NEW YORK: A preference for nighttime over daytime activities may be associated with antisocial behaviour in adolescences, even in children as young as 8-years-old, according to a new study. Those who prefer later bedtimes appear to exhibit more antisocial behaviour than those who like to wake early and participate in daytime recreational activities, researchers report.

Study co-author Elizabeth J Susman, of Pennsylvania State University, said, staying up late "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 and her team investigated the relationship between a preference for morning versus evening activities and antisocial behaviour in 111 subjects between 8- to 13-years-old. They also correlated morning to afternoon cortisol levels with behaviour and noted the age at which the subjects reached puberty. The researchers found a number of factors were related to antisocial behaviours in the study group, particularly in the boys who tended to exhibit more rule-breaking behaviours than did their peers. The findings are published in the Developmental Psychology journal.

For girls, a preference for evening activities was associated with a higher incidence of relational aggression or aggressive behaviour towards their peers. Boys who experienced prolonged high levels of cortisol-smaller decreases in cortisol levels from the time of awakening until 4 pm-tended to have more behaviour problems than did their peers, the report indicates. This was not true for girls, however.

Normally, levels of cortisol, the stress hormone associated with circadian rhythms, peak in the morning upon awakening and plateau during the afternoon and evening hours.

Boys who hit puberty at earlier ages tended to also engage in more rule-breaking and attention behaviour problems than did other boys, according to parent reports, and they self-reported more symptoms of conduct disorder. Girls who were younger at puberty reported more relational aggression compared with their peers, study findings indicate. Overall, the findings imply that "caregivers should be vigilant to bedtime activities of children and young adolescents," Susman said.