Abstract
Purpose: The negative correlates of childhood sleep difficulties have been well documented. However, the effects of such problems on child development are still poorly understood. The aim of the current study was to assess the relationship between sleep consolidation (sleep maturity), both concurrently and longitudinally from infancy, with behaviour, cognition and sensory processing of toddlers.
Methods: Dunedin children (n=159; 49% male, 51% females) were recruited from an existing longitudinal study (POI Study) as they turned 30 months of age ± 0.6 months. Sleep patterns were reported by parents at 30 months of age using a sleep questionnaire and daytime behavioural functioning was rated using the Behaviour Assessment System for Children, 2nd Edition (BASC-2). Sensory processing was rated by parents using the Sensory Processing Measure – Preschool (SPM-P). The cognitive development of the children was assessed using the Wechsler Preschool and Primary Scale of Intelligence, 3rd Edition (WPPSI-III). Sleep variables included sleep duration, night waking, longest sleep period at night, nap duration and nap frequency. Developmental trajectories were determined for each sleep variable using data collected over the first 2 years of life. Based on the resulting trajectories, children’s sleep development was coded as less consolidated or more consolidated for each sleep variable. Using hierarchical multiple regression, the association of sleep consolidation with behavioural and cognition outcomes, concurrently at 30 months of age, was assessed. Next, the sleep trajectory groups were used to measure the predictive capacity of sleep consolidation variables on behavioural and cognitive outcomes at 30 months of age, over and above concurrent sleep behaviour. Lastly, the relationship between sleep consolidation and sensory processing was measured concurrently at 30 months of age and longitudinally, measuring the predictive capacity of sleep variables on sensory processing outcomes at 30 months of age, over and above concurrent sleep behaviour.
Results: On average, children at 30 months of age slept for 11 hours ± 11 minutes, and longer sleep durations at night were associated with less frequent (r=-0.290, p<0.001) and shorter naps (r=-0.285, p<0.001). Concurrently, shorter sleep durations were correlated with higher ratings of hyperactivity (p=0.03) on the BASC-2, whilst more frequent night waking was associated with higher scores for somatisation (p<0.0001). Lower scores for performance
IQ, measured using the WPPSI-III, were associated with both longer nap duration (p=0.05) and more frequent napping (p=0.009). Lower social skills ratings on the BASC-2 were also predicted by longer nap duration (p<0.0001) and more frequent napping (p=0.008). Longitudinally, children who slept for consistently shorter durations over the first two years of their life were more likely to obtain higher ratings on the BASC-2 at 30 months for aggression (p=0.026) adding 3.9% new variance, bullying (p=0.001) adding 7.9% new variance, and developmental social disorders (p=0.011), adding 5.0% new variance, over and above their concurrent sleep patterns. Children with consistently shorter longest sleep period (LSP) scores over the first two years of life were more likely to have higher scores for aggression (p=0.031) at 30 months of age, adding 3.7% new variance above concurrent sleep patterns. When examining the concurrent relationship between sleep and sensory processing ratings on the SPM-P, children who slept for shorter durations were more likely to score higher (worse) for the total sensory processing (p=0.01), adding 5% new variance. Children who slept for shorter durations concurrently were more likely to score higher (worse) for social participation (p=0.006) on the SPM-P, adding 6% new variance. Longer nap durations concurrently predicted poorer scores for planning and ideas (Praxis) (p = 0.03), adding 6% new variance. Longitudinally, children with consistently shorter sleep durations over the first 2 years of life were more likely to obtain higher scores (worse) for social participation (p= 0.002) on the SMP-P, adding 9% new variance, over and above concurrent sleep behaviour.
Conclusions: The results of the research set out in this thesis support the hypothesis that sleep that is less consolidated is concurrently related to less-optimal daytime functioning in the area of behaviour, cognition and sensory processing in toddlers. In addition, less mature sleep persisting over the first two years of life predicts poorer behavioural and sensory processing scores at 30 months of age. These findings suggest that sleep problems in infancy and early childhood should be treated as a genuine health consideration to prevent possible adverse effects on development.