The Relationship Between Adolescent Alcohol Use And Functioning In Later-Young Adulthood: Disentangling Confounding Influences From Causal Processes Using A Twin Sample

Abstract

The vast majority of individuals initiate alcohol consumption for the first time in adolescence, and heavy alcohol use during this time period is relatively common. Given the widespread nature of its use and evidence that adolescents may be especially vulnerable to its effects, there is concern about the long-term detrimental impact of adolescent drinking on adult functioning. Unfortunately, the research surrounding this topic has been affected by limited attention to consequences outside of adult substance use, as well as a lack of methodology that allows for conclusions about a causal impact of adolescent drinking, which is especially problematic given evidence suggesting that familial influences such as genetic risk may confound the relationship. A series of three studies were conducted to address these limitations and elucidate the nature of the relationship between adolescent drinking and later functioning. All three studies utilized a prospective longitudinal sample drawn from the Minnesota Twin Family Study, consisting of 2,764 twins assessed in two cohorts at regular follow-ups from age 17 to age 29 (older cohort) or age 11 to age 29 (younger cohort). A broad range of adult measures was included tapping substance use and substance use disorders, antisocial behavior, mental health issues and personality, socioeconomic status, and social functioning. Using biometric modeling, the first study examined the familial influences on the association between a measure of adolescent alcohol consumption and each of the measures of adult adjustment. Delineating the source of the covariation extends the literature by furthering understanding of the mechanisms that link adolescent drinking with later functioning while also providing an empirical justification for the use of methodologies that control for familial influences. The results revealed that genetic factors and unique environmental influences were generally most important in explaining the relationship between adolescent drinking and later functioning. In the second study, evidence for a causal relationship between adolescent drinking and adult outcomes was examined through a series of co-twin control analyses. Measures of early initiation of drinking and intoxication, as well as an index of level of alcohol consumption, were all predictive of the adult measures, but the co-twin control analyses suggested that many of the individual associations were influenced by familial confounding. However, relationships consistent with causal processes were present for each of the adolescent drinking measures across multiple domains of adult functioning, with significant effects most frequently observed with the measure of adolescent alcohol consumption. In the third study, mechanisms grounding the relationship between adolescent drinking and later functioning were further examined by focusing on mediators between adolescent drinking and later-young adulthood. Drinking in emerging adulthood partially mediated the relationship with all of the adult domains, except for socioeconomic status, and co-twin control analyses revealed that this mediating effect was generally consistent with a causal process. In contrast, when controlling for drinking during emerging adulthood, the unique effects of adolescent drinking on later functioning were attenuated, although there were some specific effects for substance use measures. In summary, this investigation extends the current literature by demonstrating that adolescent drinking is associated with multiple domains of later-young adult functioning, genetic factors strongly influence the association, evidence is consistent with the conclusion that adolescent alcohol consumption has a causal effect on a limited set of facets of adult adjustment, and continued drinking in emerging adulthood mediates the relationship.