Research Study Abstract

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

  • Presented on June 17, 2013

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.