The deeper the sleep, the better the quality of sleep? How important is it to have a good night's sleep?

In October 2020, survey data from the China Sleep Research Society showed that the incidence of insomnia among Chinese adults was as high as 38.2%, which means that "more than 300 million people have sleep disorders (inability to fall asleep, inability to wake up, or poor sleep)". "Inability to fall asleep", that is, difficulty falling asleep (falling asleep time > 30 minutes) or difficulty maintaining sleep (difficulty falling asleep again after waking up), is the most common sleep problem. Sleeping pills are currently one of the mainstream ways to solve "inability to sleep". However, being able to fall asleep does not mean sleeping well. How can you get a good night's sleep?

Cognitive deep sleep

Snail Sleep pointed out in the "China National Healthy Sleep Insight Report" released on March 17 that healthy sleep requires the right time to fall asleep, sufficient sleep duration and high-quality deep sleep. Among them, deep sleep is one of the important indicators of a good sleep.

In 2007, the American Academy of Sleep Medicine divided the sleep process into wakefulness (W), light sleep (N1, N2), deep sleep (N3) and rapid eye movement (REM) sleep. Among them, deep sleep is also called slow wave sleep (SWS). Regardless of age, when slow wave activity accounts for more than 20% of a frame, it is judged as N3 [1]. Slow wave activity: The frequency is 0.5Hz~2Hz, and the amplitude of the positive and negative peak-to-peak interval measured in the frontal area is greater than 75uV, with the contralateral ear or mastoid electrode as the reference (F1-M1, F3-M2).

The duration of slow-wave sleep decreases with age[2]. Healthy young adults have about 2 hours of slow-wave sleep per night. Older adults (>65 years old) may only have about 1 hour of slow-wave sleep or none at all.

The peak secretion of pituitary growth hormone (GH) in normal adults occurs shortly after falling asleep. During sleep, approximately 70% of GH fluctuations occur during slow-wave sleep, and there is a positive correlation between the amount of GH secreted during GH fluctuations and the duration of slow-wave sleep [3].

Animal studies have shown that slow-wave sleep plays an important role in spatial memory that relies on the hippocampus, while both slow-wave sleep and REM sleep are required for procedural memory tasks that do not rely on the hippocampus. Studies on humans have shown that slow-wave sleep is more important for explicit memory (which relies on the hippocampus), while REM sleep is more important for implicit memory (which does not rely on the hippocampus)[4].

In 2019, researchers at Boston University monitored brain waves, blood flow, and cerebrospinal fluid activity during sleep. The results showed that when brain waves are slow, blood will periodically flow out of the brain in large quantities, and cerebrospinal fluid will flow into the brain in large quantities. After the cerebrospinal fluid flows in, it will remove toxins, such as beta-amyloid protein that causes Alzheimer's disease[5][6]. Some researchers believe that slow-wave sleep is a promising intervention target for Alzheimer's disease[7].

What are the factors that affect a good night’s sleep?

The "White Paper on Deep Sleep of Chinese Citizens" jointly released by Gujia Mattress and Snail Sleep points out that snoring and excessive dreaming are two major factors that hinder the quality of sleep of Chinese people. As people age, the proportion of snorers is gradually increasing; excessive fatigue, obesity, alcoholism, etc. are all inducing factors.

The factors that affect a good night's sleep are quite complex, and they are probably the following:

① Sleeping environment

A warm and comfortable sleeping environment is conducive to improving sleep quality and prolonging sleep time, including appropriate bedroom temperature and humidity, soft lighting, etc.

The indoor temperature should be between 20 and 23°C during sleep[8]. In summer, when the room temperature is 25°C, it is recommended to control the relative humidity between 40% and 50%; in winter, when the room temperature is 18°C, it is recommended to control the relative humidity between 50% and 65%[9]. It is generally believed that noise above 50 decibels will affect sleep. Long-term continuous noise will cause frequent dreams, easy awakening, and reduced deep sleep time. The light in the bedroom should not be too glaring, as excessive light will inhibit the pineal gland from secreting melatonin. Soft, dim light will promote sleep[10].

②Sleep hygiene habits

Good habits determine good sleep.

Regular work and rest is the most important sleep hygiene habit. Irregular work and rest time can lead to problems such as difficulty falling asleep, frequent awakening, early awakening, and poor sleep quality.

Don't eat or drink too much at night, especially fried, spicy and other irritating foods. Chinese medicine believes that "if the stomach is not harmonious, you can't sleep well", and only when the stomach and intestines are comfortable and harmonious can you ensure good sleep. Avoid strenuous exercise 3 hours before going to bed. Don't play with your phone or play games before going to bed. According to the data of Snail Sleep, the proportion of insomnia among people who play with their phones before going to bed is 13.4% higher than that of those who don't play with their phones.

