This cross-sectional study in an urban public school district found that schoolchildren with conduct problems or school discipline referrals, in comparison to peers, have increased symptoms of SDB. The results were robust, in that high SDB risk on a well-validated questionnaire was twice as common among children with symptoms of conduct problems, as compared to children without. However, sleepiness rather than a symptom more specific to SDB -- snoring -- appeared to drive the association between SDB risk and aggressive behaviors. Parent-reported bullying, though not teacher-reported bullying, showed similar associations with SDB symptoms. Our study was cross-sectional and cannot prove causality, but dose-response findings were consistent with the hypothesis that SDB, and sleepiness in particular, could contribute to conduct problems in schoolchildren. Although previous literature has reported aggressive behavior as a possible symptom of SDB17, 19, 20
, we now suggest more broadly that common and frequently unrecognized daytime sleepiness, related perhaps in some but not all cases to SDB, could underlie a sizeable portion of aggressive behaviors within urban public schools.
If sleepiness does contribute to aggressive behavior, then calculation of the population attributable risk percentage from our data suggests that 39.5% of conduct problems in the population we studied could be ameliorated by eliminating sleepiness. The latter proportion is somewhat higher than the population attributable risk proportion that can be calculated from a previous study that used the same 4-item sleepiness scale (29%; 41
), but the current study targeted exclusively children from an urban school system rather than a more mixed sample from pediatric clinics. Lower socioeconomic status and lower maternal educational level are both associated with poor sleep hygiene in children42
, and more than half (58%) of children in the present sample received school lunch assistance, which suggests lower socioeconomic status.
In our study, conduct problems and discipline referrals were associated with sleepiness even after adjustment for snoring and other confounders. The possibility that sleepiness may provide a mechanistic link between a nocturnal sleep disorder and daytime aggression is also supported by previous observations. Slowing of the EEG, which could reflect sleepiness, has been noted in aggressive children.43
Interestingly, longitudinal studies have suggested that EEG slowing may predict future criminality.44
Inadequate sleep in children, whether due to poor sleep hygiene, sleep restriction, or an underlying sleep disorder, is associated with a wide range of behavioral, cognitive, and mood impairments45
. Many young children in urban settings do not obtain enough sleep, probably for a variety of reasons that can include family schedules, chaotic living arrangements, nocturnal use of electronics in the bedroom, or after-school activities46
. If sleepiness does facilitate aggressive behavior, impairment of pre-frontal cortical function is likely the reason. The prefrontal cortex is the main generator of slow EEG waveforms and this brain region is among the most sensitive to sleep disruption.18
It plays a critical role in emotional control, decision making, and social behavior. Impairment of any of these functions could promote aggression.47
Neuropsychological studies of adolescents and adults indicate that aggressive behavior is associated with impairment in executive function.48
Children subjected to sleep deprivation show deficiencies in executive functioning, regulation of impulsivity, and emotional control.47, 49
Insufficient or short sleep may play a role in ADHD.50, 51
A modest but chronic reduction by 1 hour of sleep in early childhood is associated with worse cognitive performance at school entry, and higher hyperactivity scores despite improved and stable sleep duration between the ages of 3–6 years.52
A critical window during development may create vulnerability to lack of sleep, with detrimental consequences even if sleep duration subsequently improves.
Anatomical and physiological alterations have also been reported in aggressive individuals. Lesions of prefrontal cortical areas can disinhibit aggressive behaviors53
and individuals with frontal lobe damage sometimes use physical intimidation and threatening behaviors in conflict situations.54
Reductions in prefrontal grey matter have been reported in people with antisocial behavior and borderline personality disorder.55
Functional neuroimaging suggests deficient prefrontal activity in both sleep-deprived and aggressive individuals.56, 57
Furthermore, aggressive children display altered levels of autonomic responses. Low resting heart rate is a robust finding in aggressive children,58, 59
who also have high levels of autonomic reactivity to stressful situations.60
Accumulating evidence suggests that hyperactive children are sleepier than their peers.38, 61
Use of stimulant medications improves behavior; the paradoxical effect of stimulants also supports the hypothesis that underlying sleepiness could play a critical role in behavioral manifestations. Similarly, stimulants may help rather than exacerbate conduct disorder in children.62
Evidence is growing to support the idea that SDB may cause or contribute to disruptive behavior disorders. Hyperactive and inattentive behavior is robustly associated with SDB symptoms15, 17, 38
and follows SDB symptoms in longitudinal studies.63
Follow-up assessments after treatment for SDB have documented improvement in disruptive behaviors.25
A randomized-controlled clinical trial is now underway to determine whether expedited adenotonsillectomy for SDB, in comparison to watchful waiting, improves attention and other neurobehavioral outcomes at 6 months. Interestingly, several studies suggest that hyperactive behavior in childhood may be a precursor of later aggression.64, 65
A limitation of our study was the inability to recruit more than 30% of students. This level of participation is significantly higher than a previous study in the same school district40
and is commendable for a public school survey in an urban area. In comparison to other published mailed survey studies requiring active consent in urban settings, our participation was similar or better66, 67
. Although selection bias may nonetheless have influenced our findings, associations between variables, as we report, should be less vulnerable to such biases than raw prevalence estimates. Other limitations include that a questionnaire, though previously validated against polysomnography, was used to assess SDB risk. No other studies to date have applied full polysomnography in children with conduct disorder. The population attributable risk percentage noted above is presented as an approximation only, as the present study was not a true epidemiological sample. Additional limitations include the inconsistency between parent and teacher reports of behaviors. The small number of children who were reported to bully or have conduct problems by both parents and
teachers made it impossible to use dually confirmed definitions for analysis. However, these disparities were not unexpected. Multiple studies have found inconsistent relationships using teacher reports of behavior22, 68
but robust associations using parental reports.69
Finally, sleepiness can occur for many reasons, and the present study was designed to assess SDB risk using a composite of snoring and sleepiness scores, rather than all possible causes of sleepiness. Actigraphy or other objective measures of sleep quantity were not used.
Nonetheless, our data now raise the possibility that sleepiness, whether or not caused by SDB, could play an important role in aggressive behavior among schoolchildren.. Given the high prevalence of aggressive, bullying, and disruptive behaviors in schools, and long-lasting consequences for both perpetrators and victims, identification of modifiable biological contributors should be a high priority. Our findings do not prove a cause-and-effect relationship, but raise the possibility that addressing the underpinnings of childhood sleepiness may offer a largely untapped opportunity to reduce the common problem of aggressive behavior in schoolchildren.