The Nature of the Environment: Exploring How Exposure to Drugs in Neighborhoods Changes the Heritability of Adolescent Substance Use Initiation

Background: The influence of neighborhoods on child and adolescent behavior have long been part of ecological models (Bronfenbrenner, 1986) of development. Studies have consistently found that lower levels of neighborhood socioeconomic status (Brooks-Gunn, Duncan, Klebanov, & Sealand, 1993) are associated with increases the prevalence of substance use in adolescence (Kelly et al., 2011; Xue, Zimmerman, & Caldwell, 2007). Additional neighborhood characteristics important in the initiation of substance use are the degree of social disorganization in the neighborhood (Lambert, Brown, Phillips, & Ialongo, 2004), as well as the visibility (Saxe et al., 2001), and availability of drugs (Gillmore et al., 1990) in the neighborhoods that children and adolescents grow up. Although previous studies have found that genetic and familial factors influence the initiation and regular of use of substances in adolescence, few studies have examined how the relative influence of genetic and familial factors differ by environmental exposure. In the present study we explore how genetic and familial risks are differentially expressed in neighborhoods where drugs are a problem. 

Method: For this study, data come from adolescent and young adult (12- to 20-year-olds, mean age 16.0 SD=1.5, n=749) twin pairs from the National Longitudinal Study of Adolescent Health.  This study used behavioral genetic methods to decompose the variance in a measured behavior into genetic, familial, or unique effects. Based on parental responses to whether the family lived in a neighborhood where drugs were a common problem two groups were created of twin pairs differentially exposed to neighborhood conditions. Substance-specific, age-moderated multi-group structural equation models were fitted to estimate the magnitude of genetic and environmental effects on cigarette use initiation, alcohol use initiation, and marijuana use initiation.

Results:  About a third (36%) of the sample grew up in neighborhoods where drugs were common. There were no significant differences by neighborhood exposure on percent female, mean age, rates of cigarette use or alcohol use initiation, or paternal use of cigarettes, but adolescents exposed to drugs in the neighborhood had higher rates of maternal use of cigarettes, and had higher rates of marijuana initiation.  According to the best fitting models, genetic effects were stronger for the initiation of cigarettes and marijuana, but not for alcohol initiation, in neighborhoods where drugs are a problem compared to neighborhoods where drugs are not a problem.

 

Conclusion: Few previous studies have examined how environmental conditions differentially influence the expression of genetic effects. This study is among the first to formally test and find that the influence of genes depends on the level of risk in the environment for some substances commonly used in adolescence.  The implication of this work for promoting the healthy development for youth includes underscoring the importance of providing access to healthy environments.