Consistent with previous reports, the point prevalence of smoking in the schizophrenia group of our epidemiologic first-admission sample (51.0% at year 10) was 2.5-fold greater than in the US population (20.9% in 2005).1
However, rates of smoking were just as high in the other diagnostic groups. The present findings underscore the significance of smoking as a public health problem that cuts across psychotic disorders and possibly all severe mental illnesses. There was little change in smoking status among participants with schizophrenia over the 10-year follow-up, and the average cigarette consumption remained stable, although for individual smokers the amount of consumption fluctuated notably over time. Neither smoking status nor amount of consumption was associated with schizophrenia symptoms. However, changes in the letter were linked with changes in depression symptoms.
We did not find evidence of specificity of smoking to schizophrenia relative to other psychotic disorders at any point during the follow-up, although our study had the power of .93 to detect the level of difference reported in a recent meta-analysis that compared schizophrenia with other psychiatric disorders.2
Further examination of smokers suggested that they were not different from nonsmokers in severity of specific symptoms but were more severely ill overall. For instance, at the end of the follow-up, smokers were 43% more likely to be severely ill than nonsmokers. Thus, it appears that reports of elevated smoking rates in schizophrenia may have confounded diagnosis with illness severity. In support of this interpretation, smoking did not show specificity to nonaffective psychosis in a nationally representative study of mental illness in the United States.48
Furthermore, as mentioned in the Introduction, prospective investigations of relations between smoking and schizophrenia produced contradictory results, and cross-sectional studies failed to find consistent associations between smoking and severity of schizophrenia symptoms. On the other hand, smoking status has been linked to illness severity in general psychiatric samples, albeit assessed with proxy measures.4,8,49
For instance, Aguilar et al49
found no clear links between nicotine dependence and schizophrenia symptoms but observed an association between smoking and frequent hospitalizations, an indirect measure of illness severity.
Examination of cigarette consumption among smokers did not support the self-medication hypothesis with regard to schizophrenia symptoms. However, we found that increases in depression were associated with heavier smoking. This observation is consistent with the extensive literature documenting cross-sectional and longitudinal correlations between smoking and depression in other populations.22
It appears that depression may have an etiologic connection with smoking behavior, and mechanisms for this association have been proposed.22,50–52
These data highlight the importance of addressing depression in smoking cessation interventions.
We did not find differences between smokers and nonsmokers in SES and gender composition, although in the general population smoking is more prevalent among men and in lower socioeconomic strata.1
The gender difference was also observed in schizophrenia samples.2
However, the patients in these studies have typically been ill for a long time. In contrast, our cohort was assessed at the time of the first admission and was followed through the early stages of the illness. We expect that gender and SES differences will emerge in our sample with time.
A notable caveat of this study is that the findings should not be generalized to patients who have never suffered from psychosis. With regard to our diagnostic comparisons, it is important to note that the majority of mood disorder patients did not have any psychotic symptoms at the follow-up assessments, yet no diagnostic differences were observed. Furthermore, severity of psychotic symptoms was associated neither with smoking status nor with cigarette consumption. Nevertheless, our conclusions should also be tested in nonpsychotic severely ill patients. The present findings do show that smoking is highly prevalent across psychotic disorders rather than being specific to schizophrenia. Another limitation of the study is that anxiety was not assessed, despite growing evidence of its links to smoking.5,48,53
Cigarette consumption is also associated with substance use. Evaluation of this relationship was beyond the scope of the present study, but it would be very informative to examine the links between substance abuse and smoking over time. Finally, smoking was measured with a single item and was rated on an ordinal scale rather that continuously. This likely limited reliability of the score and probably led to underestimation of the effect sizes.
Despite these limitations, our findings suggest that smoking is especially prevalent among those with severe mental illness, and special intervention efforts should be directed toward this group. It appears that factors contributing to high rates of smoking are likely to be consistent across the diagnostic groups studied here. One factor with potential etiological significance is depression, and it should be addressed specifically in smoking cessation protocols. Importantly, emerging evidence suggests that smoking cessation interventions can be successfully employed in psychiatric populations,54,55
and quitting does not seem to impede recovery from mental illness.56
Hence, provision of these services to severely mentally ill is an imperative.