Direction of the association between body fatness and self-reported screen time in Dutch adolescents

Longitudinal data of 465 Dutch adolescents (mean age at baseline 13 years, 53% boys) was used. Body fatness (objectively measured BMI, four skin folds and waist- and hip circumference), self-reported time spent watching TV and computer use, and aerobic fitness (shuttle run test) were assessed in all participants at three time points during 12 months. Multi-level linear autoregressive analyses was used to examine whether screen time predicted body fatness in the following time period and whether body fatness predicted screen time. Analyses were performed for boys and girls separately and adjusted for ethnicity and aerobic fitness.Time spent TV viewing did predict changes in BMI and hip circumference in boys, but not in girls, in the subsequent period. Computer time significantly predicted increases in skinfolds in boys and girls and increases in BMI in girls. Body fatness did not predict any changes in screen time.The present study only partly supports the widely posited hypothesis that higher levels of screen time cause increases in body fatness. In addition, this study demonstrates that high levels of body fatness do not predict increases in screen time.The prevalence of overweight and obesity among youth has increased worldwide. Importantly, obesity in youth is known to track into adulthood [1] and is associated with serious health complications such as glucose intolerance, type 2 diabetes and cardiovascular diseases later in life [2]. A 'Westernized' lifestyle of excessive energy intake and sedentary behavior is hypothesized as an important factor in the worldwide increasing prevalence of overweight and obesity [3-7].A number of cross-sectional and longitudinal studies have demonstrated the positive association between time spent sedentary and measures of body fatness among youth [8-15]. Hume et al [16] showed a dose-response association between screen time and overweight among girls. TV viewing is indicated as the most important sedentary behavior affecting body