Children who are bullies or have conduct problems at school are more likely to be sleepy during the day, according to University of Michigan Medical School researchers.

Researchers looked at elementary school students in the Ypsilanti, Mich, public schools who had exhibited conduct problems like bullying or discipline referrals and found that there was a twofold higher risk for symptoms of sleep-disordered breathing, particularly daytime sleepiness, among these students. The study was published in the journal Sleep Medicine.

"What this study does is raise the possibility that poor sleep, from whatever cause, can indeed play into bullying or other aggressive behaviors—a major problem that many schools are trying to address," says Louise O’Brien, PhD, assistant professor in U-M’s Sleep Disorders Center and the Departments of Neurology and Oral and Maxillofacial Surgery.

"Our schools do push the importance of healthy eating and exercise, but this study highlights that good sleep is just as essential to a healthy lifestyle."

O’Brien said the study showed that sleepiness seemed to be the biggest driver of the behavior problems, not the snoring, which is often a more obvious symptom associated with sleep-disordered breathing.

The sleepiness experienced by the children in the study could be caused by sleep-disordered breathing, but also by many other factors like chaotic home environments, fragmented sleep, or not enough sleep because of too much electronic stimulus from televisions, cell phones, or computers in the bedroom, says O’Brien.

O’Brien says that a longitudinal study is needed. Although there are other reasons for these behaviors, if sleepiness does contribute to aggressive behavior as this study suggests, a significant proportion of bullying in children might be eliminated by efforts to reduce children’s daytime sleepiness.