The impact of long-term school-based physical activity interventions on body mass index of primary school children - a meta-analysis of randomized controlled trials.

BACKGROUND Physical activity (PA) intervention is a commonly recommended strategy to combat childhood obesity. However, its effectiveness has long been controversial. This paper aims to examine the effectiveness of long-term (≥12 months) school-based PA interventions on body mass index (BMI) in primary school children, who are gaining BMI. METHODS Original papers were retrieved from PubMed, Google Scholar, the Cochrane Library and Web of Science, published between 1990 and 2015. The inclusion criteria were those research studies that were: randomized controlled trials (RCTs), conducted in primary school settings, had valid data on BMI at baseline and at the final follow up (or on BMI changes), and involved PA intervention that lasted for at least 12 months. RESULTS Out of 11,158 potentially eligible articles, 18 papers were included in the analysis, involving 22,381 primary school children with intervention durations ranging from 12 to 72 months. Compared to the control groups, the BMI increment was 2.23 kg/m(2) less in the intervention groups (p < 0.05). The heterogeneity was high across the studies (99.8 %), but declined after sub-group analyses. The intervention type, intervention duration, and weekly PA intervention time were among the factors leading to the heterogeneity. CONCLUSION Long-term school-based interventions containing PA as a core component appear to be effective in achieving healthier BMI. However, the results should be interpreted with caution due to the high heterogeneity among the studies. More high quality school-based RCTs among diverse populations are needed to improve the homogeneity and to yield a more robust conclusion.