Seasonal Variation In Objectively Measured Physical Activity, Sedentary Time, And Sleep Duration Among Children

Purpose Understanding fluctuations in lifestyle indicators is important to identify relevant time periods to intervene in order to promote a healthy lifestyle; however, objective assessment of multiple lifestyle indicators has never been done using a repeated-measures design. The primary aim was, therefore, to examine between-season and within-week variation in physical activity, sedentary behaviour and sleep duration among 8-11 year-old children.

Methods A total of 1021 children from nine Danish schools were invited to participate and 834 accepted. An ActiGraphTM accelerometer (GT3X+ or GT3X) was worn for 7 days and 8 nights on the waist during autumn, winter and spring, from which physical activity, sedentary time and sleep duration were measured. Physical activity and sedentary time were obtained between 6 am and midnight. To remove non-wear time and nocturnal activity during early morning and late evening, ≥15 minutes of consecutive zeros and consecutive wear time of less than 60 minutes was disregarded before analysis. ≥10 hours of measured monitor wear time was considered a valid day. Vertical axis and epoch length of 1 min was used. Sedentary time was defined as ≤100 cpm and moderate-to-vigorous physical activity (MVPA) as ≥2296 cpm. To estimate sleep duration from the accelerometer, self-reported bedtimes and waking times were used as the possible window of sleep and scored in ActiLife 6. A minimum of 3 weekdays and 1 weekday was considered necessary; hence 730 children were included in the current analytical sample. The study is part of the OPUS (Optimal well-being, development and health for Danish children through a healthy New Nordic Diet) School Meal Study*.

Results Mean MVPA, sedentary time and sleep duration were 0:50, 7:55 and 9:10 h:mm/day, respectively. The children spent 30% more time in MVPA during spring compared to winter and 49% more time during weekdays compared to weekends (P<0.001). Sedentary time was 5% higher during winter compared to spring and during weekends compared to weekdays (P<0.001). Sleep duration was 15 min shorter during spring compared to autumn, with 7 min less sleep during weekends (P<0.001). Interclass correlation coefficients between seasons ranged from 0.47-0.64, leaving 59-78% to seasonal variation.

Conclusions Collectively, the lifestyle of children in this cohort was relatively healthier during spring and weekdays. The considerable intra-individual variation when measured across three different seasons suggests that a single measurement taken at one point in time may not adequately characterize children’s habitual sleep and activity. *Supported by a grant from the Nordea Foundation.