A new study in the July issue of the Journal of Developmental & Behavioral Pediatrics reports that shorter than average sleep times may contribute to “externalizing” behavior problems in young children.

“Preschool children with shorter nighttime sleep duration had higher odds of parent-reported over-activity, anger, aggression, impulsivity, tantrums, and annoying behaviors,” according to research by Dr. Rebecca J. Scharf of the University of Virginia, Charlottesville, and colleagues.

The researchers analyzed parent responses from a nationally representative study of approximately 9,000 children, followed from birth through kindergarten age. When the children were four years old, nighttime sleep duration was estimated by asking the parents what time their child typically went to bed and woke on weekdays.

On a standard child behavior questionnaire, parents rated their child on six different externalizing—or outward—behavior problems such as anger and aggression. The relationship between sleep duration and behavior scores was assessed, with adjustment for other factors that might affect sleep or behavior.

The average bedtime was 8:39 pm and wake time 7:13 am, giving a mean nighttime sleep duration of about 10½ hours. Approximately 11% of children were considered to have “short sleep duration” of less than 9¾ hours (calculated as one standard deviation below the average). The average 10½-hour sleep time in this nationally representative sample is less than in studies performed in past decades, and less than currently recommended for four-year-olds.

On the child behavior questionnaire, 16% of children had a high score for externalizing behavior problems. Behavior problems were more common for boys, children who watched more than two hours of television daily, and those whose mothers reported feeling depressed.

After adjustment for other factors, “Children in the shortest sleep groups have significantly worse behavior than children with longer sleep duration,” Dr Scharf and colleagues write. The effect was greatest for aggressive behavior problems, which were about 80% more likely for children with nighttime sleep duration of less than 9¾ hours.

Shorter sleep times were also associated with 30% to 46% increases in rates of the other externalizing behaviors studied, including over-activity, anger, impulsivity, tantrums, and annoying behaviors. In a linear analysis, as sleep duration increased, troubling behaviors decreased.

The new results, along with other recent studies, add to the evidence that preschoolers who sleep less will have more behavior problems, including disruptive behaviors like aggression and over-activity. Dr Scharf and coauthors recommend that parents and health care providers discuss steps to improve sleep habits for preschool-age children with behavior problems.