The relationship between sleep difficulties and externalizing and internalizing problems in children and adolescents with mental illness.

Sleep difficulties are presumably a transdiagnostic factor in the complex aetiology of psychiatric disorders in youth. This study assessed the prevalence of sleep difficulties in children and adolescents seeking specialized psychiatric care, examined the relationships of internalizing and externalizing problems, and considered the moderating role of sex and age on these relationships. Parent-reported data on difficulties initiating sleep, difficulties maintaining sleep, early morning awakenings and daytime fatigue from a large sample of children and adolescents referred for specialized psychiatric care (n = 4638; < 18 years) were used to estimate prevalence rates. To examine associations between these sleep difficulties and internalizing/externalizing problems, multiple linear regression analyses were conducted on available data (n = 3768) stratified in three age groups (1.5-5 years; 6-11 years; 12-18 years). Overall prevalence, i.e. at least one sleep difficulty was reported to be often or always present, was 65%. Difficulties initiating sleep occurred the most, closely followed by daytime fatigue. In all age groups, sleep difficulties were positively related to internalizing and externalizing problems. In young children and school-age children, age moderated the interaction between sleep difficulties and internalizing problems. To conclude, prevalence rates of sleep difficulties in children with mental illness appear higher than it has been reported in the general youth population, especially difficulties initiating sleep and daytime fatigue. We observed that the associations between internalizing problems and sleep difficulties in young children and school-age children seemed to be amplified with age, suggesting a negative, bidirectional, spiral in development.