③ Physical illness

Patients with chronic medical diseases often report insomnia symptoms, and the incidence of various medical diseases in people with insomnia is significantly higher than that in people without insomnia. Currently, more and more studies have confirmed that insomnia can increase the risk of diabetes, cardiovascular disease and cancer [11].

④ Mental disorders

About 70% to 80% of patients with mental disorders report insomnia symptoms, and about 50% of insomnia patients also suffer from a mental disorder (such as anxiety disorder, depressive disorder, bipolar disorder, schizophrenia, personality disorder, dementia, etc.). Among them, insomnia has a close and complex relationship with anxiety and depression. Soaking your feet before going to bed, listening to soothing music, or meditating for 30 to 45 minutes can help relax your body and mind and promote sleep.

⑤Others

Tobacco and alcohol

Nicotine in tobacco can cause the heart rate to increase and rapid brain wave movement, which can lead to difficulty falling asleep, fragmented sleep structure, reduced deep sleep, and easier awakening. Although drinking alcohol before bed can shorten the time it takes to fall asleep, it significantly reduces the time spent in deep sleep. In addition, alcohol is a diuretic, which can increase the number of times you wake up at night to go to the bathroom; alcohol can also relax the neck muscles, making snoring more severe for snorers. Generally speaking, people with poor sleep should not drink alcohol within 4 hours before going to bed [10].

bedding

Bedding that affects sleep mainly includes beds, mattresses, pillows, etc. The correct choice of bedding has an important relationship with sleep quality. The width of a bed should be 2.5 to 3 times the width of a person's shoulders. A bed that is too wide can easily make people feel uneasy, and a bed that is too narrow can easily cause people to fall out of bed or restrict their movements [10]. If the contact area between the body and the bed surface is too small, blood circulation in the affected area will be poor, leading to excessive tossing and turning at night and causing people to have shallow sleep. People who snore should not use pillows that are too high.

Sleeping position

For healthy adults, lying on the back is the best sleeping position[10]. Lying on the side will compress the lungs and heart, affect breathing, and easily lead to cardiovascular disease. However, for people who snore, lying on the back will aggravate snoring, and lying on the right side is the best sleeping position.

Overwork

Mild fatigue can help you fall asleep, but excessive fatigue can hinder your sleep. If you are still in a stressful working state before going to bed, you will easily wake up at night, and when you get up you will feel tired and have many dreams. Over time, this may lead to anxiety, insomnia, and even depression[10].

What are some ways to increase the proportion of deep sleep?

Data from Huawei Sports in 2017 showed that Chinese people are accustomed to falling asleep after 12 o'clock at night, nearly 70% of people have poor sleep quality, and only 26% of people have normal deep sleep.

Kong Xiang, the founder of Mumian, believes that to achieve deep sleep, one must pay attention to a comfortable sleeping environment, good sleep hygiene habits, and choose a mattress (moderately soft or hard), pillow, bedding, and even pajamas that suits oneself.

In addition, scientific diet and reasonable exercise are also very important for increasing the proportion of deep sleep.

①Scientific diet

First of all, you must eat breakfast. Skipping breakfast will disrupt your biological clock and easily lead to insomnia. Secondly, avoid drinking coffee after lunch and avoid consuming too much liquid or food before going to bed. Dinner is best to be had 2 to 3 hours before going to bed.

Excessive dreaming and shallow sleep are the sleep problems of most office workers nowadays. It is said that "dreams are good to have", but too many dreams are not good. Appropriate intake of some calcium-rich foods (such as dairy products, soy products), magnesium-rich foods (such as green leafy vegetables, bananas), tryptophan-rich foods (such as cereals, nuts) and other drinks (such as honey, tranquilizing flower tea), fruits (sour cherries, kiwis), etc. can improve sleep quality.

A study from Oxford University found that omega-3 helps the body achieve deeper, more restful sleep. Foods rich in omega-3 include pumpkin seeds, walnuts, salmon, and flax seeds. Dr. James Penland found that a diet high in magnesium and low in aluminum helps achieve deep, uninterrupted sleep. Green leafy vegetables, sesame seeds, etc. are concentrated sources of magnesium[9].

② Reasonable exercise

Exercise is one of the effective non-drug interventions and treatments for insomnia. Middle-aged women are advised to engage in moderate-intensity aerobic exercise (brisk walking) to improve sleep; the elderly are suitable for simple and easy-to-learn exercise methods to improve sleep quality, such as Ba Duan Jin [10].

On March 18, the China Sleep Research Society, De Rucci Bedding, and Keep jointly released the "2021 Exercise and Sleep White Paper". After analyzing the data, the white paper found that people who exercise for more than half an hour every day, especially those who get up early every day to exercise, choose swimming, basketball, badminton and other sports that mobilize the whole body muscles, and exercise regularly, are more likely to get good quality sleep.

