Cultural Approaches to Addressing Sleep Deprivation and Improving Sleep Health in Japan: Sleep Issues Among Children and Adolescents Rooted in Self-Sacrifice and Asceticism

1. Sleep in Japan Before the Emergence of Yōjōkun

Classical Japanese literature, terms such as "nemachizuki" and "fushimachizuki" were used to refer to times indicative of bedtime. These elegant expressions refer to the moon visible four days after the full moon of the eighth month in the lunar calendar (the 19th day of the moon) [44]. The names are believed to have originated from the custom of going to bed when the moon finally rose in the evening. The earliest record of "nemachizuki" appears in the 25th chapter of Tōtō Nikki, dating back to 957 AD [45]. According to calculations by the National Astronomical Observatory of Japan [46], the moonrise on the 19th day of the eighth lunar month in 957 occurred at 20:32, which corresponds to the time for sleeping or retiring for the night, suggesting that it reflects the bedtime of the aristocracy in the Heian period. For reference, sunset on that day was at 17:56, indicating that Heian aristocrats likely went to bed approximately 2.6 hours after sunset.

In the book Early Rising [47], the warrior Tōdō Takatora (1556–1630), who was active during the Sengoku and early Edo periods, wrote, "One should rest by 8 PM." Furthermore, a passage from the book Bushikokoroe is quoted, advising, "One should go to bed early at night." Based on the title, this book is thought to have been written in the early Edo period. During this period, the health benefits and restorative effects of sleep were widely emphasized, with similar descriptions found in the Korean medical text Dongui Bogam, which was well-known in Japan [48]. In the early Edo period, there seems to have been no widespread tendency to undervalue sleep.

2. Yōjōkun

Yōjōkun is a widely known text in Japan [49]. The author, Kaibara Ekiken (1630–1714), was a Confucian scholar based in Fukuoka during the Edo period. Yōjōkun was written in 1712 when Kaibara was 83 years old, based on his own experiences. The philosophy of Yōjōkun seeks to explore the methods and techniques for promoting physical and mental health and achieving longevity. Its intellectual roots are traced to the natural philosophy of Laozi, and its fundamental principles can be seen in the opening lines of the Huangdi Neijing Suwen, which state: "Eating and drinking in moderation, maintaining regularity in daily activities, and avoiding excessive labor" [50]. In Chapter 23, "Xuanming Wuqi Pian" of Huangdi Neijing Suwen, it is written that "Excessive sleep depletes the qi," warning against oversleeping. This caution aligns with recent epidemiological studies, which have revealed that insufficient sleep increases the risks of obesity, ischemic heart disease, cerebrovascular disorders, type 2 diabetes, hypertension, and mortality [51,52]. On the other hand, excessive sleep has also been associated with higher risks of these conditions and mortality [52,53]. While the exact reasons for this relationship remain unclear, it appears that achieving an individual's OSD minimizes the risks of illness and death. Chapter 2, "Si Qi Tiao Shen Da Lun", recommends sleep patterns according to the seasons. In spring and summer, it suggests a later bedtime and earlier wake-up time, while in autumn, one should go to bed early and wake up early. In winter, bedtime should be slightly earlier, and wake-up time later, aligning with sunrise and sunset. This advice is consistent with a study conducted on 55,000 individuals in Germany, which showed that sleep duration fluctuates with the seasons, being 20 minutes longer in winter than in summer [54]. Additionally, research on hunting-gathering societies in Africa and South America found that they woke up before dawn and went to bed approximately 3.3 hours after sunset [55], which means winter sleep duration was about one hour longer than in summer. Huangdi Neijing reflects these natural human tendencies, not undervaluing sleep. Recent studies have also suggested a relationship between sleep duration and lunar phases, with sleep duration being longest before the new moon and shortest before the full moon [56], though this connection is not mentioned in Huangdi Neijing.

In contrast, Yōjōkun tends to undervalue sleep. To put it drastically, the underlying message of Yōjōkun is "Do not sleep." Kaibara Ekiken served the Kuroda clan and also lectured in Confucianism. Moreover, during the early Edo period, the concept of explaining the lord-servant relationship through Zhu Xi's Confucianism was established by figures such as Yamaga Sokō. Confucianism emphasizes asceticism and spiritual cultivation, and it is believed that this asceticism is reflected in Yōjōkun.

