Physical activity program for preschool children fails to reduce body mass index

Article Outline

• Reilly JJ, Kelly L, Montgomery C, Williamson A, Fisher A, McColl JH, et al. Physical activity to prevent obesity in young children: cluster randomised controlled trial. BMJ 2006;333:1041-3
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Reilly JJ, Kelly L, Montgomery C, Williamson A, Fisher A, McColl JH, et al. Physical activity to prevent obesity in young children: cluster randomised controlled trial. BMJ 2006;333:1041-3 

Question Among young children, does a physical activity intervention reduce body mass index?

Design Cluster randomized, controlled, single-blinded trial over 12 months.

Setting 36 nurseries in Glasgow, Scotland.

Participants 545 preschool children, mean age 4.2 years at baseline.

Intervention Enhanced physical activity program in nursery (three 30-minute sessions a week over 24 weeks) plus home-based health education aimed at increasing physical activity through play and reducing sedentary behavior.

Outcomes Body mass index, expressed as a standard deviation score relative to UK 1990 reference data. Secondary measures were objectively measured physical activity and sedentary behavior, fundamental movement skills, and evaluation of the process.

Results Group allocation had no significant effect on the primary outcome measure at 6 and 12 months or on measures of physical activity and sedentary behavior by accelerometry. Children in the intervention group had significantly higher performance in movement skills tests than control children at 6 month follow-up (P = .0027; 95% confidence interval 0.3-1.3) after adjustment for sex and baseline performance.

Conclusions Physical activity can significantly improve motor skills but did not reduce body mass index in young children in this trial.

Comment The obesity pandemic is threatening the current generation of children with shorter life expectancies than those of their parents. There is a paucity of published data evaluating the effectiveness of local school-based programmatic and policy change interventions. Even fewer studies have addressed nutrition and physical activity improvements in preschool and child care settings. This study, by Reilly and colleagues, was rigorously designed to try to address this critical gap in the literature. However, the study’s findings of a failure of the intervention to influence body mass index and, especially, physical activity levels seem contrary to much of the recent scholarship in this field. Several methodological weaknesses may explain the null findings, for example, insufficient intervention dose, less-than-ideal outcome measure selection, compromises to the fidelity of the intervention implementation to enhance generalizability and exportability, and inadequate power to detect modest effects in subsamples (sex and/or overweight status).

However, let’s not miss the forest for the trees. These findings represent yet another demonstration of the weak and, at best, transient salutary behavioral effects of self-limited programmatic and primarily individual-level interventions, especially in the absence of anchoring structural or systemic changes. Widespread and comprehensive changes in social norms and values supporting physical activity engagement, and undermining prolonged sitting, must ultimately permeate school, family, and community settings. That said, early evidence provides reason for optimism that preschool settings can be useful as part of a comprehensive obesity prevention strategy. Their captive audiences represent an important segment of the youth population, worthy of continuing investment and investigation to identify successful intervention models.