Four-year-olds with shorter than average sleep times have more behaviour problems, exhibiting aggression and throwing tantrums, a new study has found.
"Preschool children with shorter nighttime sleep duration had higher odds of parent-reported overactivity, anger, aggression, impulsivity, tantrums, and annoying behaviours," according to the study by Dr Rebecca J Scharf of University of Virginia, Charlottesville, and colleagues.
The researchers analysed parent responses from a 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 behaviour questionnaire, parents rated their child on six different "externalising" behaviour problems such as anger and aggression.
Externalising behaviour problems are outward behaviours, distinguished from "internalising" 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 nighttime sleep duration of about ten and a half hours. Eleven per cent of children were considered to have "short sleep duration" of less than 9 hours (calculated as one standard deviation below the average).
On the child behaviour questionnaire, 16 per cent of children had a high score for externalising 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," Scharf and colleagues said.
The effect was greatest for aggressive behaviour problems, which were about 80 per cent more likely for children with nighttime sleep duration of less than 9 hours.
Shorter sleep times were also associated with 30- to 46-per cent increases in rates of the other externalising behaviours studied, including overactivity, anger, impulsivity, tantrums, and annoying behaviours. In a linear analysis, as sleep duration increased, troubling behaviours decreased.
Although the study can't draw any conclusions about causality, "there is good reason to believe that short nighttime sleep duration leads to externalising behaviours," the researchers wrote in the Journal of Developmental & Behavioral Pediatrics.