Intended for healthcare professionals


Preventing obesity in primary schoolchildren

BMJ 2010; 340 doi: (Published 24 February 2010) Cite this as: BMJ 2010;340:c819
  1. Esther M F van Sluijs, investigator scientist,
  2. Alison McMinn, career development fellow
  1. 1MRC Epidemiology Unit, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge CB2 0QQ
  1. esther.vansluijs{at}

    School based physical activity programmes are promising, but difficult to sustain

    Childhood obesity is rapidly increasing worldwide and is associated with a higher risk of several health problems, as well as with being obese as an adult.1 Obesity is at least partly caused by an energy imbalance, which makes tackling unhealthy diets and low levels of physical activity in children key public health objectives. Physical activity in childhood has also been independently associated with health outcomes,2 3 so promoting physical activity probably has benefits beyond weight control. However, promoting physical activity in children has proved challenging, and we have little evidence available for effective strategies.4

    In the linked cluster randomised trial on (doi:10.1136/bmj.c785), Kriemler and colleagues evaluated a school based physical activity programme targeted at preventing excessive weight gain in Swiss primary schoolchildren.5 The multi-component intervention was conducted over one school year and focused on three main aspects: increasing the quality and amount of physical education, introducing short daily activity breaks during academic lessons, and providing children with daily physical activity homework. The strengths of the study include the high level of implementation of the intervention, its high degree of integration into the school system, and the high quality evaluation conducted—something often lacking in previous research.4 The authors showed significant benefits on body fat, fitness, physical activity, and cardiovascular risk status.5

    Kriemler and colleagues’ findings support the results of a recent meta-analysis that showed a significant short term protective effect of school based interventions on childhood obesity.6 This has also been shown in a subgroup of five evaluations of interventions similar to those in the present study.7 8 9 10 11 Kriemler and colleagues add to this literature by applying a wide range of more precise measures in a well designed evaluation, which enables a better picture of the effects of the intervention to be created.

    Wider implementation of this intervention may be possible, although it poses several challenges. Most importantly, it would require changes to the school curriculum. Although efforts are being made to lengthen the time allocated to physical education in school, providing physical education classes of 45 minutes and up to 25 minutes of activity breaks each day is quite a step away from the weekly two hours of physical education currently recommended in primary schools in the United Kingdom.12 It would substantially add to the school timetable. Although the acceptability of these additional lessons was high in Kriemler and colleagues’ study,5 it is unclear how feasible wider implementation would be. Further research into the feasibility and acceptability of such a strategy in different countries is needed.

    This study provides an excellent example of the high quality evaluations needed to make advances in this field. However, it does have limitations, which need to be dealt with in future studies. Although the overall follow-up rate was high, less than 70% of children provided valid data on physical activity or the cardiovascular risk score, with attrition being particularly high in the control group. Moreover, the authors do not report a thorough process evaluation (a study of the potential implementation and feasibility of the intervention), which would have helped to shed light on potential challenges with implementation, the acceptability of the various components, and perceived effectiveness. This information could have helped inform future development and implementation of the intervention.

    At this stage, Kriemler and colleagues report only the short term results. The few other studies that have included follow-up beyond the intervention showed no overall effect,6 suggesting that any improvements obtained are difficult to sustain. The important question is therefore how we can effectively change children’s physical activity behaviour. Kriemler and colleagues’ study, along with previous ones, shows that increasing “compulsory” activity at school increases physical activity in the short term. Continuing interventions for longer seems to be even more effective.6 Continual interventions throughout primary school and potentially secondary school may be the only way to increase physical activity and prevent obesity in the long term. However, the cost implications and health benefits of such a strategy are unclear because few studies have included a cost effectiveness evaluation and long term follow-up.

    The effectiveness of a school based strategy in inducing long term behavioural change is doubtful. Removal of the intervention at any stage will require the children themselves to change their physical activity behaviour during and outside of school to maintain the higher activity level attained. Without teaching skills for behavioural change and involving family members, it is unclear whether school based interventions can be successful in the long term.4 Successfully tackling childhood obesity will require further research in these areas.


    Cite this as: BMJ 2010;340:c819


    • Research, doi:10.1136/bmj.c785
    • Competing interests: All authors have completed the Unified Competing Interest form at (available on request from the corresponding author) and declare: (1) No financial support for the submitted work from anyone other than their employer; (2) No financial relationships with commercial entities that might have an interest in the submitted work; (3) No spouses, partners, or children with relationships with commercial entities that might have an interest in the submitted work; (4) No non-financial interests that may be relevant to the submitted work.

    • Provenance and peer review: Commissioned; not externally peer reviewed.


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