Lars Bo Andersen and colleagues (July 22, p 299)1
show a graded negative association, independent of adiposity, between physical activity and a composite score of cardiovascular risk factors among 1732 schoolchildren.
These findings might suggest that physical activity acts as an independent protective factor and not only through obesity prevention. However, the results are not consistent with previous reports in children. Of note, a cross-sectional study consisting of 1015 UK schoolchildren suggested that the relation between cardiorespiratory fitness and five cardiovascular risk factors was mediated by adiposity.2
Data from the Aerobics Centre Longitudinal Study over 11 years of follow-up showed no association between adolescent cardiorespiratory fitness and adult cholesterol, blood pressure, and glucose concentrations, although adolescent adiposity was moderately related to selected adult risk factors.3
Nevertheless, higher fitness in adolescence seemed to be associated with lower levels of adiposity in adulthood,3
thus demonstrating the importance of childhood physical activity. In a prospective cohort study with 15 years' follow-up,4
young adults with poor fitness at baseline were threefold to sixfold more likely to develop diabetes, hypertension, and the metabolic syndrome in middle age than those with high fitness, although further adjustment for body-mass index diminished these associations to twofold.
It is therefore likely that physical inactivity (or low fitness) and obesity are related to cardiovascular risk via the same mechanisms, and that inconsistencies in published data could be a result of measurement problems and limited sample sizes.
I declare that I have no conflict of interest.