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 χ (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.