Children's physical activity and sedentary time and cardiometabolic risk factors.

OBJECTIVE: To examine the associations of moderate-to-vigorous physical activity (MVPA) and time spent sedentarily with cardiometabolic risk factors in children and adolescents.

DESIGN: The data from 14 studies were pooled. This summary is of the associations between baseline activity levels and cardiometabolic risk factors measured in the cohort that was followed for a mean 2.1 years.

SETTING: The data were drawn from studies (1998-2009) in Australia, Brazil, Europe, and the United States by the International Children's Accelerometry Database (ICAD) Collaborators.

PARTICIPANTS: At baseline, the 20,871 participants in 14 studies were 4 to 18 years of age. Baseline and follow-up data on waist circumference were available for 6413 participants from 7 studies.

ASSESSMENT OF RISK FACTORS: The children's time spent in activity and time spent sedentarily were objectively measured through the use of accelerometers (actigraphs) from which physical activity counts per minute (cpm) could be obtained in a standard way. Sedentary time was defined as all minutes showing <100 cpm, whereas MVPA time was minutes with >3000 cpm. Anthropometric and cardiometabolic measures were initially recorded at baseline.

MAIN OUTCOME MEASURES: The main end points were the cardiometabolic outcomes of abdominal adiposity (waist circumference), glucose metabolism and lipid metabolism (fasting insulin, triglycerides, and HDL cholesterol), and resting systolic blood pressure (SBP). In each study the relations between cpm, MVPA, and sedentary time were adjusted for each other. Regression coefficients were calculated to allow cross-sectional random effects meta-analysis adjusted for sex, age, and monitor-wear time, and further adjusted in the prospective study by baseline values and follow-up time.

MAIN RESULTS: At a median of 2.1 years of follow-up (range, 0.3-8.0 years), time spent in MVPA at baseline was not associated with waist circumference (β = 0.00024; 95% confidence interval [CI] -0.0057 to 0.0062). Similarly, baseline sedentary time was not associated with follow-up waist circumference (β = -0.0024; 95% CI, -0.0057 to 0.0010). A greater waist circumference at baseline was not associated with time spent in MVPA at follow-up (β = -0.0037; 95% CI, -0.60 to 0.052), but was associated with more sedentary time at follow-up (β = 0.40; 95% CI, 0.19-0.61). At baseline, total physical activity cpm and MVPA were negatively associated with baseline waist circumference, SBP, and serum levels of fasting insulin and triglycerides. Baseline time per day in sedentary activity was positively associated with fasting insulin level but not with any other cardiometabolic risk factor.

CONCLUSIONS: Although children's level of physical activity and time spent sedentarily were cross-sectionally related to some baseline cardiometabolic risk factors, they did not predict waist circumference measured at follow-up. However, waist circumference at baseline did predict more sedentary time at follow-up.