Correlates of nocturnal sleep duration, nocturnal sleep variability, and nocturnal sleep problems in toddlers: results from the GET UP! Study

Objective: To explore the correlates of nocturnal sleep duration, nocturnal sleep variability, and nocturnal sleep problems in a sample of Australian toddlers. Methods: Participants were 173 toddlers (average age 19.7 ± 4.1 months) from the GET UP! Study. Nocturnal sleep duration, nocturnal sleep variability, nap(s) and physical activity were measured using 24-h accelerometry (Actigraph GT3X+) over seven consecutive days. Nocturnal sleep problems were assessed using the Tayside Children's Sleep Questionnaire. Screen time was reported by the parents. Logistic regression models were used to examine the associations between potential correlates (ie, age, sex, socio-economic status, weight status, physical activity, screen time, nap(s), bedtimes, and wake-up times) and nocturnal sleep characteristics. Results: Older children were more likely to have greater sleep variability (OR: 1.97; 95% CI: 1.08- 3.61). Less physical activity (OR: 2.38; 95% CI: 1.27- 4.45), shorter nap(s) (OR: 2.42, 95% CI: 1.29-4.55), and later wake-up times (OR: 4.42; 95% CI: 2.32-8.42) were associated with higher odds of having longer nocturnal sleep duration. Late bedtimes were associated with shorter nocturnal sleep duration (OR: 0.09; 95% CI: 0.04-0.18) and with greater nocturnal sleep variability (OR: 1.97; 95% CI: 1.06-3.68). None of the potential correlates were associated with nocturnal sleep problems. Conclusion: The present study identifies several correlates of nocturnal sleep duration (total physical activity, nap(s), bedtime, and wake-up time) and nocturnal sleep variability (age and bedtime), whereas no correlates were identified for nocturnal sleep problems. The association between late bedtimes and shorter nocturnal sleep duration and greater nocturnal variability suggests that these may be modifiable targets for future sleep interventions in early childhood. Trial registration: Australian New Zealand Clinical Trials Registry: ACTRN12616000471482, 11/04/2016, retrospectively registered.