Initiation of daily smoking and nicotine dependence in schizophrenia and mood disorders

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Abstract

This study replicates, using more refined methodology, the indications of prior studies that patients with schizophrenia show a greater frequency of tobacco smoking than patients with mood disorders. The sample included 66 patients with schizophrenia and 51 patients with a mood disorder who were admitted at a state hospital in Kentucky. The control group included 404 community subjects. Ever daily smoking was studied using logistic regression. Survival analyses of age of onset of daily smoking (AODS) were performed controlling for several variables including education level. Nicotine dependence was measured with a scale. The prevalence of ever and current daily smoking was respectively 92 and 83% for patients with schizophrenia, 78 and 65% for patients with mood disorders, and 47 and 26% for controls. Before the age of 20, the three populations appear to have a similar risk of smoking initiation. However, after the age of 20, the initiation rate of daily smoking for patients with schizophrenia was higher than in patients with a mood disorder, or controls. Among daily smokers, there were no differences in nicotine dependence between patients with schizophrenia and those with a mood disorder. Schizophrenia was associated with a greater probability of ever daily smoking than mood disorders and with higher rates of initiation of daily smoking after 20 years old.

Introduction

Although patients with schizophrenia abuse other substances, nicotine is the drug of choice for these patients. Schizophrenia appears to be associated with a very high prevalence of tobacco smoking (68–92%) all over the world (Dalack et al., 1998, de Leon, 1996). In a state hospital, schizophrenia was associated with twice the risk of smoking compared with other inpatients with severe mental illnesses (de Leon et al., 1995). Schizophrenia also was associated with twice the risk of heavy smoking (defined as more than 30 cigarettes per day) which may be a gross measure of high nicotine addiction (de Leon et al., 1995). As most of the patients with schizophrenia start to smoke before the illness, we have speculated that vulnerability to schizophrenia may be associated with an increased vulnerability to start smoking (de Leon, 1996). In that sense, Freedman et al. (1997) have described a genetic neurophysiological abnormality in patients with schizophrenia, and their relatives, which is temporarily corrected by a high peak of nicotine. This abnormality is associated with a dysfunction of a specific hippocampal nicotine receptor (α7).

Mood disorders also appear to be associated with tobacco smoking. Glassman (1993) described that subjects with a history of major depression have a greater frequency of smoking and experience more difficulty trying to quit. In a female twin study, Kendler et al. (1993) suggested that genetic factors probably influence the liability to both smoking and major depression. The relationship between tobacco smoking and the other major mood disorder, bipolar disorder, has received less attention. A case-control study showed that ever and current daily smoking were more prevalent in bipolar patients than in the normal population even after controlling for other variables (Gonzalez-Pinto et al., 1998).

It appears that tobacco smoking may be more prevalent in schizophrenia than in mood disorders but this has not been well studied. Our prior study, in a Pennsylvania state hospital showed that schizophrenia doubled the risk of smoking and of heavy smoking when compared with other inpatients with severe mental illnesses including mood disorders (de Leon et al., 1995). The study in Pennsylvania included 201 patients with schizophrenia and 123 patients with other mental illnesses. Mood disorders accounted for only one-third (35%) of the 123 patients with other severe mental illness. Diwan et al. (1998) reported a higher prevalence of smoking in schizophrenia compared to mood disorders in a sample of 83 male veterans. In a prior pilot study in a Kentucky state hospital using the the Fagerstrom test for nicotine dependence (FTND) (Fagerstrom et al., 1996), we found a trend of higher nicotine dependence among patients with schizophrenia when compared with mood disorders in 70 consecutively admitted patients (odds ratio (OR) 2.3, 95% confidence interval, CI, was [0.7,7.8]) (Rogers et al., 1997).

This study tries to establish that schizophrenia is more closely associated with smoking behaviors than mood disorders in a psychiatric hospital in Kentucky. In studies with patients with schizophrenia, patients with mood disorders may be better controls than subjects without mental illness since they are also exposed to factors that could influence smoking such as psychiatric medications or exposition to psychiatric treatment settings where too many patients smoke. The methodologies of this study have several advantages over prior studies. First, this study includes a control group from the community. Second, a comparison of smoking initiation rates within particular age groups in patients with schizophrenia, mood disorders, and controls, was conducted through a survival analysis of age of onset of daily smoking (AODS). Third, a validated scale, the FTND (Fagerstrom et al., 1996) was used to measure nicotine dependence in current daily smokers. Unfortunately, the statistical analyses are rather complicated. However, using survival analysis makes it possible to untangle the effects of confounding variables such as age (some subjects may be too young to classify as never smokers since they may start smoking in the future) or education. Education may be a confounding variable since lack of higher education is associated with smoking and is overrepresented in patients with severe mental illness.

Section snippets

Subjects

After a complete description of the study to the subjects, written informed consent was obtained. The subjects included patients who were admitted to Eastern State Hospital (ESH), Lexington, KY, between March 1998 and May 1999. ESH is the main psychiatric hospital for one-third of Kentucky (central and northern areas). Since there are very few psychiatric units in this catchment area, ESH serves as the main acute psychiatric hospital for the severely mentally ill. Attending psychiatrists, who

Comparisons between patients with schizophrenia and controls

After controlling for gender and level of education in the logistic regression, the odds that a patient with schizophrenia ever smoked daily was 10.1 times higher than a control subject (Table 2).

After controlling for gender and level of education, the cumulative hazard curve from patients with schizophrenia was significantly different from controls (log rank χ2=12.2, df=1, p<0.001). The visual inspection of Fig. 1 suggests that the two populations had essentially the same initiation rates

Discussion

The main limitation of this study or any study using self-report to explore past history of smoking is that the self-report was not verified by other sources. There is no reason to suspect that patients had purposefully misreported information. Regarding current history of smoking, none of the current non-smokers had a CO level suggestive of current active smoking. The effect of medication cannot be completely controlled since patients with schizophrenia and mood disorders take different

Conclusions

Schizophrenia was associated with a greater odds of ever daily smoking than mood disorders and with higher rates of initiation of daily smoking. The visual inspection of Fig. 1 suggests an abrupt decrease of the initiation rate in the control population and mood disorders after age 20 while schizophrenic patients continue to have the same initiation rate as in their teens. This is compatible with the idea that some people with vulnerability to schizophrenia become daily smokers later on their

Acknowledgements

This study was partly supported by the grant MH-51380 from the National Institute of Mental Health (JdL) and a National Alliance for Research in Schizophrenia and Depression (NARSAD) Young Investigator Award (TR) and its supplement from the Department of Mental Health and Mental Retardation/Department of Psychiatry University of Kentucky through the University Collaboration Project (TR). Francisco Diaz is Associate Instructor of Statistics at the Universidad Nacional de Colombia. His

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