Exploring the associations between physical activity, sleep, sedentary behaviour, and mental health in young German...

Early childhood is a period of rapid development; research shows that the formation of healthy habits during this period can result in higher physical fitness levels and better sleep, but also long-term improved mental health and wellbeing. Despite structures supporting physical activity (PA) and related behaviours, many German children under 6 years do not achieve the recommended levels of PA, sedentary behaviour (SED), and sleep; this in turn can hinder the formation healthy lifestyle habits in the early years, and also lead to long-term poor mental health, later in life. Thus, this study aimed to explore the associations between device-based measured PA with nighttime sleep, SED, and mental health in German children under six years of age.

PA, sleep, and SED were assessed at baseline and 1-year follow-up using wrist-worn GENEActiv accelerometers sampled at 100 Hz. The R-package GGIR (version 3.1.1) was used to derive light-intensity PA (LPA), moderate-to-vigorous-intensity PA (MVPA), total PA (TPA), inactivity (proxy for SED), total night sleep time (TST), and sleep efficiency (SE). Parents answered on children's mental health using the Strengths and Difficulties Questionnaire (SDQ). Linear mixed models, were used to estimate cross-sectional associations from repeated measures of PA intensities with sleep, SED, and mental health, adjusting for age and sex of the child, parental education, migration background, urbanity, and household income.

We investigated 212 children aged 2-6 years (51% female at baseline, 5.2% overweight or obese). At baseline, children spent on average 418.7 min/day inactive, 252.6 min/day in MVPA, and 480 min/day asleep, with a SE of 80%. The results indicated relevant associations of LPA, MVPA, or TPA with SED, SE, or TST, but no association of PA variables and SDQ.

Given the rapid developmental changes in early childhood, it is essential to track 24-hour movement behaviors, and mental health over time using device-based measures to better inform strategies that promote lifelong physical and mental wellbeing. Future multi-component interventions should be explored to determine potential synergistic benefits for mental health.