Youths who like to stay up late at night are more prone to antisocial behaviour, rule-breaking and attention problems, according to a new study.

In their examination of 111 boys and girls aged eight to 13, researchers at Penn State University tried to understand how a characteristic called "morningness/eveningness" influences young adolescent behaviour.

"The link between eveningness preference and antisocial behaviour was previously associated only with older adolescents," said study author Elizabeth J. Susman, whose findings appear in the July 2007 issue of Developmental Psychology. "The novel finding of the study is that the link is now apparent as early as eight-year-old kids."

Morningness or eveningness refers to individual differences in sleep-wake patterns, as well as preferences for activity and alertness in the mornings and evenings.

Results from Susman's study suggest that evening activity is correlated to antisocial behaviour, rule-breaking, attention problems and conduct disorder in young boys. For girls, it is associated with feelings of isolation and "relational aggression" — behaviour that is meant to hurt another child's friendship.

She warns that an early preference for evening activity could have a serious impact on a child later in life, and that parents should encourage their children to sleep early and for an adequate number of hours.

"Eveningness contributes to lack of sleep, and this in turn causes problems such as lack of control and attention regulation, which are associated with antisocial behaviour and substance use," Susman said.

Researchers are also studying how puberty and a hormone called cortisol influence adolescent behaviour. In humans, Cortisol regulates such behavioural traits as the fight-or-flight response and immune activity, as well as learning and memory.