Original articleInfluence of sleep-onset time on the development of 18-month-old infants: Japan Children’s cohort study
Introduction
During the period of early infancy, sleep patterns begin to change dramatically [1], [2], [3]. Sleep deprivation and other sleep problems in children caused by factors such as late sleep onset and curtailed nocturnal sleep are a major public health concern in Japan and worldwide [4], [5]. Sleep problems in adolescents and adults have also increased worldwide. Despite these sleep-related health concerns, relevant epidemiological studies have been limited, with very few being comprehensive enough to show a correlation between sleep status and mental, cognitive, behavioral, and/or physical health; further, only a few of these have been prospective cohort studies [6], [7], [8], [9]. We therefore designed a prospective study to investigate the relationship between sleep status and social competence in Japanese infants [10]. This study was based on the understanding that incomplete acquisition of social competence underlies social problems in children, resulting in irritability, school refusal, mild developmental disorders, adolescent delinquency, social withdrawal, infant care anxiety, and child abuse [11], [12].
While some manuscripts report that the development of sociality in children is affected by individual factors such as temperament and inborn growth/development properties, others emphasize environmental factors such as family and social environment, behaviors of parents, and the mother–child relationship [13], [14], [15]. The development of sociality in children is known to be affected by a combination of biological and psychosocial factors; however, its relation to sleep patterns remains insufficiently researched.
Previous cohort studies seeking to identify the underlying cause of specific problems in children have not included direct developmental and behavioral observations in collaboration with pediatric neurologists or psychologists. Recently, late onset and shorter sleep periods have been tentatively linked to the cognitive and behavioral functions of infants and children [16], [17]. Children with autism spectrum disorder (ASD) or attention deficit hyperactivity disorder (ADHD) have shown higher rates of nonstandard sleep factors [18], [19], [20], [21], [22], [23], [24]. However, only a few studies have been designed as prospective cohort studies, and most of these were based on questionnaires. We therefore designed a cohort study that relied on direct evaluation of behavior, including minor neurological signs, to evaluate the relationship between sleep patterns and child development. We hypothesized that sleep patterns, especially late sleep-onset time resulting in a shorter night’s sleep, would show deleterious effects in the development of 18-month-old infants.
Section snippets
Participants
The Japan Children’s Study (JCS) is a unique prospective cohort study that commenced in 2005 and was conducted by the JCS research group at two study sites in Japan. The JCS was designed to assess factors affecting development in children, in particular those affecting social skills (children’s sociability) [10]. Infants born between 2004 and 2005 together with their parents were selected from two sampling areas, Osaka and Mie City, to participate in this study. The developmental ages of
Sleep schedules
In the present study, we used the Japan Children’s Study Sleep Questionnaire (JCSSQ) to evaluate infant sleep patterns at the age of 18 months. JCSSQ is a unique questionnaire that allows the parameters of “wake time”, “bed time”, “number of nights waking”, “nap time” and so on to be addressed for weekdays, Saturdays, and Sundays using three separate timelines in a form that is simple and easy for caregivers to fill in (Fig. 1) [25], [26]. Therefore, we evaluated the sleep diary data for
Neurodevelopmental assessments at 18 months of age
Serial observations were done in 403 infants from 479 families (follow-up rate; 84.1%). Of these, 300 infants were evaluated as having typical development, and 80 were evaluated as having atypical development. We diagnosed 19 children as having deviated development, and 61 children as having imbalanced development, based on the neurobehavioral observations. Then, we confirmed similar tendencies in sleep items and other background items. Finally, we performed statistical analysis on the combined
Discussion
The present study showed that the development of 18-month-old infants is affected by their sleeping habits. Later sleep-onset time (>22:00 h), and longer naps during the day showed significant associations with atypical development patterns in 18-month-old infants. In our cohort study, all infants were assessed for development and classified, not only by the KIDS B, but also by licensed Japanese neuro-pediatricians through observations. This direct examination for infant’s development leads to a
Contributors
Mizue Iwasaki, Akiko Iemura, collected the data and wrote this manuscript, Noriko Yamakawa performed and directed the Mie district study, Kiyotaka Tomiwa performed the Osaka cohort study, Yoko Anji and Yoichi Sakakihara designed the method for direct neurological examination, including examination of soft neurological signs of 18-month-old infants, and analyzed the samples. Shinichiro Nagamitsu did statistical analysis and contributed to writing the manuscript. Tatsuyuki Kakuma performed the
Acknowledgments
We thank and are deeply indebted to the participating children’s parents and the administrators of the Japan Children’s Study. This study is based on the mission-type research project conducted by the RISTEX (Research Institute of Science and Technology for Society) and the Japan Science and Technology Agency.
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Cited by (0)
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Akiko Iemura and Mizue Iwasaki contributed equally as first co-authors.