In Yōjōkun, sleep is mentioned 16 times across eight volumes. It is noted that overeating, excessive drinking, and excessive sleep can harm one's health. In particular, Volume 1, Section 24 warns, "Excessive sleep causes illness and shortens life." In Section 28, it is encouraged to reduce sleep in order to improve health, asserting that the need for sleep decreases with willpower. Kaibara Ekiken seems to view sleep as a passive activity, not acknowledging its active role. In contrast, in Huangdi Neijing's Ling Shu, sleep is recognized not merely as a countermeasure against wakefulness, but as an active process that requires energy (qi). In Volume 2, Section 1, it is stated, "Do not lie down and relax after meals. Resting or sleeping for long periods will disturb your mood and lead to illness." Section 6 advises against napping during long summer days, and Section 16 emphasizes that an important aspect of a healthy life is to avoid lying down at inappropriate times and ensuring proper meals. Section 17 states, "Food nourishes the body, while sleep nourishes the mind," and continues, "Those who practice proper health management rise early, sleep late at night, do not nap during the day, avoid overeating, and maintain discipline in their sleep and eating habits. This is the foundation of a healthy life." Ultimately, Section 51 concludes, "Reducing desires, not worrying, keeping the body active through work, and minimizing sleep are the four fundamental principles of a healthy life." In Volume 4, Section 34, it advises against lying down after eating, which contrasts sharply with the common Edo period saying, "A nap after meals is the best remedy for all diseases." Post-meal sleepiness may be linked to decreased orexin secretion associated with an increase in blood glucose levels [57]. Lying down might promote parasympathetic nervous system dominance, which could aid digestion. While the exact reason for avoiding post-meal naps is unclear, if we adhere to the guidance from Yōjōkun, it may align with recent chronobiological findings suggesting that late-night meals are harmful. In Volume 5, Sections 6 and 7, there are instructions regarding sleep posture and the number of times one turns over during sleep—matters that are difficult to consciously control. Section 8 warns about exposure to light during the night, advice that remains relevant today. Section 29 offers practical guidance, stating that one should not be exposed to wind during sleep. However, in Section 32, it repeatedly states, "Even if you feel drowsy after eating, you should not lie down." In Volume 6, Section 9, it teaches that "The bedroom should protect against wind, cold, heat, and humidity, and should always remain comfortable."

Why did Yōjōkun adopt such a dismissive stance toward sleep? One important factor is that Ekiken belonged to the samurai class. The samurai were a group whose profession was warfare, and within this group, the concept of "Bushidō" (the Way of the Warrior) developed [58]. The term Bushidō is first recorded in the early Edo period in Kōyō Gunkan [59]. It is likely that Kaibara Ekiken was familiar with Kōyō Gunkan. With the advent of the Edo period, intense warfare subsided, and the samurai no longer needed to refine their combat skills. As a result, the samurai spirit shifted from martial techniques to Bushidō, which became increasingly refined. Bushidō is characterized by the spirit of self-sacrifice, exemplified by the well-known practice of seppuku (ritual suicide). The ideology of the ruling class gradually permeated the common people. Yōjōkun, which incorporates not only the principles of Zhu Xi’s Confucianism but also the spirit of Bushidō, likely spread to the general population.

3. From Yōjōkun to the End of World War II

The 1832 publication Byōka Suchi [60], Japan's first home medical encyclopedia and guide for home nursing, recommends going to bed early at night and rising before sunrise. From a modern perspective, this advice reflects a more balanced view of sleep. The author, Hirano Shigeaki, was born into a samurai family but did not take up a public office, instead dedicating himself to treating the common people as a town doctor. His approach contrasts with the spiritual perspective of Yōjōkun, suggesting a shift in views on sleep in the broader social context.

In Hito to Tegami [61], written about the author of Nanso Satomi Hakkenden, Takizawa Bakin (1767–1848), it is stated that "Bakin and his family strictly adhered to a bedtime of 10:00 PM for many years". Additionally, Bakin’s diary records, "Due to today’s heat, I stopped writing and spent the day reading. I went to bed around 8:00 PM." This suggests that Bakin's habits were not aligned with the principles in Yōjōkun.

The Iyo History Association website [62] introduces a diary written by Saionji Genjūrō, a figure involved in the Uwajima Domain during the late Edo period, covering June 1 to June 6. According to this diary, during these six days, the individual did not stay awake past 10:00 PM, indicating that the late Edo society was not universally affected by sleep deprivation, contrary to the warnings of Yōjōkun about excessive sleep.

During the Meiji period, prominent figures also took sleep seriously. Fukuzawa Yukichi was known to go to bed by 10:00 PM, and Morimura Shizaemon, based on personal experience, recommended 8 hours of sleep [47]. In 1912, a popular elementary school song, Mura no Kajiya, depicted a blacksmith maintaining his health through regular sleep patterns [63]. Additionally, the rules of the Early Rising Youth Association, founded in 1920, encouraged waking up early while also emphasizing that securing 8 hours of sleep was essential for health maintenance [47].

