Pre-bedtime light, physical activity, and sleep in children with Autism Spectrum Disorder

Introduction: Children with Autism Spectrum Disorder (ASD) suffer from insomnia at much higher rates than typically developing (TD) peers. Research indicates that sleep problems in ASD may be due to hypersensitivities to stimuli and melatonin deficiencies. Behavioral treatments for insomnia in ASD often include sleep hygiene recommendations to avoid physical activity and light intensity within two hours of bedtime. However, despite these recommendations, research examining the relationship between physical activity and light intensity close to bedtime and sleep outcomes in TD and ASD is sparse. The current study examines associations between pre-bedtime light intensity exposure, physical activity, and sleep in children with ASD and in TD children. Methods: Children with ASD (n=28, Mage=8.4, SD=1.7) and 27 TD children (n=27, Mage=8.9, SD=1.8) who met DSM-5 criteria for insomnia disorder completed 14 concurrent days of sleep diaries with parental assistance and 14 days of wrist worn actigraphy. Sleep diaries and actigraphy obtained estimates of sleep onset latency (SOL), wake time after sleep onset (WASO), and total sleep time (TST) for each night, and actigraphy also obtained light intensity exposure and average physical activity in five timeframes prior to bedtime (0-30 minutes, 0-60 minutes, 0-120 minutes, 120-240 minutes, and 240-360 minutes). Multi-level models examined intra-individual and inter-individual associations between pre-bedtime physical activity, light intensity, and subjective/actigraphic sleep outcomes, as well as whether these associations differed between children with ASD and TD. Results: Greater light intensity was associated with longer subjective SOL (B=0.18, p=0.04, 120-240 mins, inter-individual), longer subjective WASO (B=0.05, p<0.001, 120-240 mins, intra-individual), and shorter subjective TST (B=-0.42, p=0.02, 120-240 mins, inter-individual) in TD but not ASD. Greater light intensity was associated with longer subjective SOL (B=0.08, p=0.05, 0-60 mins, intra-individual), and longer subjective TST (B=1.25, p=0.04, 0-120 mins, inter-individual) for ASD, but not TD. Greater light intensity was associated with longer actigraphic SOL (B=0.07, p=0.05, 0-60 mins, inter-individual) in ASD, but not TD, and longer actigraphic WASO (B=0.02, p<0.01, 120-240 mins, intra-individual) in TD, but not ASD. Greater physical activity was associated with longer subjective TST (B=0.30, p=0.01, 0-30 mins, inter-individual; B=0.36, p<0.01, 0-60 mins, inter-individual; B=0.26, p=0.02, 0-120 mins, inter-individual) and shorter actigraphic SOL (B=-0.05, p=0.01, 240-360 mins, intra-individual) in both ASD and TD. Conclusion: Results do not support sleep hygiene recommendations for avoidance of pre-bedtime physical activity, but they generally support avoidance of pre-bedtime light intensity. We speculate that pre-bedtime light intensity exposure may interfere with sleep outcomes through impeding melatonin secretion. Further, our results do not support the mechanism that hypersensitivities to light or physical activity are primarily responsible for insomnia in ASD relative to TD, since both ASD and TD showed similar associations between light, physical activity, and sleep outcomes (i.e., greater pre-bedtime light associated with worse sleep and greater pre-bedtime activity associated with better sleep). Future research should examine the relationship between pre-bedtime light exposure and melatonin production in ASD and explore whether sleep hygiene recommendations to avoid pre-bedtime physical activity are warranted in ASD and TD.