Humans spend approximately one-third of their lives sleeping, with children sleeping more than adults. A large scientific literature repeatedly attests to the association between a range of sleep qualities – including the amount of time – and aspects of child development. And yet, studies that more directly estimate the causal effects of time sleeping on various health, cognitive and non-cognitive outcomes in children and adolescents are scant. This paper examines the causal impact of sleep duration on health and development of children and adolescents.
Using over 50 thousand time use diaries from two cohorts of Australian children spanning over 16 years in the Longitudinal Study of Australian Children (LSAC) survey, we first document that, on days with longer daylight duration, children sleep significantly less, partly by going to sleep later and waking up earlier. On such days, they also reduce the time allocated to personal care or media activities and increase the time to school or physical activities. We present new evidence indicating that the effects of daily daylight duration on sleep duration are greater for females, older individuals, children of employed mothers or on weekends/holidays.
We then exploit variations in local daily daylight duration measured on pre-determined diary dates across the same individuals through time to draw causal estimates of sleep duration on a comprehensive set of child development indicators. We find that sleeping longer improves selected general developmental and behavioural outcomes. Our results also reveal that sleeping more increases the probability of having excellent health or decreases the likelihood of having any ongoing condition. By contrast, sleeping longer statistically significantly increases BMI scores, mainly by increasing the risk of being overweight. Furthermore, the results show statistically insignificant or a relatively small positive impact of sleeping more on cognitive development. The findings presented in this paper highlight the importance of addressing potential endogeneity of sleep duration when quantifying its impact on child developmental outcomes. The findings of substantial health and development benefits of sleeping longer from this study reinforce the need to formulate policies to reduce sleep deprivation in young individuals, especially in females and adolescents who appear to benefit more. This paper also identifies potentially detrimental effects of sleeping longer on some developmental outcomes, including increased BMI and a higher risk of being overweight for males, and these side effects should be considered when designing such policies.