The Longitudinal Influence of Neighbourhood Green Space on Children’s Physical Activity, Screen Time, and Body Mass Index

Abstract

Purpose: It is often hypothesised that green space (e.g., parks) may influence children’s weight status; however, evidence remains limited and largely cross-sectional. Further, hypothesised behavioural mechanisms for this effect, such as physical activity, are poorly understood. The purpose of this study was to investigate associations between neighbourhood green space and children’s BMI trajectories over early childhood, and to investigate longitudinal associations with physical activity and screen time. Methods: Data came from the Longitudinal Study of Australian Children (LSAC) – an Australian Government project that collects data from a nationally representative sample of children. Participants (n=4,423) had their BMI objectively measured, and their physical activity and screen time reported by the parents and child every 2 years between 2006 (age=6-7) and 2012 (age=12-13). Green space data were derived from Australian Bureau of Statistics mesh blocks – which classify small land parcels according to their primary use. Participants were assigned an objective measure of green space for their statistical area level 2, the smallest area measure available in the LSAC. Gender-stratified multilevel linear regressions were used to investigate associations between green space and the outcome measures. Growth curve models were used to examine changes in trajectories. The child’s family income, maternal education level, Australian indigenous status, and language spoken at home were included as socio-economic controls. Results: After adjustment for socio-economic status, a significant interaction between age and green space on BMI was noted for boys (p=0.009), but not girls (p=0.056), such that the influence of green space becomes more pronounced as children grow older. For boys, each 10% difference in green space was associated with a: (i) 7.3% increase in the odds of choosing physical active pastimes; (ii) 2.4min reduction in weekend television viewing; and (iii) 8.4% increase in the odds of meeting physical activity guidelines on weekends. There were no significant results on girls’ physical activity or screen time. Conclusions: Green space appears beneficial to boys’ BMI as they grow older, but not girls’. Increased physical activity and decreased screen time may explain this effect. Modest differences in green space elicited a response, suggesting small changes to the environment may be beneficial.