Volume, Patterns, and Types of Sedentary Behavior and Cardio-Metabolic Health in Children and Adolescents

Introduction Cardio-metabolic risk factors are becoming more prevalent in children and adolescents. A lack of moderate-to-vigorous intensity physical activity (MVPA) is an established determinant of cardio-metabolic risk factors in children and adolescents [1]. Less is known about the relationship between sedentary behavior and cardio-metabolic health. Therefore, the objective was to examine the independent associations between volume, patterns, and types of sedentary behavior with cardio-metabolic risk factors among children and adolescents.

Methods Results are based on 2527 American children and adolescents (6-19 years old) from the 2003/04 and 2005/06 National Health and Nutrition Examination Surveys (NHANES). A cardio-metabolic risk score (CRS) was calculated based on age- and sex-adjusted waist circumference, systolic blood pressure, non-high-density lipoprotein cholesterol, and C-reactive protein values. The total volume of sedentary behavior, the volume of sedentary behavior accumulated in bouts lasting ≥30 minutes, and the total volume of MVPA were measured using Actigraph AM-7124 accelerometers (Actigraph, Ft. Walton Beach, FL). These uniaxial accelerometers recorded average intensities in one minute intervals over 7 consecutive days. A cutpoint of <100 counts per minute was used to define sedentary behavior. A regression equation developed by Freedson and colleagues [2] was used to convert accelerometry counts into METS, and MVPA was defined as ≥4.0 METS. The volume for the two main types of sedentary behavior (TV, computer) were measured by questionnaire. A series of logistic regression models were used to examine associations.

Results MVPA predicted high (top quartile) CRS after adjusting for sedentary behavior measures and other confounders (P<0.05). However, the total volume of sedentary behavior and the volume of sedentary behavior accumulated in bouts lasting ≥30 minutes were not predictors of high CRS after adjusting for MVPA and other confounders (P>0.1). For types of sedentary behavior, TV use but not computer use was a predictor of high CRS after adjusting for MVPA and other confounders. Children and adolescents who watched ≥4 hours per day of TV were 2.53 (95% confidence interval: 1.45-4.42) times more likely to have high CRS than those who watched <1 hour per day. TV use was poorly correlated (r=0.08) with total volume of sedentary behavior assessed by accelerometry.

Discussion and Conclusion Excessive TV use and low MVPA were independently associated with cardio-metabolic risk in this large and representative sample of children and adolescents. At this time, TV use and MVPA appear to be two separate behaviors that need to be targeted with different interventions and policies. References [1] Andersen LB, Harro M, Sardinha LB, Froberg K, Ekelund U, Brage S, Anderssen SA. Physical activity and clustered cardiovascular risk in children: a cross-sectional study (The European Youth Heart Study). Lancet, 2006; 368: 299-304. [2] Freedson P, Pober D, Janz KF. Calibration of accelerometer output for children. Med Sci Sports Exerc, 2005; 37: S523-S530.