Sleep Problems in Autism Spectrum Disorders: The Influence of Anxiety, Restricted and Repetitive Behaviours and Intolerance of Uncertainty

Background:  Sleep problems are one of the most common comorbidities experienced by individuals with ASD. While sleep problems have been well characterized in children with ASD less is known about the types of sleep disturbances experienced by adults with ASD. Further, the aetiology of the sleep disturbances is relatively unknown. It has been suggested that the inherent anxiety experienced by those with ASD may predispose them to experience sleep problems. In addition, core behaviours associated with ASD such as restricted and repetitive behaviours and an intolerance for uncertainty may also lead to delayed sleep onset and reduced total sleep time. 

Objectives:  The aim of this study was to investigate the relationships between sleep disturbance and symptoms of anxiety, restricted and repetitive behaviours (RRBs), and intolerance of uncertainty in adults with ASD and no intellectual impairment compared to age-, sex-, and IQ-matched NT adults.

Methods:  Thirty adults with ASD and 30 NT adults participated in the study. Participants completed an online questionnaire battery that contained the Autism Quotient, the Pittsburgh Sleep Quality Index (PSQI), the State Trait Anxiety Inventory (STAI), the Restricted Behaviour Questionnaire-2 Adult (RBQ-2A), and the Intolerance of Uncertainty Scale (IUS). 

Results:  Adults with ASD had higher total PSQI scores as well as higher scores on the sleep quality, sleep latency, sleep disturbance, and daytime dysfunction due to sleepiness subscales of the PSQI; effect sizes were moderate to large. Adults with ASD had significantly higher total and subscale scores on the STAI, RRB-2A, and IUS; all effect sizes were large. In assessing the relationship between sleep and the other variables, PSQI total scores were significantly correlated with both state (r = .63) and trait (r = .52) anxiety and the rigidity/adherence to routine subscale of the RBQ-2A and the uncertainty paralysis (r = .46) of the IUS. There were no significant correlations between PSQI scores and any of the other variables in the NT group. Hierarchical regression was used to determine predictors of PSQI scores in the ASD group; state anxiety, rigidity/adherence to routine and uncertainty paralysis were entered into the regression. The model accounted for 37.5% of the variance in PSQI scores, with only state anxiety being a unique predictor. 

Conclusions:  This is one of the first studies to assess the relationship between sleep, anxiety, RRBs, and intolerance of uncertainty in adults with ASD. As expected adults with ASD had higher scores on all questionnaire measures and subscales, confirming that atypical sleep persists from childhood into adulthood in ASD.  While RRBs and intolerance of uncertainty were related to sleep problems in the ASD group, only state anxiety was a unique predictor of PSQI scores. Treatments that aim to target anxiety, particularly around the onset of sleep, may improve sleep. Further, this may have a direct effect on RRBs and the experience of intolerance of uncertainty.