③Others

Sound is an important factor in regulating sleep quality.

Papalambros NA et al. used a phase-locked loop method to precisely locate acoustic stimulation to the upper segment of slow sleep oscillations, which was able to enhance SWA and improve sleep-dependent memory storage in the elderly [12], as well as SWA in patients with amnestic mild cognitive impairment [13].

Temperature is another important factor in regulating sleep quality.

Studies have shown that a U-shaped change in ambient temperature during nighttime sleep is more conducive to improving sleep quality and work efficiency[14]. Ajwad A et al. used a closed-loop system to regulate ambient temperature to improve the sleep depth of mice[15]. In young people, especially healthy elderly people and insomniacs, intermittent increases in skin temperature during nighttime sleep can inhibit nighttime awakenings and shift sleep to a deeper stage. In addition, EEG spectrum analysis shows that increased skin temperature can enhance low-frequency cortical oscillations[16]. It is easy to get deep sleep when the temperature difference between daytime and nighttime is large. On the contrary, people who sleep shallowly are mostly because their body temperature is not high during the day and not low at night, and the temperature difference is small. Three major body temperature switches to improve sleep quality: bathing, foot bathing, and room temperature adjustment 90 minutes before going to bed[17].

summary

Whether it is to increase the proportion of deep sleep or to sleep well, in fact, it is necessary to attach importance to sleep strategically, that is, good sleep is an important cornerstone of physical and mental health, and to neglect sleep tactically, that is, sleep is a natural thing and the least effort. A relaxed attitude, a comfortable sleeping environment and bedding, good sleep hygiene habits, scientific diet and exercise are the guarantees of high-quality sleep. With them, sleep problems will no longer be a big problem.

References

[1] Berry RB, Brooks R, Gamaldo CE, Harding SM et al. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology, and Technical Specifications. v2.3. Translated by Gao He, Yin Guangzhong, et al. Beijing: People's Medical Publishing House, 2017.

[2] Carrier J, Viens I, Poirier G, et al. Sleep slow wave changes during the middle years of life. Eur J Neurosci. 2011;33(4):758-766.

[3] Zhao Zhongxin. Sleep Medicine. Beijing: People's Medical Publishing House, 2016.

[4] Ji D, Wilson MA. Coordinated memory replay in the visual cortex and hippocampus during sleep. Nat Neurosci. 2007;10(1):100-107.

[5] Fultz NE, Bonmassar G, Setsompop K, et al. Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science. 2019;366(6465):628-631.

[6] Grubb S, Lauritzen M. Deep sleep drives brain fluid oscillations. Science. 2019;366(6465):572-573.

[7] Lee YF, Gerashchenko D, Timofeev I, Bacskai BJ, Kastanenka KV. Slow Wave Sleep Is a Promising Intervention Target for Alzheimer's Disease. Front Neurosci. 2020;14:705.

[8] Zhao Zhongxin. The secrets of sleep and its regulation techniques. Beijing: Peking University Medical Press, 2013.

[9] Shawn Stevenson. Sleep Smarter. Translated by Chen Yaping. Changsha: Hunan Literature and Art Publishing House, 2017.

[10] Lu Lin. Guidelines for the comprehensive prevention and treatment of insomnia disorders in China. Beijing. People's Medical Publishing House, 2019.

[11] Zhang Bin. Chinese Guidelines for the Diagnosis and Treatment of Insomnia Disorders. Beijing: People's Medical Publishing House, 2016.

[12] Papalambros NA, Santostasi G, Malkani RG, et al. Acoustic Enhancement of Sleep Slow Oscillations and Concomitant Memory Improvement in Older Adults. Front Hum Neurosci. 2017;11:109.

[13] Papalambros NA, Weintraub S, Chen T, et al. Acoustic enhancement of sleep slow oscillations in mild cognitive impairment. Ann Clin Transl Neurol. 2019;6(7):1191-1201.

[14] Lan Li, Lian Zhiwei. Improving the thermal environment during sleep can improve sleep quality. Chinese Science Bulletin. 2020, 65(7): 533-534.

[15] Ajwad A, Huffman D, Yaghouby F, OrHara BF, Sunderam S. Sleep Depth Enhancement Through Ambient Temperature Manipulation in Mice. Annu Int Conf IEEE Eng Med Biol Soc. 2018;2018:1392-1395.

[16] Raymann RJ, Swaab DF, Van Someren EJ. Skin deep: enhanced sleep depth by cutaneous temperature manipulation. Brain. 2008;131(Pt 2):500-513.

[17] Nishino Seiji. Stanford High-Efficiency Sleep Method. Translated by Yin Fengzhu. Beijing: Cultural Development Press, 2018.