This study assessed smoking behavior and level of schizotypy among a sample of healthy first-degree relatives of patients with schizophrenia and healthy non-psychiatric controls without a family history of schizophrenia. To our knowledge, this is the first study to investigate this relationship among relatives of patients with schizophrenia and compare them to a sample of controls without a family history of schizophrenia.
The first aim of this study was to investigate differences in levels of schizotypy and smoking status between relatives and control participants. Interestingly, the two groups did not differ on level of schizotypy. This is in contrast to both our prediction and prior research that has found a higher level of schizotypy in relatives of individuals with schizophrenia (Asarnow et al., 2001
; Kendler et al., 1993
; Maggini and Raballo, 2003
However, the sample consisted entirely of healthy individuals, and the levels of schizotypy overall were modest. Interestingly, SPQ scores of relatives in this sample were similar to or lower than relatives’ SPQ scores reported in several other studies (Vollema et al., 2002
; Yaralian et al., 2000
). Relatives involved in the study were willing to participate and were involved in patient caregiving, and the inclusion of these individuals may have resulted in a biased group of relatives that had fewer schizotypal traits. Alternatively, some researchers explain the lack of difference between these groups as resulting from defensive reporting in schizophrenia patients’ relatives (Calkins et al., 2004
; Chang and Lenzenweger, 2005
). It may be that relatives have a heightened awareness of schizophrenia symptoms, and as a result present themselves as psychologically healthy.
Another interesting finding was the difference in the proportion of smokers across the two groups. Contrary to our prediction and past research, our study showed a greater proportion of smokers in the control group. Past research has suggested that a genetic predisposition to schizophrenia may be linked with a vulnerability to smoking cigarettes (de Leon, 1996
). Furthermore, one previous study found that relatives had higher rates of daily smoking than controls (Lyons et al., 2002
), suggesting that nicotine consumption may be associated with a familial vulnerability to schizophrenia, raising the possibility that family members are at greater risk of smoking due to their genetic predisposition to schizophrenia.
The next aim of this study was to examine the relationship between level of schizotypy and smoking status, as well as determine potential predictors of smoking status. Interestingly, there was a relationship between smoking status and level of schizotypy in the entire sample. Participants who smoked had significantly higher levels of schizotypy when compared to participants who did not smoke. Furthermore, it was determined using logistic regression that level of schizotypy independently predicted whether a participant was a smoker, and that group moderated the relationship between schizotypy and smoking.
These results support past research on the relationship between schizotypy and nicotine. In a study examining the relationship between smoking, schizotypy, and latent inhibition, a significant positive correlation was found between schizotypy and number of cigarettes smoked per day (Allan et al., 1995
). Another study found significantly higher scores on measures of schizotypy for smoking, healthy adults compared to non-smoking, healthy adults (Williams et al., 1996
). Other studies have yielded similar results (Joseph et al., 2003
; Larrison et al., 1999
).Nicotine may have an effect on the biological substrates involved in the subclinical or personality-related symptoms of a schizophrenia-spectrum disorder, and individuals possessing more of these symptoms may be more likely to smoke cigarettes, given the known biochemical effects of nicotine on overt positive and negative symptoms of schizophrenia.
The final aim was to investigate potential differences in the relationship between smoking and schizotypy in relatives and controls. Both correlations and t-tests revealed a relationship between level of schizotypy and smoking status in first-degree relatives, but not in control participants. When relatives were removed from the analyses, the relationship between level of schizotypy and smoking status disappeared, and when the two correlations were compared statistically, it was determined that the relatives displayed a significantly stronger relationship when compared to the control participants. Furthermore, logistic regression analyses revealed that group was a significant moderator in the relationship between schizotypy and smoking, such that this relationship changed significantly as a result of being a relative versus a control participant.
These results are interesting in that although the relatives and controls do not differ on self-reported schizotypy, the relative group does differ from the control group in that some of them may possess a genetic vulnerability to schizophrenia, given their first-degree relation to an individual with schizophrenia. Although these relatives could not be differentiated from the controls based on self-reported schizotypy, their underlying predisposition to schizophrenia may provide some insight behind the significant relationship between schizotypy and smoking status.
Having a vulnerability to schizophrenia may place an individual at risk for smoking cigarettes, especially if there is a shared genetic vulnerability to both schizophrenia and nicotine dependence. A review of the literature on the genetics underlying nicotine dependence reported that candidate genes likely responsible for nicotine metabolism may also be related to schizophrenia (Yoshimasu and Kiyohara, 2003
). This underlying vulnerability could explain the association between schizotypy and smoking status among first-degree relatives.
Overall, these findings support past research that has demonstrated a link between higher levels of schizotypy and being a cigarette smoker. However, to the authors’ knowledge, this is the first study to date to demonstrate a stronger relationship between schizotypy and smoking status in relatives when compared to control participants. Although relatives did not display a greater amount of schizotypal traits or a greater likelihood of being cigarette smokers, the interaction between reported schizotypy and being a first-degree relative of an individual with schizophrenia may put them at increased risk of being a cigarette smoker.
There are many implications of these findings. Although this study did not find a higher level of schizotypy in these first-degree relatives, it has been shown that schizotypal features typically occur more frequently in relatives of individuals with schizophrenia. Furthermore, given this current result of a relationship between schizotypy and cigarette smoking in individuals with a genetic vulnerability to schizophrenia, it could be assumed that relatives are at greater risk of becoming cigarette smokers. Engaging in cigarette smoking puts these relatives at risk for the increased morbidity and mortality that results from smoking cigarettes. Not only do these findings present important conclusions about nicotine use and schizotypy in relatives of individuals with schizophrenia, they also present potential targets for future public health and psychiatric research.
Several methodological limitations should be considered when interpreting these results. First, this sample of urban, predominantly African American participants may not be representative of broader populations. Second, as suggested previously, the sample of relatives may have been composed of a particularly healthy group of individuals in terms of the level of schizotypy, due to the study’s exclusionary criteria and the fact that meaningful levels of schizotypy (e.g., prominent suspiciousness, social withdrawal) may deter participation in research. Future studies may consider selecting a larger and more heterogeneous group of relatives.
Despite these limitations, this is the first study to date to demonstrate a relationship between schizotypy and smoking status in a sample of participants that included first-degree relatives of individuals with schizophrenia. Future directions in this area include comparing more heterogeneous groups of relative and control participants on these important measures and finding more support for this relationship.