A population-based twin study of the genetic and environmental relationship of major depression, regular tobacco use and nicotine dependence

Abstract

Background: Numerous epidemiological studies have reported a positive association between major depression (MD) and regular tobacco use (RU) or nicotine dependence (ND). However, few have used a genetically informative design to assess whether these traits share a common genetic and/or environmental liability.

Method: We assessed MD, RU and ND in same-sex twins from the population-based Swedish Twin Registry. In males, we examined both cigarette use and snus (smokeless tobacco) use. We used structural equation modeling to examine the relationship between MD, RU, and ND given RU.

Results: The results suggest modest correlations between MD and RU, and between MD and ND. In males, the liability shared between MD and RU is solely genetic for both cigarettes and snus, while MD and ND share both genetic and unique environmental influences. The continuation to ND given RU differed considerably between cigarette and snus users. In females, both MD-RU and MD-ND relationships are partially attributable to genetic and unique environmental correlations.

Conclusions: The relationship among MD, RU and ND is at least partially attributable to shared genetic and environmental risk factors. The genetic and environmental correlations between traits are modest. The nature of the shared liability differs by sex, and in males, by the type of tobacco product used. Differences between previous reports and results presented in the current study are suggestive of population differences in how MD and tobacco use inter-relate.

Fig. 1

Saturated trivariate model depicting relationship between major depression, regular tobacco use and nicotine dependence. In this modified version of the causal–contingent–common pathway (CCC) model, the regression path (β) demonstrates that a score on the nicotine dependence scale is contingent on regular tobacco use. A, C and E represent latent additive genetic, common environmental and unique environmental sources of variance influencing the observed traits.

Fig. 2

Best-fitting models for major depression, regular use of cigarettes (RU_C) and cigarette-based nicotine dependence (ND_C) in males (a) and females (b) and for major depression, regular snus use (RU_S) and nicotine dependence derived from snus use (ND_S) in males (c). A and E represent latent additive genetic and unique environmental sources of variance influencing the observed traits.

Fig. 3

Contributions (%) to the total genetic variance of nicotine dependence (ND). ND_C, ND based on cigarette use; ND_S, ND based on snus use; (), ND-specific; (□), shared with regular use; (■), shared with major depression.