A new study has found that 4-year-olds with shorter than average sleep times have increased rates of "externalizing" behaviour problems.

"Preschool children with shorter night time sleep duration had higher odds of parent-reported overactivity, anger, aggression, impulsivity, tantrums, and annoying behaviours," according to the new research by Dr. Rebecca J. Scharf of University of Virginia, Charlottesville, and colleagues.

They recommend that parents and health care providers discuss steps to improve sleep habits for preschool-age children with behaviour problems.

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, night time sleep duration was estimated by asking the parents what time their child typically went to bed and woke on weekdays.

On a standard child behaviour questionnaire, parents rated their child on six different "externalizing" behaviour problems such as anger and aggression. (Externalizing behaviour problems are outward behaviours, distinguished from "internalizing" problems such as depression and anxiety.)

The relationship between sleep duration and behaviour scores was assessed, with adjustment for other factors that might affect sleep or behaviour.

The average bedtime was 8:39 pm and wake time 7:13 am, giving a mean night time sleep duration of about 10 and a half hours. Eleven percent of children were considered to have "short sleep duration" of less than 9 hours 45 minutes (calculated as one standard deviation below the average).

On the child behaviour questionnaire, 16 percent of children had a high score for externalizing behaviour problems.

Behaviour 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 behaviour than children with longer sleep duration," Dr Scharf and colleagues write.

The effect was greatest for aggressive behaviour problems, which were about 80 percent more likely for children with night time sleep duration of less than 9 hours and 45 minutes.

The study is published in the Journal of Developmental and Behavioral Pediatrics, the official journal of the Society for Developmental and Behavioral Pediatrics.