Active travel and children’s BMI z-score: a study within a cluster randomized trial

Background
Active travel has been associated with increased physical activity engagement and better fitness. However, there is limited evidence regarding the impact of active travel on weight management in children.

Purpose
This study assessed whether active travel is associated with changes in body mass index (BMI) z-score in children over 12 months.

Methods
This study is part of a large 3-arm cluster randomised trial (MapMe2). Height and body mass measurements for 619 children in Reception (4-5 years) and Year 6 (10-11 years) were collected at baseline and followed up after 12 months. Parents reported how their children travelled to school via paper or online questionnaire. Responses were categorised as ‘active’ (bike, walk, scooter) and ‘passive’ (car, bus, metro). We assessed physical activity using triaxial ActiGraph wGT3X-BT accelerometers. We conducted a subgroup analysis for each school year. Using mixed effects models, we examined the association between active/passive travel groups, physical activity, and change in BMI z-score.

Results
For children in Reception, greater sedentary time was associated with a significantly lower BMI z-score (β = -0.018, 95% CI: -0.033 to -0.002, p = 0.026). Year 6 children who engaged in more minutes of moderate-to-vigorous physical activity (MVPA) had a significant decrease in BMI z-score (β = -0.010, 95% CI: -0.016 to -0.003, p = 0.006). Active travel was not significantly associated with BMI z-score in both groups.

Conclusions
No direct association between active travel and BMI z-score was observed in Reception or Year 6 children. Higher MVPA in Year 6 was associated with lower BMI z-score. While active travel alone may not impact BMI z-scores, increasing MVPA could benefit weight management, especially in older children.

Practical Implications
Active travel may support weight management indirectly through increased MVPA. Further research is needed to clarify this relationship.

Funding
NIHR Public Health Research Programme (NIHR127745).