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To the Editor.—Dr Andersen and colleagues1 address 2 important questions—whether ethnic groups are determinants of the level of physical activity and whether physical activity and television watching are determinants of body composition.
Limited data are available concerning physical activity and television watching in children and adolescents of countries other than the United States, and we think that, as in other cases, it is important to analyze results of this issue in other populations. Seven years ago in Zaragoza, Spain, we carried out a representative cross-sectional survey of adolescents (537 boys and 541 girls) aged 13 and 14 years.2 - 4
In our survey of a homogeneous white population, we have observed very similar results of the level of physical activity among ethnic groups as those in the study by Anderson et al taking into account socioeconomic status. We found that boys and girls of the lowest socioeconomic status were more sedentary and spent more time watching television than those of higher socioeconomic status.2 Therefore, the question now is whether ethnic groups are determinants of the level of physical activity or if the variant activity levels instead were caused by differences in social class.
When considering the relationship between physical activity and body composition, Andersen et al assessed physical activity by means of a questionnaire in which they asked how many times per week children "played or exercised enough to make them sweat or breathe hard." From this point of view, we think it would be better to use validated questionnaires that give us information about total energy expenditure2 - 4 or even, when possible, other methods such as heart rate recording5 or accelerometry. Despite these methodological comments, we have observed in our study the following similar results: (1) the amount of physical activity was not related to body mass index (BMI, which is calculated as weight in kilograms divided by the square of the height in meters) in either boys or girls, but it was related significantly to fat deposition in adolescent girls but not in boys3 ; and (2) the time spent watching television was related significantly with BMI in girls and with body fat percentage in both boys and in girls. In all cases, the effect was higher in girls than in boys.4
Despite the lack of causal evidence showing that viewing television is a risk factor for obesity, health programs should aim to substitute less sedentary activities for sitting in front of the television, computers, videocassettes, and video games, not only in the United States but also in other developed countries such as those in Europe.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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