We also found support for a significant additive interaction between the GRS and neighborhood social cohesion that was associated with frequency of cigarette smoking. Genetic risk for smoking was less influential for individuals who lived in neighborhoods with higher levels of social cohesion. To our knowledge, no previous study has specifically examined the relationship between genetic risk factors and neighborhood social cohesion, as measured here. However, there have been studies that have examined the interaction between genetic risk factors and related environmental risk factors, such as rural residencies.25, 41 In these studies, environmental contexts characterized by accountability to your peers, neighbors and community diminished the genetic influences on substance use. We believe this to be an example of social control,39 whereby aspects of the social environment restrict the opportunity to express one's genetic predisposition for a risk behavior (cigarette smoking). These results, taken together with previous studies that have found an inverse relationship between social support and substance use in adolescents,26 suggest that these supportive relationships may act as protective factors against the risk of smoking behaviors. However, in light of previous studies that have examined the mechanism behind neighborhood social cohesion,52 this is likely contingent upon neighborhood antismoking attitudes.
