BMI-specific associations between health-related behaviours and overweight - a longitudinal study among Norwegian adolescents

Objective: To investigate BMI-specific associations between health-related behaviours in early adolescence and the likelihood of overweight in mid-adolescence in a sample of Norwegian adolescents. Design: Longitudinal study of 393 adolescents recruited from schools in Telemark County, Norway. Parents reported baseline data on children's behavioural variables and background data (at age 12-13 years). Dietary data were reported by means of a retrospective FFQ. Eating patterns were identified using principal component analysis. Height and weight were measured at baseline and 3-year follow-up. BMI-specific differences in health-related behaviours (eating patterns, physical activity and screen time) at baseline were analysed using cross-tabulation and Pearson's chi(2) test (Fisher's test). Associations between early health-related behaviours and the likelihood of later overweight were examined using multiple logistic regression. Setting: Primary and secondary schools, Telemark, Norway. Subjects: Children (n 393) in 7th grade (mean age 12.7 (SD 0.3) years), followed up in 10th grade, and parents. Results: A moderate to high intake of a varied Norwegian eating pattern combined with moderate-to-vigorous physical activity >= 1 h/d in the 7th grade were associated with a reduced likelihood of being overweight in the 10th grade, but only among already overweight adolescents (adjusted OR=0.2; 95 % CI 0.1, 1.0). Screen time of >3 h/d in the 7th grade was associated with an increased likelihood of subsequent overweight only among adolescents with an initial normal weight (adjusted OR=2.8; 95 % CI 1.1, 7.3). Conclusions: BMI-specific associations were observed between health-related behaviours in early adolescence and the likelihood of being overweight in mid-adolescence.