The television-to-exercise ratio is a predictor of overweight in adolescents: Results from a prospective cohort study with a two year follow up

ObjectiveTo determine whether the ratio of television-to-exercise predicted overweight in adolescents.MethodProspective cohort study with two years of follow-up of 1276 thirteen and sixteen year olds in Flanders, Belgium. Self reported weight, height, and the television-to-exercise ratio were registered in 2003. The main outcome measure was being overweight in 2005.ResultsIn the lowest quartile of the television-to-exercise ratio each 7 h of television were accompanied by at least 2.5 h of exercise per week. In the second quartile the Relative Risk (RR) of being overweight after two years, adjusted for age, sex and BMI at baseline, was 2.7 (95%CI: 0.9 to 7.6). In the third quartile the adjusted RR was 5.4 (95%CI: 2.0 to 14.4). In the highest quartile the adjusted RR was 8.9 (95%CI: 3.4 to 23.3). The adjusted RR was 5.2 (95%CI: 1.8 to 15.3) for the 9.3% subjects who reported no exercise.Seventy-two percent of the incidence of overweight in the sample could be attributed to a television-to-exercise ratio in excess of 2.3.ConclusionsOne extra hour of exercise per week could reduce the two year cumulative incidence of overweight in adolescents by 14%. Two and a half hours of exercise are needed to compensate for 7 h of television per week to protect against overweight.