The purpose of this study was to examine mattress comfort in terms of subjective handling of the material, sinkage, firmness, elasticity (resilience), warmth,turning over, and width (size), and proposed a causal model of overall sleeping comfort. For this study, 240 subjects (120 males and 120 females) between the ages of 20 and 49 were surveyed via a web-based questionnaire. The survey included basic information on gender, age, region, height, weight, scoliosis, physical condition, and the material, size, and thickness of the mattress they were using.Multiple regression analysis revealed that four factors were significantly related to overall comfort: sinkage, elasticity (resilience), width (size), and warmth. For overall comfort, sinkage was most strongly related, and there was also a strong relationship between sinkage and resilience. In addition, the results of examining the effects of physical information such as BMI and scoliosis on sleep comfort suggested that the subjective satisfaction with the mattress may be influenced not only by the material factors of the mattress but also by the physical characteristics of the user. Furthermore, results of present study suggest that combination of multiple physical characteristics may influence sleeping comfort.

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The cessation of the nap habit in early childhood is one of the developmental stages of sleep rhythm. The current "Guideline for Education and Care of Certified Centers for Early Childhood Education and Care (ECEC)," revised in 2018, clearly states that "consideration should be given not to uniformly apply the nap since the time spent at centers differs and the sleep time varies depending on the developmental status of children and individuals," but the actual conditions of nap are still unknown. This study aimed to investigate the current conditions and issues regarding naps during 3 to 5 years of age depending on the management structure of certified centers for ECEC based on a national survey in Japan. The results of the national survey for 2,209 certified centers for ECEC revealed that among 1,236 certified centers that provide afternoon nap for 5-year-old children, 80% of public centers, 50% of school corporations, and 70% of social welfare centers reported that "children who do not want to sleep also go to their beddings", indicating that many of the centers still have a uniform system of afternoon nap. In preparation for the future revision of the guidelines, it is expected to deepen the discussion on the nap and to provide training opportunities to these certified centers.

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Midafternoon sleepiness frequently occurs independently of lunch or lack of sleep, suggesting an association with biological rhythms. One effective strategy to counteract this sleepiness is taking a nap. However, naps exceeding one hour can increase the risk of various health issues and cause grogginess upon awakening, known as sleep inertia. Additionally, lengthy naps often disrupt nighttime sleep. These adverse effects arise from the occurrence of slow-wave sleep (Sleep Stage N3) during the nap. In contrast, short naps lasting approximately 15 to 20 minutes can avoid slow-wave sleep, thereby minimizing adverse effects and enhancing benefits such as decreased sleepiness and improved performance. Although short naps primarily involve sleep stages N1 and N2, only N2 contributes to the restorative benefits of napping, with N1 providing minimal effectiveness. Nevertheless, sleep inertia can still occur after short naps. Several countermeasures are explored to mitigate this inertia, such as arousal stimuli, caffeine intake, or self-awakening techniques.

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DST (Daylight Saving Time, commonly known as Summer Time) is a time system in which the clocks are set forward by one or two hours from the standard time for each country or region in the summer. DST in Europe and the United States was established about 100 years ago in order to request for cooperation in the World War. As the health problems have become apparent in modern society, both Europe and the United States are moving toward abolishing DST, but as of 2024, it has been continued. Japan has not adopted DST except for a few years after the World War II, but unless DST is abolished in Europe and the United States, it is predicted that there will be a movement to introduce DST in Japan again in the future. However, considering Japan's latitude, hot and humid weather, electricity demand, modern short-sleep sleeping habits, and diversification of lifestyles, the introduction of DST in Japan is not possible to bring any “benefits” such as heat countermeasures, electricity and energy conservation, or creating leisure time, but rather is predicted to have adverse effects such as increased working hours, health problems including sleep, and confusion in database management. Therefore, in modern Japan, it can be concluded that DST is an unnecessary, harmful and useless “fraudulent” time system, and that its introduction should be firmly opposed.

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Climate change, such as global warming, can affect the sleeping environment especially during summer. Although the effects of summer heat are often explained by maximum outdoor temperatures, minimum outdoor temperatures are also increasing, and tropical nights have been recorded at many observation points in Japan. Therefore, this paper provides an overview of climate change, especially during the summer nighttime, are based on the effects of global warming and urban heat island (UHI) in several cities and relationship between these factors and sleep. Furthermore, it introduces the Sleep-Index, which allow us to adjust the thermal environment of our bedrooms based on the outdoor weather conditions. Finally, we analyzed the time-series of changes in page views of the Sleep-Index website, finding that the page views of the Sleep-Index website increased rapidly, when there was a sudden rise in the maximum or minimum outdoor temperature followed by the maintenance of high temperature. We also found that the page views of the Sleep-Index website under the COVID-19 pandemic were significantly higher during the period of dusk until dawn, than for the other contents of tenki.jp.

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The purpose of this study was to examine the moderating effect of mindfulness on the process from Big Five personality traits and chronotype to insomnia tendency in university students. The participants of the analysis were 127 university students (mean age 19.81 ± 1.23 years). A simultaneous multi-population analysis was conducted by dividing the study subjects into a low mindfulness group (n = 68) and a high mindfulness group (n = 59) based on their mindfulness scores. The analysis revealed that both groups showed a significant positive association between conscientiousness and chronotype. However, the low mindfulness group exhibited a significant negative association between chronotype and insomnia tendency, while the high mindfulness group showed no significant association between chronotype and insomnia tendency. These results indicate that mindfulness has a moderating effect in the process model of this study, suggesting that when mindfulness is cultivated, even if low conscientiousness is associated with eveningness, it is unlikely to lead to insomnia tendency.

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Sleep-related attentional bias is considered to play a key role in the development and maintenance of chronic insomnia disorders. The purpose of this study was to develop the lists of sleep-related words and neutral words for use in a cognitive task to assess attentional bias. In Study 1, twenty-four lists (24 sleep-related words and 120 neutral words) were extracted using the “Association Frequency Table” and the “Balanced Corpus of Contemporary Written Japanese”. In Study 2, the survey (n = 300) regarding the extent to which these words are related to sleep was conducted. The results showed significant impression rating differences between sleep-related words and neutral words in all lists. It is expected that these lists will be used as a reference for developing a cognitive task to evaluate attentional bias toward sleep-related stimuli in the future.

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