Chronotype and time-of-day effects on spatial working memory in preschool children.

STUDY OBJECTIVES: Spatial working memory (SWM) capacity subserves complex cognitive functions, yet it is unclear whether individual diurnal preferences and time-of-day influence SWM in preschool children. The main and interaction effects of chronotype and time-of-day on SWM and SWM differences in preschoolers with different chronotypes within each time-of-day group will be examined. METHODS: We studied a subset of typically developing 4.5-year-olds taking part in a birth cohort study (n = 359). The Children's Chronotype Questionnaire categorized children into morning-, intermediate-, and evening-types. Using a computerized neuropsychological test (Cambridge Neuropsychological Test Automated Battery), SWM was determined from the total number of between-search errors (ie, between search-total errors) and Strategy scores. Higher between search-total errors or lower Strategy scores indicated worse SWM. Time-of-day was categorized into late morning (10:00 am to 11:59 am), afternoon (12:00 pm to 3:59 pm), and late afternoon (4:00 pm to 6:30 pm). In a subsample (n = 199), caregiver-reported chronotype was validated using actigraphy-measured sleep midpoint. RESULTS: After controlling for ethnicity, no significant main and interaction effects of chronotype and time-of-day on between search-total errors and Strategy scores were seen (all P > .05). However, evening-types outperformed morning-types (ie, lower mean between search-total errors) in the late afternoon (P = .013) but not in the late morning and afternoon (all P > .05). Actigraphy data in the subsample confirmed that evening-types had later sleep midpoints during weekdays and weekends (P < .001). CONCLUSIONS: Since evening-type preschoolers had better SWM in the late afternoon compared to morning-type preschoolers, this gives insights into optimal learning opportunities in early childhood education. CITATION: Abdul Jafar NK, Tham EKH, Eng DZH, et al. Chronotype and time-of-day effects on spatial working memory in preschool children. J Clin Sleep Med. 2023;19(10):1717-1726.

Preconception sleep quality moderates the association between preconception hair cortisol levels and mental health in pregnant women.

BACKGROUND: Poor sleep quality may elevate cortisol levels and affect prenatal mental health through altered HPA axis functioning. This study aims to examine whether subjective sleep quality during preconception moderates the association between preconception hair cortisol levels and mental health from preconception to pregnancy trimesters. METHODS: Women from a prospective cohort study completed the Pittsburgh Sleep Quality Index (PSQI), the Edinburgh Postnatal Depression Scale (EPDS), and the State-Trait Anxiety Inventory (STAI) questionnaires during preconception (T0) and at each pregnancy trimesters (T1, T2, and T3). We analyzed 266 of these women who conceived and had fully completed measures at preconception for hair cortisol, sleep quality and either EPDS or STAI-state. Changes in EPDS and STAI-state scores were derived (i.e., T1-T0, T2-T0, T3-T0). Johnson-Neyman technique identified PSQI scores with significant moderation of cortisol on mental health. RESULTS: After adjusting for potential covariates, there was a significant positive correlation between preconception hair cortisol levels and depressive symptom at the second trimester (rs (144) = 0.22, p = 0.008), but not the first and third trimesters (all ps > 0.05). The positive association between preconception hair cortisol and change in depressive symptoms between third trimester and preconception was significant only among women with poor preconception sleep quality (PSQI ≥ 7). LIMITATIONS: Sleep quality and prenatal mood were derived from self-reported questionnaires, which may be more susceptible to bias. CONCLUSIONS: The positive association between preconception hair cortisol and change in prenatal depressive symptoms is significant among women who reported poor sleep quality during preconception. Improving preconception sleep quality can potentially mitigate the association between preconception hair cortisol and depressive symptoms during pregnancy.

Association between breastfeeding and sleep patterns in infants and preschool children.

BACKGROUND: Although most studies have reported unfavorable short-term effects of breastfeeding on early-childhood sleep-wake behaviors that potentially attenuate over time, findings have remained inconsistent. OBJECTIVES: We assessed associations of breastfeeding with longitudinal day-, night-, and total-sleep trajectories and with sleep-wake behaviors in healthy infants and preschoolers. METHODS: Caregivers of naturally conceived, term, singleton infants (n = 654) completed the Brief Infant Sleep Questionnaire (3, 6, 9, 12, 18, and 24 mo) and/or Children's Sleep Habits Questionnaire (54 mo), and provided information on their infants' breastfeeding status at 3 mo. Trajectory analyses derived 4 day- (n = 243), 3 night- (n = 248), and/or 4 total- (n = 241) sleep trajectories, each differing in length of sleep duration (short/moderate/long) and variability (variable/consistent). Sleep-wake behaviors from 3 to 24 mo (day/night/total-sleep durations and duration/number of night awakenings) were also assessed for associations with breastfeeding. RESULTS: After adjusting for potential covariates, formula-fed infants, relative to fully breastfed (predominant or exclusive) infants, were significantly less likely to exhibit moderate (OR: 0.28; 95% CI: 0.11, 0.70) and long consistent (OR: 0.18; 95% CI: 0.07, 0.50) night-sleep trajectories and less likely to exhibit moderate (OR: 0.21; 95% CI: 0.07, 0.61) and long consistent (OR: 0.12; 95% CI: 0.04, 0.38) and long variable (OR: 0.16; 95% CI: 0.05, 0.56) total-sleep trajectories, instead of short variable night- and total-sleep trajectories. Partially breastfed infants did not differ from fully breastfed infants for both night- and total-sleep trajectories. No significant differences were found between all groups for day-sleep trajectories. Fully breastfed infants had longer night- (6, 9, 12, and 24 mo) and total- (3 and 12 mo) sleep durations than formula-fed infants, albeit a greater number of night awakenings (from 6 to 12 mo). CONCLUSIONS: Despite more night awakenings, fully breastfed infants have overall longer night- and total-sleep durations (sleep trajectories) than formula-fed infants.