Depressive symptoms and cigarette smoking in twins from the national longitudinal study of adolescent health

Objective: To our knowledge, no prior twin studies have examined genetic and environmental contributions to the association of depressive symptoms and cigarette smoking in adolescence. Design: Genetic and environmental contributions to the covariation of depressive symptoms and cigarette smoking were estimated among 287 monozygotic and 441 dizygotic adolescent twin pairs from the National Longitudinal Study of Adolescent Health. Main outcome measures: Depressive symptoms were measured using an 18-item modified version of the Center for Epidemiologic Studies-Depression Scale (CES-D; Radloff, 1977). Smoking involvement was defined using an ordinal scale based on smoking recency and frequency. Results: Depressive symptoms and smoking were significantly correlated in both males and females. Twin modeling indicated that, in females, the correlation was attributable in part to common genetic factors and in part to environmental factors not shared among twins, or nonshared environment. In males, the correlation between depressive symptoms and smoking was solely attributable to nonshared environment. Conclusions: Nonshared environmental correlations in males and females lend support to a direct causal relationship between depressive symptoms and smoking in adolescence. However, the additional common genetic vulnerability in females suggested that common genetic factors also contribute, particularly among adolescent females.