Social Relationships Moderate Genetic Influences on Heavy Drinking in Young Adulthood

Abstract

Objective: Social relationships, such as committed partnerships, limit risky behaviors like heavy drinking, in part, because of increased social control. The current analyses examine whether involvement in committed relationships or social support extend beyond a main effect to limit genetic liability in heavy drinking (gene-environment interaction) during young adulthood.

Method: Using data from the young adult wave of the Finnish Twin Study, FinnTwin12 (n = 3,269), we tested whether involvement in romantic partnerships or social support moderated genetic influences on heavy drinking using biometric twin modeling for gene-environment interaction.

Results: Involvement in a romantic partnership was associated with a decline in genetic variance in both males and females, although the overall magnitude of genetic influence was greater in males. Sex differences emerged for social support: increased social support was associated with increased genetic influence for females and reduced genetic influence for males.

Conclusions: These findings demonstrate that social relationships are important moderators of genetic influences on young adult alcohol use. Mechanisms of social control that are important in limiting genetic liability during adolescence extend into young adulthood. In addition, although some relationships limit genetic liability equally, others, such as extensive social networks, may operate differently across sex.

Figure 1.

The classic univariate twin model depicting variance in traits partitioned into additive genetic (A), shared environmental (C), and unique environmental (E) components. Correlations between A fixed to 1 for monozygotic (MZ) twin pairs and .5 for dizygotic (DZ) twin pairs. Correlations between C fixed to 1 for both MZ and DZ twins.

Figure 2.

Figures show extended univariate model (left) and simplified bivariate model (right) with only the genetic components included for ease of display. Moderation is estimated through the β on each of the a, c, and e paths. In the bivariate case, the moderation can act on both the shared path between the moderator and trait (a₂₁) and the path unique to the trait (a₂₂). In the case when the extended univariate model is selected over the bivariate, all of the shared paths between trait and moderator (M) are collapsed into the means portion of the model.

Figure 3.

Results from gene–environment interaction models for heavy drinking. Bars in first row represent changes in raw variance of components across relationship status. Shaded areas in second row represent change in proportion of total variance explained by each component. Moderation effects constrained to be equal across sex. Moderation on A is significant (p < .001). Moderation on E is not significant (p = .055).

Figure 4.

Results from gene–environment interaction models for heavy drinking. Lines in first row represent changes in raw variance of components across social support (standardized). Shaded areas in second row represent change in proportion of total variance explained by each component. Moderation on A is significant for both women (p < .001) and men (p < .05). Moderation on E is only significant in women (p < .01).