title: Stability of television viewing and electronic game/computer use in a prospective cohort study of Australian children: relationship with body mass index.
abstract: BACKGROUND
  While much cross-sectional data is available, there have been few longitudinal investigations of patterns of electronic media use in children. Further, the possibility of a bi-directional relationship between electronic media use and body mass index in children has not been considered. This study aimed to describe longitudinal patterns of television viewing and electronic game/computer use, and investigate relationships with body mass index (BMI).
  
  
  METHODS
  This prospective cohort study was conducted in elementary schools in Victoria, Australia. 1278 children aged 5-10 years at baseline and 8-13 years at follow-up had their BMI calculated, from measured height and weight, and transformed to z-scores based on US 2000 growth data. Weight status (non-overweight, overweight and obese) was based on international BMI cut-off points. Weekly television viewing and electronic game/computer use were reported by parents, these were summed to generate total weekly screen time. Children were classified as meeting electronic media use guidelines if their total screen time was </=14 hrs/wk.
  
  
  RESULTS
  Electronic media use increased over the course of the study; 40% met guidelines at baseline but only 18% three years later. Television viewing and electronic game/computer use tracked moderately and total screen time was positively associated with adiposity cross-sectionally. While weaker relationships with adiposity were observed longitudinally, baseline z-BMI and weight status were positively associated with follow-up screen time and baseline screen time was positively associated with z-BMI and weight status at follow-up. Children who did not meet guidelines at baseline had significantly higher z-BMI and were more likely to be classified as overweight/obese at follow-up.
  
  
  CONCLUSIONS
  Electronic media use in Australian elementary school children is high, increases with age and tracks over time. There appears to be a bi-directional association suggesting that interventions targeting reductions in either screen time or adiposity may have a positive effect on both screen time and adiposity.
authors.affiliation: Deakin University, 221 Burwood Hwy, Burwood Vic 3125, Australia. kylie.hesketh@deakin.edu.au
authors.forename: Kylie
authors.initials: K
authors.lastname: Hesketh
authors.forename: Melissa
authors.initials: M
authors.lastname: Wake
authors.forename: Melissa
authors.initials: M
authors.lastname: Graham
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Waters