Tests of the effects of adolescent early alcohol exposures on adult outcomes

Aims: To determine whether early adolescent alcohol use contributes to adult alcohol use, misuse and other adult substance-related and social outcomes. Design: In a longitudinal study of twins assessed at target ages 11, 14 and 24 years, two techniques adjusted for confounding factors: a propensity score (PS) adjusting for the effects of measured background covariates and co-twin control (CTC) adjusting for confounding by unmeasured (including genetic) factors shared within early alcohol exposure-discordant pairs. Setting: The community-based Minnesota Twin Family Study. Participants: A total of 1512 (50.3% female) twins. Measurements: Early adolescent alcohol exposures, adult substance-related and social outcomes and background variables reflecting behavioral, familial and environmental characteristics. Findings: Background covariates unbalanced between those with and without early alcohol exposure were balanced through PS-based weighting, leaving several adult outcomes related to substance use or social functioning remaining significantly associated with early alcohol exposure. Similarly, the within-pair individual-level component of a CTC indicated that early alcohol-exposed twins had higher risk than their non-exposed co-twins for several, but not all, of the same adult outcomes. For example, early alcohol use was associated with an adult index of alcohol use in both PS-weighted (β=0.57, P<0.001) and CTC (β=0.21, P=0.031) analyses. Conclusions: Early alcohol exposures predict adult alcohol problems and related outcomes, despite stringent adjustment for measured and non-measured sources of potential confounding using propensity score and co-twin control. Contrasting the methods indicated that exposure effect estimates from PS application were likely biased by unmeasured confounding factors.