Abstract
Background and aim. The prevalence of overweight and obesity increased three-fold among Finnish adolescents during the past three decades. The aim of the present study was to evaluate whether this secular trend differed between sociodemographic subgroups of adolescents. Methods. Mailed surveys were conducted among nationally representative samples of 12–18 year olds biennially in 1979–2005 (N=3 105–8 390 per year, response rates 88%–66%). Body mass index was calculated from self-reported weight and height, and overweight (including obesity) was defined according to the IOTF reference for children. Associations between sociodemographic factors and secular trend in the prevalence of overweight were tested by logistic regression including interaction terms between survey year and sociodemographic variables. Results. Throughout the study period a higher prevalence of overweight, as compared with the respective reference groups, was observed among adolescents from rural areas, Western or Eastern Finland; or from lower socioeconomic status families (as measured by father's/guardian's education or occupational status or by mother's education); adolescents reporting lower school achievement, attending vocational school or not going to school at all; adolescents whose fathers were not employed outside home; and among girls living in non-nuclear families or whose mothers were unemployed/laid-off or retired/on long-lasting sick leave. The statistically significant interactions between survey year and sociodemographic variables on the prevalence of overweight were few and inconsistent. Conclusion. The prevalence of overweight varied across sociodemographic subgroups of adolescents but in general no sociodemographic differences in the trends over time were observed. These results suggest that factors underlying the increasing trend of overweight have affected the entire adolescent population.