Physical activity at the government-recommended level and obesity-related health outcomes: a longitudinal study (Early Bird 37)
- Brad S Metcalf, University Medicine, Level 7, Derriford Hospital, Plymouth PL6 8DH, UK;
- Accepted 28 March 2008
- Published Online First 30 June 2008
Background: In the UK and USA, government guidelines for childhood physical activity have been set (⩾60 min/day at ⩾3 metabolic equivalents of thermogenesis (METs)), and body mass index (BMI) chosen as the outcome measure.
Aim: To determine the extent to which physical activity at the government-recommended intensity is associated with change in body mass/fat and metabolic health in pre-pubertal children.
Methods: Non-intervention longitudinal study of 113 boys and 99 girls (born 1995/96) recruited from 54 schools. Physical activity (Actigraph accelerometers), changes in body mass (raw and age/gender-standardised BMI), fatness (skin-fold thickness and waist circumference) and metabolic status (insulin resistance, triglycerides, cholesterol/HDL ratio and blood pressure – separately and as a composite metabolic z score) were measured on four annual occasions (5, 6, 7 and 8 years).
Results: Mean physical activity did not change over time in either sex. Averaging the 7-day recordings from four time points rather than one increased the reliability of characterising a child’s activity from 71% to 90%. Some 42% of boys and 11% of girls met the guideline. There were no associations between physical activity and changes in any measurement of body mass or fatness over time in either sex (eg, BMI standard deviation scores: r = −0.02, p = 0.76). However, there was a small to moderate inverse association between physical activity and change in composite metabolic score (r = −0.19, p<0.01). Mixed effects modelling showed that the improvement in metabolic score among the more active compared to the less active children was linear with time (−0.08 z scores/year, p = 0.001).
Conclusions: In children, physical activity above the government-recommended intensity of 3 METs is associated with a progressive improvement in metabolic health but not with a change in BMI or fatness. Girls habitually undertake less physical activity than boys, questioning whether girls in particular should be encouraged to do more, or the recommendations adjusted for girls.
Funding: Funding was provided by Diabetes UK, Bright Futures Trust, Smith’s Charity, Child Growth Foundation, Diabetes Foundation, Beatrice Laing Trust, Abbott, Astra-Zeneca, GSK, Ipsen and Roche. None of the sources funding this study had any involvement in its design, analysis, interpretation or writing.
Competing interests: None.
Ethics approval: Ethics approval was obtained.
Contributions: The authors have contributed as follows and have seen and approved the final version. BM: data entry, analysis and writing; LV; co-ordinator of the EarlyBird study/writing; JH: data entry and analysis; AJ: data collection; TW: director of the EarlyBird study/writing.