing the accumulation of harmful substances in the brain, affecting the function and structural connection of memory - related brain regions (such as the middle temporal gyrus and parahippocampal gyrus), and ultimately leading to memory decline. On the contrary, people with good sleep quality can effectively clean up brain waste through the lymphatic system and maintain normal memory function through the neural network coupling mechanism [3].

However, the more detailed relationship between the flow of cerebrospinal fluid, the renewal of solutes in tissues, and brain health, as well as the contribution of different sleep stages to brain fluid flow, still need to be further clarified by future research. Whether the cerebrospinal fluid flow promoted by neural activity forms a two - way closed - loop promoting sleep and neural activity is also an interesting research topic. We should also be vigilant about the vicious cycle of sleep deprivation or poor sleep and reduced clearance or increased production of metabolic waste [1].

IV. Can Drug Intervention Improve Sleep Quality

Improving sleep quality requires a multi - pronged approach. At the individual level, innate factors such as age, gender, and genes all affect sleep conditions. But more importantly, it is the acquired behavioral interventions, such as avoiding staying up late, controlling the use time of electronic products, and maintaining moderate exercise. The standards of sleep environment temperature (20 - 24°C) and humidity (40% - 60%) recommended by the Health Commission also provide specific references for improving sleep quality [2].

Can the use of sedative drugs for sleep - aid provide the repair effect of natural sleep?

The results of functional magnetic resonance imaging during NREM sleep are similar to those after dexmedetomidine/propofol anesthesia. This may be related to the fact that both sedatives and anesthetics act on the components of the sleep - wake cycle such as the lateral habenula, ventral tegmental area, and hypothalamus. However, drugs can hardly simulate the performance of REM sleep. Although they all act on the sleep cycle, there are significant differences between sedation/anesthesia and sleep. This also explains why the recovery after anesthesia is far from as refreshing and comfortable as waking up from a natural sleep, and most of the time it is accompanied by unpleasant experiences [1].

Whether sedative/anesthetic drugs can provide a repair effect is still unknown. The electroencephalogram can only provide very limited information in this regard and is easily affected by confounding factors. Trauma caused by factors such as surgery may mask the manifestation of the repair effect. Moreover, the repair effect of normal sleep still needs to be refined, and quantitative measurement is still a pipe dream. However, based on the fact that sedation cannot simulate the normal NREM - REM sleep cycle, it can be inferred that current drugs cannot simulate natural sleep. The GABAergic neurons in the ventral tegmental area can promote sleep homeostasis and may be potential targets for sedatives that can provide a repair effect in the future.

V. Can Technology Decode Sleep

Sleep research is entering a critical breakthrough period. With the integration of molecular biology, neuroscience, and artificial intelligence technology, we have not only revealed the physiological mechanism of sleep but also touched the boundary between consciousness and subconsciousness.

Especially in recent years, the global public health crisis and the subsequent transformation of social lifestyles have made sleep problems a focus of attention for both the scientific community and the public. From the high - frequency citations in academic journals to the continuous discussions on social media, sleep research is moving from the laboratory to the public eye at an unprecedented speed, and this interaction in turn promotes the deepening and expansion of research directions.

Empowered by technology, sleep research is moving from the laboratory to the real world. Wearable biological monitoring devices allow us to glimpse the uniqueness of individual sleep patterns, and artificial intelligence algorithms help us find patterns in massive data. However, does this quantification and standardization of sleep also imply a simplification of human experience? When we reduce sleep to a set of measurable indicators, do we ignore its rich connotation as a life experience?

In the 24/7 modern society, sleep seems to be the opposite of efficiency. But history tells us that humans' attitude towards sleep has never been one - dimensional: from the ancient Greeks regarding sleep as a bridge connecting the real world and the ideal country to the view of sleep as a production factor to be optimized after the Industrial Revolution. Each era re - defines the meaning of sleep, and the mission of our era may be to find a balance between technological progress and human needs.

This exploration is far from over. Every new discovery expands our understanding of ourselves and consciousness. Perhaps in the near future, we will not only have a better understanding of sleep but also glimpse the essence of human cognition and the deep connection between technology and life.