Implication for practice and research

• Increasing youth engagement in physical activity may have beneficial effects on cardiometabolic health outcomes.

• Further research is needed to examine associations between objectively measured sedentary time and cardiometabolic health outcomes, adjusting for physical activity.

Context

In recent years, there has been increasing interest in the effects of sedentary behaviour on children's health, defined as sitting behaviours that require low levels of energy expenditure (≤1.5 METs).1 There is some evidence that sedentary behaviours may be detrimental to children's health, though the majority of associations observed are derived from cross-sectional studies examining television viewing and adiposity.2 This study adds to the literature by examining cross-sectional and prospective associations between objectively measured moderate- to vigorous physical activity (MVPA) and sedentary time, and cardiometabolic risk factors in youth aged 4–18 years.

Findings

Time spent in MVPA was associated with all cardiometabolic outcomes, independent of sedentary time. Time spent sedentary was positively and significantly associated with fasting insulin after adjusting for confounding variables. However, this association was not significant after additional adjustment for MVPA. Higher MVPA was associated with significantly lower cardiometabolic health outcomes across tertiles of sedentary time. Differences in outcomes between high and low tertiles of MVPA were greater the lower the sedentary time. MVPA and sedentary time were not associated with a higher waist circumference in the prospective analyses. However, baseline waist circumference was associated with increased waist circumference at follow-up.

Commentary

This study contrasts previous research that has reported negative associations between specific sedentary behaviours, such as television viewing and health outcomes in children.2 These findings also contrast research conducted in adult populations that suggest objectively measured sedentary time is inversely associated with cardiometabolic health outcomes.3 However, the findings are consistent with those that found no associations between overall volume and patterns of sedentary behaviour and cardiometabolic health risk factors in youth aged 6–19 years.4

The strengths of this study include the large and diverse sample size, the meta-analytical approach, and the objective measurement of sedentary time and MVPA. However, the approach adopted to analyse the raw data may have affected the results. Although there is no consensus on a definitive definition of MVPA using accelerometry, cut-points used in the literature are often age specific. However, in this study a universal cut-point of ≥3000 CPM was used to define MVPA regardless of the wide age range within the sample. This approach is likely to result in an underestimation of MVPA. Moreover, 60 min of consecutive zeros to identify non-wear time is liberal, and non-wear may be incorrectly classified as sedentary time. Examining the associations by age group (eg, children, adolescents) could also have been undertaken, as associations between sedentary time and health may take time to develop and may be present in adolescents, but perhaps not in children. Overall, this study highlights the importance of physical activity on cardiometabolic health among youth. Increasing physical activity among children of all ages should be a priority around the world.