Sibling effects on smoking in adolescence: evidence for social influence from a genetically informative design
Aims Behavioral genetic research has suggested that sibling effects on smoking may reflect social rather than genetic processes. We utilize a genetically informative sample of adolescents to test this proposition, focusing on sibling relationship processes (social connectedness) shown to be influential in studies of deviancy. Design A combined twin-sibling design was employed to disentangle genetic and non-genetic effects. Participants We utilized a sample of 1421 adolescent sibling pairs participating in the US National Longitudinal Study of Adolescent Health (Add Health). These sibling pairs represent a spectrum of genetic relatedness and include monozygotic twins, dizygotic twins, biological siblings, half-siblings and unrelated siblings. Measurements Participants completed self-report questionnaires on smoking behavior, quality of relationship with their sibling (social connectedness) and peer and parental smoking. Findings Main effects of both shared environment and genetics were found on adolescent smoking frequency. Social connectedness between siblings moderated shared environmental influences on smoking frequency at each time period, as well as on change in smoking frequency. Shared environmental effects were more pronounced when siblings reported high levels of social connectedness. These environmental sibling effects on smoking were significant after controlling for parent and peer smoking. Conclusions This report extends prior research on sibling effects on smoking by identifying specific relationship dynamics that underlie transmission of risk within sibships and providing evidence that such relationship dynamics represent social rather than genetic processes.