Study Objectives: To examine the longitudinal and bidirectional association between nighttime sleep duration and emotional and behavioral problems (EBPs) over 15 months among preschool children.

Methods: Data of children aged 2 to 6 years from the control group of the Danish Healthy Start Study, a 15-month obesity prevention intervention, were used. Nighttime sleep duration was measured using a 7-day sleep record. EBPs were assessed by the Strengths and Difficulties Questionnaire Total Difficulties (SDQ-TD) score and Prosocial Behavior (SDQ-PSB) score. Multivariable regression models were conducted to examine the bidirectional associations between changes in nighttime sleep duration and SDQ scores.

Results: With adjustment for child, family factors, and parental stress level, every hour extra nighttime sleep at baseline was associated with a 1.02 decrease in SDQ-TD score and 77% lower odds of having an abnormal SDQ-TD score (>= 90th percentile) at the follow-up (p = 0.01). Children who increased their nighttime sleep duration over the 15-month demonstrated a similar concurrent reduction in SDQ-TD score (beta = -1.28, p = 0.02) compared with those who decreased or had no change in nighttime sleep duration. After additional adjustment for sleep problem and habit variables, the significant associations remained. No associations were found between nighttime sleep duration and SDQ-PSB scores. Examination of SDQ scores as predictors of subsequent changes in nighttime sleep duration showed no significant associations.

Conclusions: Among preschool children, longer nighttime sleep duration was associated with a decline in EBPs, but not vice versa. Our study provides new longitudinal evidence to support sleep interventions to improve EBPs in early childhood.