Like me, like you - relative importance of peers and siblings on children's fast food consumption and screen time but not sports club participation depends on age

Background Lifestyle interventions to prevent paediatric obesity often target family and peer settings; their success is likely to depend on the influence that peers and families exert on children's lifestyle behaviors at different developmental stages. Objective First, to determine whether children's lifestyle behavior more closely resembles their peers' or siblings' behaviors. Secondly, to investigate longitudinally whether children's behavioral change is predicted by that of their peers or their siblings as they grow older. Methods The European prospective IDEFICS/I.Family cohort (baseline survey: 2007/2008, first follow-up: 2009/2010, and second follow-up: 2013/2014) aims at investigating risk factors for overweight and related behaviors during childhood and adolescence. The present investigation includes 2694 observations of children and their siblings aged 2 to 18 years. Peers were defined as same-sex, same-age children in the same community and identified from the full cohort. The longitudinal analysis (mean follow-up time: 3.7 years) includes 525 sibling pairs. Children's lifestyle behaviors including fast food consumption (frequency/week), screen time (hours/week) and sports club participation (hours/week) were assessed by questionnaire. Data were analyzed using multilevel linear models. Results Children's lifestyle behavior was associated with the respective behavior of their peers and sibling for all 3 behaviors. For fast food consumption, the peer resemblance was more than 6-fold higher than the sibling resemblance and the peer resemblance surpassed the sibling resemblance by the age of 9-10 years. The similarities with peers for fast food consumption and screen time steadily increased, while the similarities with siblings steadily decreased with increasing age of the children (P-interaction