Associations of chronotype with daytime functioning and obesity in elementary school children.

OBJECTIVE: Evidence linking chronotype to daytime functioning and obesity in elementary school-aged children remains limited. This study examined the associations between chronotype and sleepiness, emotional/behavioral problems, obesity, and morning vigilant attention. METHODS: Children from six elementary schools in Tokyo, Japan, were recruited. Chronotype was indexed by the sleep-corrected midpoint of sleep on free days (MSFsc). Outcomes included obesity, child-reported morning sleepiness, parent-reported daytime sleepiness, and emotional/behavioral problems assessed using the Strengths and Difficulties Questionnaire. Morning vigilant attention was assessed using a 3-min Psychomotor Vigilance Test (PVT) on two consecutive mornings. Non-PVT outcomes were analyzed using generalized linear and logistic regression models, and repeated PVT measures were analyzed using mixed-effects models. RESULTS: The sample included 1893 children (mean age ± SD, 9.0 ± 1.7 years; age range, 6-12 years; 51.2% boys). Each 1-h delay in MSFsc was associated with a higher BMI z-score (β = 0.099, q = 0.01), greater morning sleepiness (β = 0.268, q < 0.001), greater daytime sleepiness (β = 0.073, q < 0.001), and more emotional/behavioral problems (q < 0.05). Compared with intermediate chronotype, late chronotype showed higher estimated odds of obesity (OR = 1.92, q = 0.05), whereas early chronotype showed faster response speed (β = 0.068, p = 0.04) and fewer lapses (β = -0.145, p = 0.02) in PVT analyses (n = 1580). CONCLUSION: Later chronotype was associated with greater sleepiness, more emotional/behavioral problems, and higher BMI z-scores. Early chronotype was associated with better morning vigilant attention than intermediate chronotype.