Within- and between-person associations between 24-hr movement behaviors and irritability in early childhood.

This study examined associations between 24-hr movement behaviors and irritability in young children.Parents of 1,266 children (52% boys) from the Longitudinal Study of Australian Children completed 24-hr time-use diaries at ages 2 and 4, reporting sleep, physical activity, screen time, nonscreen sedentary behavior, and irritability.Bayesian multilevel compositional data analysis and isotemporal substitution models assessed within-and between-person effects.Children who typically spent more time in physical activity were irritable significantly less often, while more screen time was linked to greater time being irritable.On days when children were more active than usual, irritability was less common.Substituting screen or sedentary time with physical activity was associated with reduced irritability, suggesting that promoting physical activity may support early childhood mental health. Public Significance StatementThis study found a link between how young children spent their time throughout the day and time spent being irritable.Substituting sedentary time with physical activity was related to better outcomes both at the stable between-person level and dynamic daily level.Intervening to promote healthier 24-hr time-use behaviors could be a viable approach to reducing irritability in the early years.