Association of nighttime sleep with behaviors in Japanese early childhood.

Background: Preschool children in Asian countries, including Japan, sleep for a shorter duration at night than those in Europe and the USA. We examined the effects of the nighttime sleep duration on behavioral development in early childhood in Japan.

Methods: We used data from a large Japanese nationwide, population-based, longitudinal survey that began in 2001. We restricted the study participants to children born after 37 gestational weeks, with a birth weight ≥ 2500 g and singleton births (n = 41 890). The nighttime sleep duration was examined at 2.5 years old. Responses to survey questions regarding age-appropriate behavior at 5.5 years old were used as indicators of behavioral development. We conducted logistic regression analyses with adjustment for confounding factors, with ≥11 h of nighttime sleep as the reference group.

Results: The odds ratios for children who had ≤9 h of nighttime sleep, which was associated with being unable to listen with fidgeting and being unable to remain patient, were 1.26 (95% confidence interval, 1.14-1.39) and 1.27 (1.16-1.38), respectively. Children who had an irregular nighttime sleep duration were associated with age-appropriate behavioral inabilities. These results were similar in children who usually and sometimes took naps to those before stratification by the frequency of napping.

Conclusion: A short nighttime sleep duration especially affects hyperactivity and impulsivity. An irregular nighttime sleep duration increases the inability to perform overall age-appropriate behaviors more than a short sleep duration. Ensuring a regular and sufficient nighttime sleep duration in early childhood is important for healthy behavioral development.