Influence of sleep-onset time on the development of 18-month-old infants: Japan Children’s cohort study

Abstract

Objective

We report here the influence of sleep patterns on the development of infants in Japan. A total of 479 infants were registered in two different Japanese cities. Direct neurological observations were performed by licensed pediatric neurologists.

Method

We designed a prospective cohort study and identified the sleep factors of children showing atypical development. The Kinder Infant Developmental Scale (KIDS) was used to evaluate the infant developmental quotient (DQ); we also applied a neurobehavioral screening battery. Neurobehavioral observations in 18-month-old infants were designed to check all developmental categories within the three areas of motor function, language, and social function. Based on the observations, each infant was classified as having “atypical development” or “typical development”.

Result

We found that later sleep onset time (>22:00 h), and longer naps during the day each had significant positive correlations with atypical development patterns in 18-month-old infants. For each hour the infant sleep-onset time extended past 22:00 h, the infants showed worse neurodevelopmental outcomes, at an odds ratio increase of 2.944.

Conclusion

Although our results may be confounded by sleep problems resulting from pre-existing developmental disabilities, we can safely conclude that appropriate sleeping habits are important for healthy development in 18-month-old infants.

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.