Abstract
INTRODUCTION: Extant twin research on the depression-smoking association in adolescents has been conducted in U.S. and European samples and considered depression as a unitary phenotype. This study explored genetic and environmental influences on covariation between smoking initiation and 4 depressive symptom dimensions (positive affect [PA], negative affect [NA], somatic features [SF], and interpersonal problems [IP]) in adolescent Chinese twins. METHODS: Questionnaires measuring current depressive symptoms and lifetime smoking initiation were administered to 602 twin pairs (M [SD] age = 12.2 (1.93) years, range 9-16 years). Cholesky bivariate decomposition models examined influences on each depressive symptom dimension, smoking initiation, and their covariation using age- and sex-adjusted threshold variables. RESULTS: Within-twin correlations between smoking initiation and each depressive symptom dimension were significant (|r|s = .29-.61). Bivariate twin modeling showed significant genetic effects on overall depressive symptoms (55% variance), shared environment effects on NA (36%) and PA (53%), and shared environment effects on smoking initiation (46%) unique from PA. No other familial influences on the individual phenotypes (apart from those accounting for smoking-depression covariance) were significant. Relations of smoking initiation to overall depressive symptoms and IP were influenced by familial (shared environment and/or genetic) factors and nonshared environmental factors. The SF-smoking initiation relation was influenced mostly by familial factors. Only shared environment significantly influenced the association of lower PA and higher NA to smoking initiation. CONCLUSIONS: Relations between each symptom dimension and smoking initiation are of sizeable magnitude in Chinese adolescents. Genetic and environmental factors underlying depression-smoking comorbidity may vary across different depressive symptom dimensions.