In the late Meiji period, with the advancement of modernization, Ninomiya Sontoku (also known as Kanjiro) became an influential figure regarding sleep. Descriptions of him can be found in elementary school choral songs [64] from 1911 and in elementary school morality textbooks [65] from 1918. In these descriptions, his early-life efforts, diligence, and self-reliance are emphasized, portraying him as an idealized figure embodying perseverance and moral virtues. From 1924 onwards, Ninomiya Sontoku became a symbol of Japan’s moral education, with statues erected in schools across the country [66]. He is often depicted reading while keeping a fire burning, emphasizing diligence and self-sacrifice through late-night studying and early rising. However, this portrayal lacked biological or empirical evidence regarding the influence of circadian rhythms or sunlight on sleep cycles. Instead, it reflected Confucian and Bushidō-based ascetic and moralistic ideologies, which implicitly spread the undervaluation of sleep by associating laziness with poor moral character.

Within the historical context in which self-sacrifice and asceticism were highly valued, a critical remark on sleep appears in a 1939 publication [67]. The author states: “I often encounter individuals who pride themselves on their sleep, yet such people frequently lack mental clarity even when awake and tend to doze off during conversations. These individuals are akin to those who eventually get run over by a car” [67].

4. After World War II

Before World War II, asceticism based on Confucian principles and Bushido was strongly emphasized in Japan, and it was expected that a backlash would occur following the country’s defeat in the war. However, the 1948 school anthem “Song of Youth”, created by my alma mater, included the phrase "Furei kokku", meaning "strive with effort" [68]. This phrase is derived from the power of will emphasized by Mencius. In Confucianism, following Mencius' teachings, the pursuit of personal moral cultivation and academic achievements was emphasized. Japan, long influenced by strong will and asceticism, continued to press forward even after the war, with a trend of reducing sleep hours that persisted in the post-war era. As symbolized by the 1989 slogan "Can you fight for 24 hours?" [3], Japan rapidly advanced toward becoming an economic powerhouse. This social trend is likely tied to the spirit of Bushidō as well.

The tragic case of Matsuri Takahashi, a Dentsu employee who died by suicide due to overwork in 2015 [69], has become an important theme in my lectures at the women's university. Reflecting on Matsuri's case, especially when observing students of a similar age, I am always strongly reminded that we must not let history repeat itself. One student’s reflection after a lecture noted the pressures that new employees face, the sense of responsibility toward their work, and the inability to ask for help. The student also mentioned that living alone, like Matsuri, can lead to being overlooked and not receiving support, which could result in similar tragic outcomes. This response highlights the importance of mental health support systems in the workplace. Below is an excerpt from a student’s writing: “The headline of a reference article, 'You may be pushing someone to their limits' [70], was shocking. I was surprised to learn that 90,000 people a year are involved in re-delivery, with approximately 10% of delivery workers spending time on it. Also, the words of a former Dentsu employee resonated with me: 'Clients are treated like 'gods,' while staff and subcontractors meet unreasonable demands through inhumane efforts. But they are also human. Even seemingly trivial demands can take someone’s time and push them to their limits. Everyone should imagine that.'"

5. Conclusion

Looking back at the history of sleep undervaluation in Japan, it becomes clear that this attitude is rooted in the aesthetic of self-sacrifice and asceticism, first exemplified in Yōjōkun. The author posits that this book may represent an early manifestation of Japan’s tendency to undervalue sleep in contemporary society. While there have been periods when the importance of sleep was emphasized, the general attitude in Japanese society has not been to revere sleep, often viewing it as a form of laziness. This attitude is not simply the result of Yōjōkun itself but stems from Japan’s unique, irrational metaphysical aesthetics—namely, the cultural acceptance of self-sacrifice and asceticism. The deeply ingrained spirit of Bushidō also plays a role in maintaining and supporting this concept of self-sacrifice. Transforming such deeply rooted cultural values is not easy, but recognizing that this cultural background is at the root of sleep deprivation in Japan is crucial to mitigating the harmful effects of sleep deficiency. Of course, sleep deprivation among children and adolescents is a global issue, and addressing it solely through Japan’s unique cultural lens may present challenges. However, Japanese educators must recognize that in order to improve the sleep of future generations, they must break free from the tradition of revering self-sacrifice and asceticism that has unconsciously permeated their own culture.