In this study of youth with BP, 25% have smoked cigarettes. Among subjects with any lifetime history of smoking, nearly half (44%) were daily smokers, of whom nearly half (45%) were heavy smokers (≥10 cigarettes per day). Smoking among COBY subjects is associated with greater age and with markers of psychiatric burden. As compared to subjects in the Never group, subjects in the Ever and Daily groups had significantly greater lifetime prevalence of suicide attempts, physical abuse, conduct disorder, and SUD. Subjects in the Never group differed significantly from those in the other groups in terms of several domains of family psychiatric history. Regression analyses comparing Never subjects to those in the other smoking groups found that age, lifetime SUD, lifetime suicide attempt, and first- and second-degree family history of SUD were most robustly associated with smoking. In a subset of subjects with information regarding parental smoking, this variable was also independently associated with smoking. Compared to Daily smokers without heavy use (<10 cigarettes per day), those with heavy use (≥10 cigarettes per day) had greater lifetime prevalence of SUD and of suicide attempts, and greater depressive severity at intake, although the latter two findings were reduced to near-significance in regression analyses.
This study found that age was significantly and directly associated with smoking. Previous estimates of smoking prevalence among youth similarly vary with age. Less than 10% of 10–11 year-old participants in a Canadian epidemiologic study had ever tried smoking, as compared to approximately one-third of 12–13 year-olds, and half of 16–17 year-olds28
. The equivalent values in the present study were highly similar: 9%, 32%, and 46% for these respective age groups. Recent representative data from the United States indicate that the prevalence of daily smoking is 4.4% among 8th
graders and 8.3% among 10th
). A previous epidemiologic study found that 7% of adolescents 14–18 years old were daily smokers29
. The prevalence of daily smoking at intake in the present study was 11%, despite the younger mean age of subjects as compared
to the above-cited studies. Moroever, 44% of subjects in the present study who had ever smoked were daily smokers at intake, whereas the equivalent figure in the study by Lewinsohn and colleagues was 19%29
. These findings suggest that youth with BP may demonstrate increased prevalence of daily smoking, whereas the lifetime prevalence of ever smoking is similar to that of non-clinical samples. Similarly, others have found that the presence of psychiatric disorders among youth is associated with increased prevalence of heavy smoking but is not associated with increased risk of experimentation17
Cigarette smoking among youth has also been previously associated with depressive symptoms16, 30–32
. Epidemiologic data from older adolescents suggests that smoking is independently associated with incident depression, after controlling for other disorders, and that lifetime major depression at baseline was the only predictor of smoking onset after controlling for other disorders30
. Another epidemiologic study of youth 8–14 years old at intake found that tobacco smoking was a predictor of subsequent depressed mood, but that antecedent depressed mood was not a predictor of smoking initiation31
. Data from the prospective National Longitudinal Study of Adolescent Health indicate that current cigarette smoking at baseline was the strongest predictor of incident high depressive symptoms, conferring a nearly 4-fold risk32
. Finally, depressive disorders among inpatient youth in a psychiatric unit were associated with a 4-fold increased risk of being a current smoker16
. Future prospective studies from the COBY sample will examine whether smoking is predictive of depressive recurrence, and whether the burden of depressive symptoms predicts incident smoking.
