Abstract
BackgroundBody Mass Index (BMI) is a common outcome when assessing associations between childhood overweight and obesity and physical activity patterns. However, the fat and fat-free components of BMI, measured by the Fat Mass Index (FMI) and Fat-Free Mass Index (FFMI), may show contrasting associations with physical activity, while ethnic groups may vary in both physical activity patterns and body composition. Body composition must therefore be evaluated when assessing the associations between childhood overweight and obesity and physical activity in multi-ethnic populations.MethodsThis cross-sectional study investigated associations of BMI, FMI and FFMI z-scores with extracurricular physical activity for 2171 London primary schoolchildren (aged 5–11 years) of black, South Asian and white/other ethnicity. Multilevel mixed-effects ordered logistic modelling was used, adjusting for age, sex and family and neighbourhood socioeconomic status as potential confounders.ResultsControlling for ethnicity and individual, family and neighbourhood socioeconomic confounders, actively commuting children had significantly lower Odds Ratios for being in high BMI (Odds Ratio (OR) = 0.678; 95 % Confidence Interval (CI) = 0.531 − 0.865; p − value = 0.002) and FMI z-score groups (OR = 0.679; 95 % CI = 0.499 − 0.922; p = 0.013), but not FFMI z-score groups, than passive commuters. Children doing sports less than once a week had lower Odds Ratios for being in high BMI (OR = 0.435; 95 % CI = 0.236 − 0.802; p = 0.008) and FFMI (OR = 0.455; 95 % CI = 0.214 − 0.969; p = .041) z-score categories compared to daily active children. Differences in FMI between groups did not reach the significance threshold. A trend towards statistical significance was obtained whereby children’s complete inactivity was associated with higher odds for being in higher BMI (OR = 2.222 : 95 % CI = 0.977 − 5.052; p = .057) and FMI z-score groups (OR = 2.485 : 95 % CI = 0.961 − 6.429; p = .060). FFMI z-scores did not show a similar trend with complete inactivity.ConclusionsActive commuting was objectively associated with lower adiposity, while more frequent extracurricular sports participation was correlated with greater fat-free mass accretion. These relationships were independent of ethnicity and individual, family or neighbourhood socioeconomic confounding factors.
Highlights
Body Mass Index (BMI) is a common outcome when assessing associations between childhood overweight and obesity and physical activity patterns
Study aim We aimed to study the association of physical activity (PA) with body composition in a multi-ethnic sample of United Kingdom (UK) primary schoolchildren
Descriptive statistics For 1889 Size and Lung Function in Children (SLIC) children who were healthy at the time of data collection, data were available for each of the anthropometric, body composition, PA and Index of Multiple Deprivation measures (87.0% of the total sample)
Summary
Body Mass Index (BMI) is a common outcome when assessing associations between childhood overweight and obesity and physical activity patterns. Body composition must be evaluated when assessing the associations between childhood overweight and obesity and physical activity in multi-ethnic populations. The limitations of using BMI in the study of childhood overweight and obesity are well-established [3], as it does not differentiate fat and fat-free body mass components [4, 5]. Both BMI itself and the thresholds at which high BMI is associated with ill-health vary with age, sex and ethnicity [6]. The different health implications of fat and fat-free mass make the distinction between them vital in the determination of the risks posed by adiposity, as obesity-related health risks are primarily the consequence of excessive fat accumulation rather than total weight [4, 5]
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