Brain Sleep Co., Ltd. (Headquarters: Chiyoda-ku, Tokyo; Representative Director: Kosuke Michibata; hereinafter "Brain Sleep"), with the cooperation of Kyoritsu Maintenance Co., Ltd., which operates the business hotel "Dormy Inn", conducted a study on the effects of sauna bathing on sleep (hereinafter "this initiative") in collaboration with 100plus Co., Ltd., represented by Mr. Hirotaka Kato, Representative Director of the Japan Sauna Academy, East Nippon Telegraph and Telephone Corporation, and NTT DX Partners Corporation (hereinafter "NTT East Group"). This study revealed that incorporating sauna bathing in addition to bathing before bedtime tends to improve both the duration and depth of deep sleep during the first sleep cycle, which plays the most crucial role in sleep quality, compared to bathing alone. Background of this initiative Brain Sleep is dedicated to solving Japan's sleep problems, which have the shortest sleep duration among OECD member countries, by developing products based on sleep medicine, disseminating accurate sleep information, and supporting the acquisition of sound scientific evidence related to sleep. In modern society, managing one's health is crucial and contributes to solving social issues. We believe that alleviating mental and physical tension through sauna bathing, which many people experience, could lead to improved sleep, and thus conducted this study to visualize its effects. Study Details and Results This study investigated the impact of sauna bathing, in addition to regular bathing, on sleep conditions. We measured and compared the sleep conditions of nine participants aged 20 to 60 after bathing alone versus bathing plus sauna. Sleep conditions were assessed using objective indicators such as activity trackers, autonomic nerve meters, and electroencephalograms, and subjective indicators through questionnaires using the VAS (Visual Analogue Scale) method. The results suggest the following possibilities for improving sleep quality through sauna bathing: ① Significantly improved sleep latency and sleep offset latency, indicating quicker sleep onset and easier waking. ② Tendency to improve deep sleep duration and depth during the most critical first 90 minutes of sleep (first sleep cycle). ③ Participants experienced "relaxation," "reduced fatigue," "refreshed awakening," and "vitality after waking." Result ①: Sleep latency and sleep offset latency, indicating quicker sleep onset and easier waking, significantly improved. Compared to the bathing-only group, the bathing-plus-sauna group showed significantly shorter sleep latency*1 and sleep offset latency*2. Although not statistically significant, the bathing-plus-sauna group showed a tendency towards improved sleep efficiency*3 compared to the bathing-only group. On the other hand, no clear differences were observed in the duration and frequency of wakefulness after sleep onset*4. *1 Sleep latency: The time taken from lying down to falling asleep. *2 Sleep offset latency: The time from final awakening to getting out of bed.*3 Sleep efficiency: The percentage of sleep time (excluding wakefulness after sleep onset) relative to the time spent in bed.*4 Wakefulness after sleep onset duration and frequency: The duration and number of times awake during the period from sleep onset to final awakening the next morning (total sleep time). Result ②: Deep sleep duration and depth in the most crucial first 90 minutes of sleep (first sleep cycle) showed an upward trend. Compared to the bathing-only group, the bathing-plus-sauna group showed a tendency towards increased Stage 3 sleep time (deep sleep duration) and delta power*5 (deep sleep depth) during the first sleep cycle. Schematic Diagram of Sleep Progression and Growth Hormone Secretion Overnight *5 Delta power is an indicator of the amount of delta waves, which are characteristic brain waves that appear during deep sleep in the first cycle, representing "sleep depth." Result ③: Participants experienced "relaxation," "reduced fatigue," "refreshed awakening," and "vitality after waking." In questionnaires administered to participants upon waking, statistically significant differences were observed between the bathing-plus-sauna group and the bathing-only group regarding "level of relaxation before sleep," "degree of fatigue reduction from sleep," "feeling of refreshed awakening," and "vitality after waking." Supplementary notes on the results Although this study involved a limited number of participants (9), as described in Result ① above, the bathing-plus-sauna group showed improved indicators related to sleep onset and waking compared to the bathing-only group, suggesting a high efficacy of sauna bathing on sleep. While statistically significant differences were not observed at a significant level for Stage 3 sleep time and delta power in the first cycle (described in Result ②), a tendency towards improvement was confirmed. It is believed that these effects could be substantiated by conducting further studies with a larger number of participants. Study Overview Participants: 9 individuals aged 20-60Study Method: Crossover studyMeasurement Items: Activity tracker, autonomic nervous system monitor, EEG, questionnaire evaluation using VAS (Visual Analogue Scale) methodLocation: Natural Hot Spring Ryoun-no-Yu Onyado Nono Asakusa (Dormy Inn / Onyado Nono Hotels Group) https://www.hotespa.net/hotels/nono_asakusa/ Comment from Hirotaka Kato, CEO of 100plus Inc. (Representative Director of Japan Sauna Academy) I believe many sauna enthusiasts feel that going to the sauna improves their sleep. However, there has been no detailed research on whether sauna truly improves sleep, or how it does so. This time, with the cooperation of Brain Sleep, Dormy Inn, and NTT East, we were able to visualize some of the effects of sauna on sleep. When we started this research, we usually compare it with cases where people don't go to the sauna. However, since many Japanese people take baths, we compared it with bathing. The research venue, "Nono" in Asakusa, has a black hot spring, so I was honestly concerned whether there would really be a difference between a hot spring versus a sauna + hot spring. However, the effects of the sauna were observed even with this strict comparison, which I think made the effects of the sauna even more prominent. I believe this is an important finding that confirms that going to the sauna truly improves sleep. We intend to continue this research to achieve a higher level of evidence. ＜Hirotaka Kato＞Born in Gunma Prefecture. Graduated from Hokkaido University School of Medicine. Doctor and PhD in Medical Science (specializing in pathology). After working as a specially appointed assistant professor at Hokkaido University School of Medicine, he moved to the United States. He worked at a hospital affiliated with Harvard Medical School, researching drug discovery for pancreatic cancer. After returning to Japan, he worked at the Cancer Center Genome Medical Unit at Keio University School of Medicine and the Institute of Oncology at Hokuto Hospital, where he practiced cancer genomic medicine. Witnessing the accelerating increase in medical expenses, he recognized the importance of preventive medicine. He established the Japan Sauna Academy to research sauna as a form of preventive medicine and founded 100plus Inc. to promote preventive medicine. He is the author of "The Sauna Textbook Taught by Doctors" (Diamond Inc.). Brain Sleep Co., Ltd. Chief Research Advisor / Seiji Nishino Comment While it is commonly heard in individual anecdotes that saunas have a positive effect on sleep, this has not been sufficiently scientifically verified, and its mechanism remains unclear. Sauna bathing often involves simultaneous bathing, so the effects of bathing on sleep also need to be considered. This verification experiment, although with a small number of subjects, confirmed that sauna bathing, apart from the effects of regular bathing, leads to quicker sleep onset, deeper sleep in the early stages of sleep, and improved awakening. Moving forward, it is hoped that the number of subjects will be increased to further examine the effects of sauna bathing on sleep in more detail, and that its mechanism of action will be elucidated. ＜Seiji Nishino＞Professor, Department of Psychiatry, Stanford University School of Medicine; Director, Stanford University Sleep & Circadian Neurobiology Laboratory. Founder and Chief Research Advisor, Brain Sleep Co., Ltd. Certified qualifications: Designated Mental Health Physician, Japanese Society of Sleep Research Certified Sleep Specialist, Industrial Physician, Physician, Doctor of Medical Science. Joint Research Partners 100plus Co., Ltd. (https://www.100plus.info)Head Office Location: Nerima-ku, TokyoEstablished: July 2021Representative: Hirotaka Kato, Representative DirectorBusiness Activities: Wearable device development, vital data collection, algorithm development East Nippon Telegraph and Telephone Corporation (https://www.ntt-east.co.jp/)Head Office Location: NTT East Headquarters Building, 3-19-2 Nishi-Shinjuku, Shinjuku-ku, TokyoEstablished: July 1999Representative: Naoki Shibuya, President and CEOBusiness Activities: Regional telecommunications services*7 in the East Japan region*6 and related services, objective achievement services, utilization services. *6 Hokkaido, Aomori Prefecture, Iwate Prefecture, Miyagi Prefecture, Akita Prefecture, Yamagata Prefecture, Fukushima Prefecture, Ibaraki Prefecture, Tochigi Prefecture, Gunma Prefecture, Saitama Prefecture, Chiba Prefecture, Tokyo Metropolis, Kanagawa Prefecture, Niigata Prefecture, Yamanashi Prefecture, and Nagano Prefecture. *7 Telecommunications services such as telephone, leased lines, and integrated digital communications for inter-prefectural calls. NTT DX Partners Corporation (https://www.nttdxpn.co.jp/)Head Office Location: NTT East Headquarters Building 9F, 3-19-2 Nishi-Shinjuku, Shinjuku-ku, TokyoEstablished: January 2022Representative: Tamaki Endo, President and CEOBusiness Activities: DX consulting / DX implementation and promotion support / System operation, data analysis, and other outsourced services / Co-creation support / All businesses incidental or related to the above, etc. Kyoritsu Maintenance Co., Ltd. (https://www.kyoritsugroup.co.jp/)Head Office Location: 2-18-8 Sotokanda, Chiyoda-ku, TokyoEstablished: October 1979Representative: Koji Nakamura, President and CEOBusiness Activities: "Dormitory business" managing student and employee dormitories / "Hotel business" managing business hotels and resort hotels / "Senior life business" managing residences for the elderly / "PKP (Public Kyoritsu Partnership) business" supporting public services in collaboration with local governments
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