Covariates and effect modifiers
Demographic, health, and lifestyle information on the study participants was collected using self-administered questionnaires completed by the parents (sex, duration of total physical activity [hours per week], highest education level of either parent [low: both parents reported less than 10 years of school; high: at least one of the parents reported more than 10 years of school; medium: the rest of the study participants with available information], and pubertal status of child, which was assessed based on parental reported questionnaire (signs of pubertal, e.g. pubic hair or menarche) [pubertal versus non-pubertal]). Height and weight were measured at the 10-year physical examination and were used to calculate the BMI of children.