A Longitudinal Analysis of Late Adolescent Co-Morbidity Between Cigarette Use and Mental Health Problems Using the NLSY

Background and Purpose: The prevalence of cigarette use and symptoms of depression and anxiety show high rates of co-morbidity, both undergo rapid onset during adolescence, and both work on the same brain receptors. Because studies both suggest that smoking increases the likelihood of developing depression/anxiety problems and depressed-anxious adolescents are at greater risk for smoking, this study examined the longitudinal progression of the co-occurrence of cigarette use and depression/anxiety problems. The purpose of the study is to understand the stability between and within these problems over time in U.S. adolescents. Because existing research suggests that female adolescents may be at increased risk of becoming heavy smokers, we were also interested in whether co-morbidities differed by gender. Methods: We used the NLSY97 longitudinal study containing a nationally representative sample of U.S. adolescents. The NLSY assesses adolescents' development in several areas; educational, labor market experiences, mental health, alcohol and other drug use, among other factors. NLSY measures of depression/anxiety are available only in waves 4, 6 and 8. Thus the analyses included data from these three waves. A total of 8,544 adolescents (Mean age at wave 4 = 17.9, SD=1.44, 49% female) were included in the analyses. To investigate the co-morbidity between depression/anxiety and cigarette use, latent factors of depression/anxiety and cigarette consumption were constructed at each wave. The depression/anxiety latent factors were based on five items measuring how often participants felt down, depressed, nervous, calm and happy. The cigarette use latent factors were based on two items measuring, in the previous month, the number of days they had smoked and the number of cigarettes smoked per day. Finally, we estimated a three wave Bivariate Autoregressive Cross-Lagged Effect Model to test the conjoint trajectory of depression/anxiety and smoking. The fit of the final model was very good (CFI = 0.948, TLI=0.970 and RMSEA=0.059). Results: Prior depression/anxiety status influenced future depression/anxiety status between waves (0.685, p<0.001; 0.794, p<0.001) and previous cigarette use was a strong predictor of future cigarette use across waves (.925, p<0.001; 912, p<0.001). The model also suggested cross-lagged effects between waves 4 and 6. The greater depression/anxiety problems at wave 4, the more likely adolescents were to use cigarettes in the future (.268, p<0.01).The more cigarette use at wave 4 the more depression/anxiety at wave 6 (0.009, p<0.001). Separate models were tested by gender revealing same patterns between males and females.

Conclusions and Implications: The findings of this study showed that, both mental health and cigarette consumption influence each other during late adolescence. These findings could be explained by two hypotheses. First, adolescents with more depression/anxiety problems would use nicotine to treat their symptoms (self medication hypothesis). Second, common genetic factors may account for both the addiction to nicotine and vulnerability to depression/anxiety problems. Further research is needed to explore in more detail the mechanics of the co-morbidity of depression/anxiety and nicotine addiction. Major implications for prevention and treatment programs include considering both nicotine dependence and depressive-anxious disorders as two factors that jointly affect each other.