The findings of this study suggest that smoking may be independently associated with suicide attempts, and that heavy smoking is more strongly associated with suicide attempts in comparison to non-heavy smoking. The difference in lifetime prevalence of suicide attempts among Never and Ever subjects remained significant after controlling for potential confounds, whereas the difference between Daily and Never subjects was no longer significant. The finding of an association between smoking and suicide attempts replicates previous findings from adults with BP2, 6
. Ostacher and colleagues reported that smoking was independently associated with a two-fold increased risk of lifetime history of a suicide attempt after controlling for potential confounds2
. Oquendo and colleagues examined predictors of incident suicide attempts in a two-year prospective study of 308 patients who had experienced a major depressive episode (21% of the sample had BP)6
. Cigarette smoking was one the three most powerful predictors of suicidal acts, associated with a two-fold increased risk. A study of adolescent psychiatric inpatients found a four-fold risk of suicide attempts among daily smokers as compared to non-daily smokers after controlling for potential confounds33
. Another study found that heavy daily smoking was independently associated with a two-fold increased risk of suicide attempt among adolescent psychiatric inpatients34
. In contrast to the findings regarding suicide attempts, previous studies have either failed to demonstrate a significant association between smoking and suicidal ideation34
, or, as in the present study, have found that the association between suicidal ideation and smoking is confounded by other factors35
Neither present nor previous findings regarding smoking and suicidality address causality; however, the repeated association of these variables by different research groups examining subjects in different age groups and employing different methodologies suggests that this topic merits further examination. Although we attempted to control for potential confounds of the association between smoking and suicide attempts, such as depressive severity and SUD, future prospective studies from COBY will be better able to examine the direction of this association as well as the potential impact of moderators and mediators.
The significant association between smoking and SUD is consistent with previous findings from adults with BP1, 2, 5
. For adolescents in the community, lifetime smoking of any quantity or frequency is associated with increased prevalence of subsequent SUD in young adulthood36
. Similarly, among inpatient youth in a psychiatric unit, SUD were the strongest predictors of being a current smoker16
Contrary to the study’s hypotheses, the lifetime prevalence of psychosis was nearly identical across the three smoking groups. The possibility that this was due to the inclusion of BP-NOS was explored by examining the association between psychosis and smoking among subjects with BP-I only, however between-group differences in psychosis remained non-significant (p=0.99). Two previous studies of adults with BP have found an association between smoking and psychosis1, 4
, however a third study found no association3
. Therefore, the question of whether psychosis is associated with smoking in BP requires further study.
The strength of the association between smoking and conduct disorder was also less than expected. Although the lifetime prevalence of conduct disorder was significantly lower in the Never group as compared to the other groups, the difference was not significant in the regression analyses. In addition, and in contrast to the findings regarding suicide attempts, SUD, and depressive severity, the association between conduct disorder and severity of smoking was non-significant. Family history of conduct disorder was also not significantly associated with smoking. Similarly, there were no significant between-group differences in the prevalence of ADHD or anxiety disorders. A previous study of adults with BP found that the lifetime prevalence of comorbid anxiety disorders is greater among subjects with, versus without, a history of daily smoking (68% vs. 53%), albeit that this difference was no longer significant in multivariate analyses.2
Prospective data are needed in order to clarify the nature of the association of smoking with psychosis, disruptive behavior disorders, and anxiety disorders among BP youth.
These findings must be interpreted in the context of the methodologic limitations of this study. First, this study is based on cross-sectional and retrospective data, which may be subject to recall bias. However, the current sample is being followed longitudinally, and future reports will allow prospective evaluation of the incidence, prevalence, risk factors, and correlates of smoking. Second, the extent of current smoking in the Ever group could not be determined. Smoking frequency in this group may have ranged from infrequent experimentation to regular, but not daily, smoking. Third, family history of smoking was not ascertained in the same method as psychiatric disorders. Therefore, information regarding smoking among non-interviewed parents, siblings, and other relatives was not systematically ascertained. Fourth, detailed information regarding potential peer-group influence on smoking behavior was not collected. Finally, this study cannot provide an estimate of the prevalence of nicotine dependence in this population, as symptoms of dependence are not ascertained systematically in the KSADS.
Taken together, the findings of this study suggest that cigarette smoking is prevalent among youth with BP beginning in childhood, and that daily smoking may be disproportionately prevalent as compared to community samples. Similar to adults with BP, smoking is independently associated with suicide attempts and SUD. Moreover, among daily smokers, heavy smoking may be associated with greater depressive severity, SUD, and suicide attempts. Unfortunately, few youth in psychiatric treatment settings receive smoking cessation treatment15
. The far lower prevalence of daily smoking as compared to adults with BP1
underscores the important opportunity for prevention that exists. Despite the acknowledged limitations of the present study, and pending the availability of prospective data, these findings suggest that further efforts guided toward smoking prevention and cessation among youth with BP are needed.