Early environmental influences contribute to covariation between internalizing symptoms and alcohol intoxication...

The association between alcohol use and internalizing symptoms during adolescence varies across studies, and the causes underlying this association remain unclear. The current study examines the relationship between symptoms of anxiety and depression and intoxication frequency in a sample of Swedish twins assessed longitudinally from ages 13-14 to 19-20. The objectives of the study were to assess the stability of genetic and environmental influences on each trait across adolescence; to investigate whether these traits share genetic and/or environmental liabilities; and to explore quantitative changes in the shared liability over time. We found that the magnitude of genetic influences on internalizing symptoms remained relatively stable across adolescence, while their impact on intoxication frequency was dynamic. Symptoms of anxiety and depression were influenced by unique environmental factors, while both shared and unique environmental factors influenced intoxication frequency. Genetic and environmental innovation and attenuation were observed for both traits. While no significant genetic correlation was observed between traits, unique environmental factors did contribute to a shared liability. This environmental correlation was positive and moderate (r(E)=0.41) in the early assessment, but decreased and changed direction at later waves (r(E)=-.04 to -.01). The genetic and environmental factors underlying internalizing symptoms and intoxication frequency appear to be developmentally dynamic. Early environmental factors contribute to the association between these traits, but this shared liability diminishes across adolescence.