Text | Sun Jie, Lu Lin
Sleep is a fundamental process of life and a cornerstone for maintaining physical and mental health. March 21 this year is the 24th World Sleep Day, and the theme in China is "Healthy Sleep for All". The main purpose is to arouse the attention of the whole people to the importance of healthy sleep, so that they can obtain correct scientific knowledge of healthy sleep, and realize the sleep health of "Healthy China".
About 1/3 of a person's life is spent sleeping. As an important and complex physiological process of the body, sleep is essential for maintaining physical and mental health, and is an indispensable physiological process for human beings.
Healthy sleep includes light sleep, deep sleep, and rapid eye movement (REM) sleep. These sleep cycles last about 90 minutes, alternating until you wake up.
Lack of sleep can adversely affect the health of the body, leading to decreased cognitive function, immune system dysfunction, increased incidence of tumors and increased risk of cardiovascular disease. The survey results show that the incidence of insomnia among Chinese adults is as high as 38.2%, and more than 300 million Chinese have sleep disorders, and this number is still rising year by year.
Sleep disorders, such as insomnia, have always been a complex and common problem, and their causes are unknown. It is generally believed that insomnia is closely related to the stress, bad lifestyle habits and psychological conditions faced by individuals, and that factors such as stress can lead to brain dysfunction, which in turn leads to sleep regulation disorders.
However, recent research has found an unexpected link – sleep disorders such as insomnia may be significantly associated with an imbalance in the gut microbiota.
Early research suggests that eating habits may have an important impact on sleep. Some dietary patterns affect not only people's alertness during the day, but also the quality of sleep at night. In addition, consuming specific foods before sleep can help improve sleep quality. For example, a high-protein diet can help promote deep sleep, making it easier to fall asleep and be awakened at night. This is because protein intake stimulates the gut to produce a special substance that allows people to sleep better by reducing the brain's sensitivity to external stimulus signals.
It can be seen that in addition to the composition of the food itself, the microbes in our gut are also actively involved in the sleep regulation process, communicating with our brain, and this magical connection is the so-called gut-brain axis.
Historically, bacteria were thought to be the culprits of disease, but now we must realize that there are bacteria that are not only harmless to humans, but also vital to life. Our bodies are surrounded by a large number of microorganisms, which are even more than 10 times the number of our own cells. These trillions of microbes cover our bodies from the inside out, forming a complex ecosystem.
Experts estimate that at least 35,000 different bacteria, fungi and viruses in the human gut live in symbiosis with humans. Since each microorganism contains its own DNA, the total number of bacterial genes encoded by gut microbes is 100 times greater than the total number of human genes.
Modern medicine has found that the gut microbiota, a vast community of microorganisms that live in our bodies, has become part of the body and should be considered an "organ". The existence of intestinal microbes is not only an inevitability, but also a health guarantee. We have developed a close symbiotic relationship with these microbes since birth.
Studies have shown that gut microbes not only play an important role in the establishment of gastrointestinal function, body metabolism and immune system formation and regulation, but also regulate brain nerve function, mood and behavior. There are about 100 billion neurons in the human brain and 500 million neurons in the gut, and the microbiome-gut-brain axis is the communication network that connects the central nervous system to the gut.
There is growing evidence of a complex interaction between sleep and the gut microbiota that affects sleep quality and physical health. The gut microbiota can be regulated by the microbiome-gut-brain axis and sleep.
There is a close interaction between the gut microbiota and sleep, both of which have rhythmic activity and are influenced by external factors. The early stages of life are critical stages in the establishment of microbiota, and the duration of infants' daytime sleep is inversely correlated with the diversity of gut microbes.
Studies in preschool-aged children have shown that sleep time is associated with the diversity of the gut microbiota, with a higher relative abundance of Bifidobacteria in children with longer total nighttime sleep. Studies in adult subjects found a positive correlation between microbiome diversity and total sleep time. In patients with chronic insomnia, the diversity and composition of the gut microbiome changed significantly, the diversity of the microbiome decreased, the relative abundance of lactobacilli was negatively correlated with the regional uniformity value, and the number of beneficial bacteria decreased and the number of harmful bacteria increased. In this case, supplementing with probiotics can help restore normal sleep.
Sleep is essential for health, and sleep deprivation or irregularity not only affects concentration and mood, but also has an impact on the gut microbiome. Studies have shown that sleep deprivation and sleep restriction reduce the diversity of gut microbes and significantly alter the composition of microorganisms. These changes can be reversed after supplemental sleep.
It is important to note that not only sleep deprivation, but also irregular sleep can have a negative impact on the intestinal flora. This disturbance of the microbiota may increase people's risk of obesity, as well as diabetes, cardiovascular disease, and neurodegenerative diseases. Therefore, maintaining good sleep habits is essential for maintaining gut health and human health.
The gut microbiome plays an important role in sleep regulation. They affect sleep quality in a number of ways.
First, the gut microbiota can secrete melatonin, serotonin, orexin, histamine, and short-chain fatty acids, which can affect sleep by acting on receptors in the brain. If the intestinal flora is disturbed, the levels of metabolites produced by it will be imbalanced, which in turn will affect sleep.
Secondly, the gut microbiome can communicate with the brain through the vagus nerve and regulate the expression of neurotransmitters in the brain, affecting the ratio of non-REM sleep to REM sleep. Stimulation of the vagus nerve increases REM sleep percentage.
Finally, gut microbes can also regulate sleep by influencing immune levels. It was found that transplanting fecal bacteria from insomnia patients into germ-free mice could induce sleep disturbances in germ-free mice and increase the levels of inflammatory factors such as serum interleukin-6.
Understanding the relationship between sleep and your gut microbiota, and taking appropriate adjustments, can help improve sleep quality and overall health. We can try the following ways to regulate the gut microbiome and promote a good night's sleep: consume probiotics and prebiotics, eat more foods rich in dietary fiber, such as fruits, vegetables and whole grains to promote the growth of good bacteria, reduce stress and relax through meditation and moderate exercise, maintain a regular schedule, and maintain a regular wake-up and bedtime to help maintain the ecological balance of the gut microbiome.
In exploring the influence of the gut microbiota on sleep, we should not only understand brain function, but also comprehensively explore the complex and amazing biological systems of the human body. By understanding the role of the gut microbiome, we may be able to find a more natural and effective solution to sleep problems than traditional medications.
(Sun Jie is the deputy chief physician of Peking University Third Hospital, Lu Lin is an academician of the Chinese Academy of Sciences and president of Peking University Sixth Hospital)