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

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.