Attention-deficit/hyperactivity disorder (ADHD) is characterized by impulsivity/hyperactivity and inattention, with symptom onset before 7
years of age and impaired functioning in two or more environmental settings
]. ADHD is estimated to occur in 3–7.5% of school-aged children, making it one of the most prevalent child psychiatric conditions. Moreover, 50% of children diagnosed with ADHD also suffer from impairment as young adults
]. Parental reports indicate a 2- to 3-fold higher prevalence of sleep problems in children with ADHD compared to normal controls
], including increased bedtime resistance
], delayed sleep onset
], frequent waking in the night
], frequent motor movements during sleep
], and morning/daytime fatigue
]. As well, approximately one-third of medication-free children with ADHD experience chronic sleep-onset insomnia (SOI)
Sleep problems presenting in a child with ADHD may stress both the child and family. Furthermore, sleep disturbances can cause excessive daytime fatigue and interfere with several aspects of an individual’s daytime functioning, including mood, attention span, and behavior
], which are critical to school or work performance. Accurate diagnosis and effective management of sleep problems are key to significantly improving the quality-of-life of both children with ADHD and their family members.
Despite the clinical and scientific relevance of sleep problems to the understanding and management of ADHD, the etiologies of such sleep issues remain unclear. This is particularly important for an accurate evaluation of possible causes related to parental descriptions of sleep onset problems in children with ADHD and in choosing the most effective intervention.
Amongst the potential etiologies for sleep onset problems, both behavioral and biological explanations have been advanced within the current literature. The behavioral model posits that prolonged sleep onset and delayed bedtime in children with ADHD are a result of behavioral problems, leading to increased resistance at bedtime and difficulty in settling down in the evening. According to this model, an intervention should target the behavioral problems that lead to delayed bedtime and sleep deprivation in children with ADHD. In contrast, the circadian model suggests that children with ADHD are averse to bedtime because they are sent to bed before feeling the need to sleep. In particular, it is suggested that a delay in the endogenous circadian rhythm delays sleep and waking times
]. Such discord may lead parents to attribute child conduct to the presence of a disruptive behavioral disorder, such as ADHD, when the true problem may be an underlying circadian disorder causing both bedtime refusal
] and increased daytime fatigue
]. The circadian model suggests that interventions should aim to synchronize the circadian clock of children presenting with ADHD to the environmental light–dark cycle in order to effectively treat delayed sleep onset and delayed bedtimes. The recommended interventions have included melatonin administration and light therapy to reset the circadian timing system
]. The diverse views summarized above suggest different interventional strategies, depending on the mechanism that is at play. Thus, it is of critical importance to identify the etiology.
In addition, it is also unclear if such problems are unique to children with ADHD. It has been suggested that children with ADHD may have a deficit in arousal regulation and further factors associated with sleep or bedtime behavior might, thus, be specific to this population. However, to date, this hypothesis has not been tested. As such, the objectives of this study were two-fold: The first goal was to determine the relative contributions of circadian preferences and behavioral problems in relation to sleep onset issues, specifically – sleep onset insomnia and bedtime resistance – experienced by children with ADHD and in controls. Since inconsistencies in the detection of sleep problems using PSG and parental reports have been documented, we examined and compared both sources of information. The second objective of this study was to test for a moderation effect of diagnosis (ADHD vs. control) on the impact of circadian preferences and externalizing problems on sleep problems. We hypothesized that 1) stronger evening circadian preferences would be associated with longer SOI in both children with ADHD and controls; 2) a greater level of externalizing problems would be associated with elevated bedtime resistance in both groups; and, 3) that a stronger impact of circadian evening preferences and behavioral problems on bedtime behavior would be evident in the ADHD group compared to controls.