Objective: This study aimed to explore sleep duration in young Australians on different types of days across weight classes.
Methods: Use of time and anthropometric data were collected on 8,866 nights from 3,884 9–18 year old Australians. The association between sleep duration and weight status was examined using factorial ANOVA for four day types: S-S (to bed and waking on school days); S-NS (to bed on school day and waking on non-school day); NS-NS (to bed and waking on non-school days); NS-S (to bed on non-school day and waking on school day).
Results: Sleep duration varied with weight status when all day types were considered together (p=0.0012). Obese adolescents slept less than normal and underweight adolescents. However, the relationship varied for different day types; with the strongest relationship for NS-S days (on which obese children slept 65 min less than very underweight children, p<0.0001).
Conclusions: The association between weight status and sleep duration showed consistent gradients across weight categories, but only for certain day types.
Implications: These patterns cast light on the direction of causation in the obesity-sleep duration relationship. Findings suggest that short sleep duration contributes to obesity, or that a third unidentified factor has an impact on both.