The aim of this study was to elucidate the level of daytime sleepiness in Japanese school-aged children and adolescents, and to examine associated factors including sleep loss and social jetlag using the Japanese version of the Pediatric Daytime Sleepiness Scale (PDSS-J). After the linguistic validation of the PDSS-J with a multi-step translation methodology, consisting of forward translation, back translation, expert review and cognitive debriefing interviews, we conducted a psychometric validation for 492 students aged 11–16 years (46.7% boys) of public elementary school, junior high school and high school, using the PDSS-J, the Karolinska Sleepiness Scale (KSS), and bedtimes and wake-up times on school days and free days. Internal consistency (Cronbach’s alpha) of the PDSS-J was 0.77, and the test–retest reliability demonstrated by the intraclass coefficient was 0.88. Multivariate logistic regression analysis revealed that both short sleep duration and social jetlag were identified as factors associated with daytime sleepiness, after adjustment for age and sex. PDSS-J scores were significantly higher in the group with large social jetlag with or without sufficient sleep duration than in the group with sufficient sleep duration and small social jetlag. The PDSS-J is an important tool for assessing daytime sleepiness, given its ease of administration and robust psychometric properties. The impact of not only sleep loss but also social jetlag on daytime sleepiness among school-aged children and adolescents must be fully taken into account.

Sleep problems are known to be risk factors for subsequent emotional and behavioral difficulties in childhood and adolescence. To date, there has been no study investigating the relationships between sleep habits and behavioral problems in a large nonclinical sample of preschool age children. The aim of this study was to examine these relationships and factors associated with the sleep habits of preschool age (2 to 5 year old) children. Their mothers (n = 1,746) completed a multiple-choice questionnaire about the sleep habits and behavior problems of their children, as well as their own sleep habits and working hours at Tokyo metropolitan public nursery schools. The short sleep duration group showed significantly higher aggressive scores than the long sleep duration group among 2- to 3-year-old children, and the irregular bedtime group showed significantly higher aggressive and attention problem scores than the regular bedtime group among 4- to 5-year-old children. Univariate and multivariate logistic regression analyses revealed that children's late bedtime was associated with their mother's late waking-up time, and late schedule of both the mother's leaving and returning home. This study recognized an association between behavioral problems and poor sleep habits among preschool-age children. It is important for children to sleep regularly and adequately in order to decrease their behavior problems. In conclusion, appropriate management of children's sleep by their mothers is necessary for promoting sleep-related health of children.

Several studies have reported that short sleep duration is a risk factor for obesity and metabolic disease. Moreover, both sleep duration and sleep timing might independently be associated with dietary nutrient intake. In this study, we investigated the associations between self-reported sleep duration and dietary nutrient intake, with and without adjustments for variations in sleep timing (i.e., the midpoint of sleep). We conducted a questionnaire survey, comprising a validated brief self-administered diet history questionnaire (BDHQ) and the Japanese version of the Pittsburgh Sleep Quality Index (PSQI) among 1902 healthy Japanese adults and found that the dietary intakes of several nutrients correlated with sleep duration among men regardless of adjustment for the midpoint of sleep. Particularly, (1) small but significant correlations were observed between sleep duration and the percentage of energy from protein, regardless of adjustment for the midpoint of sleep; (2) energy-adjusted intakes of sodium, vitamin D, and vitamin B12 also significantly correlated with sleep duration; and (3) intakes of bread, pulses, and fish and shellfish correlated with sleep duration. In contrast, no significant correlations were observed between sleep duration and dietary intakes among women. This study revealed that after controlling for the midpoint of sleep, sleep duration correlated significantly with the dietary intake of specific nutrients and foods in a population of Japanese men.

Previous studies have suggested that patients with obstructive sleep apnea syndrome (OSAS) are at an increased risk of motor vehicle accidents (MVAs). This study is the first systematic investigation of MVA risk among Japanese drivers with obstructive sleep apnea syndrome (OSAS). We investigated the rate of MVAs in the preceding 5 years and dozing off at the wheel in Japanese male OSAS drivers (n = 616, mean [S.D.] age: 46.3 [10.1] years old) and age-matched male controls (n = 600), and the characteristics of OSAS patients who experienced multiple MVAs as well as the effectiveness of continuous positive airway pressure (CPAP) treatment in reducing MVA risk. The odds ratio of MVA in the OSAS group compared to a general population was 2.36. Multivariate logistic regression analysis revealed that MVA was significantly associated with either subjective sleepiness beyond normal limits (Epworth sleepiness scale: ESS ≥ 11) or serious respiratory disorders (apnea hypopnea index: AHI ≥ 40). AHI scores were significantly higher in the group with multiple MVAs than in those with a single MVA, despite the ESS score in the former group being significantly lower. CPAP treatment was effective for reduction of MVA. The MVA rate among OSAS patients in the research area was significantly higher than that among the controls. Subjective excessive daytime sleepiness and severity of OSAS are independently associated with the occurrence of MVA. In conclusion, early diagnosis and treatment of OSAS drivers especially with serious respiratory disorder should be made to prevent multiple MVAs.

Longitudinal studies in Japan indicate that nocturnal sleep onset has become later and sleep duration has been progressively shortened. This study aimed to investigate the relationship between sleep patterns and sleep problems among children, and to determine the association between parents and their children's sleep habits. Questionnaires about sleep problems and life habits were administered to families living in Tokyo metropolitan areas of Japan. We analyzed the data of pre-school-age (1-5 years old; n = 319, including 175 girls) and elementary school-age children (6-11 years; n = 217, including 116 girls) as well as their parents (402 mothers: 37.0 ± 4.9 years, 402 fathers: 39.0 ± 5.9 years). Subjects were categorized as morning (evening) type when they answered their lifestyle habit as “definitely or moderately morning (evening) type”. Sleep was categorized into regular, irregular, and intermediate from the sleeping-waking regularity scores. The frequency of daytime dozing is significantly high in children with evening-irregular sleep. Moreover, mothers of children (aged 1-5 and 6-11 years) with evening-irregular sleep have significantly more irregular sleep habits than those of children with morning-regular sleep. Likewise, fathers of children (aged 1-5 years) with evening-irregular sleep have significantly more irregular sleep habits. Thus, irregular late bedtime of parents is associated with sleep problems, daytime sleepiness, and irregular dietary habits of children. Mothers' sleep habits have a stronger influence on their children's sleep than fathers'. Our study indicates the importance of promoting sleep hygiene that encourages healthy sleep for all family members.