Polydipsia and schizophrenia in a psychiatric hospital: a replication study.

A prior study in a US state hospital suggested that schizophrenia, smoking and long hospitalization were associated with polydipsia. This study, in another US hospital, attempts to (1) replicate that schizophrenia and smoking are associated with polydipsia, and (2) rule out that this relationship is partly explained by alcohol and drug use. Both studies have similar methodologies. The second sample included 588 inpatients. Models of variables associated with polydipsia were developed using logistic regression. In the second study, after correcting for other factors, the association between polydipsia and schizophrenia showed a borderline significance, while polydipsia and smoking displayed a significant association. Neither organic brain lesions, nor alcohol or drug use, were associated with polydipsia. An analysis combining both samples showed that: (1) schizophrenia, long hospitalization, smoking and heavy smoking were significantly associated with polydipsia, and (2) male gender and Caucasian race (but not smoking) increased the risk of developing water intoxication in polydipsic patients. These two studies in severely mentally ill patients suggest that the association of polydipsia with schizophrenia, smoking and chronicity is consistent and independent from the definition of polydipsia (by staff, a biological method or the combination of both). Psychiatric medications do not appear to explain most cases of polydipsia in these patients.

Schizophrenia and tobacco smoking: a replication study in another US psychiatric hospital.

A prior study in a US state hospital suggested that schizophrenia is more closely associated with tobacco smoking when compared with other severe mental illnesses. This second study, in a neighborhood hospital, tries to (1) replicate that schizophrenia is associated with smoking and heavy smoking, and (2) rule out that this relationship is explained by substance use. The methodology was very similar to the first study. The sample included 588 inpatients. Logistic regression was used to develop models of variables associated with smoking or heavy smoking. The frequency of current smoking for the total, schizophrenic and non-schizophrenic samples were respectively 71, 75, and 55%. The sequence of frequencies from the highest to lowest was the same as in the first study: male schizophrenic patients, male non-schizophrenic patients, female schizophrenic patients and female non-schizophrenic patients. This second study consistently replicated the relationship between schizophrenia and smoking (after correcting for other variables) including history of alcohol and drug abuse or dependence. Only one of two definitions of heavy smoking showed a significant association with schizophrenia. In summary, these two studies suggest that schizophrenia is strongly associated with smoking. Neither substance use, antipsychotics, nor institutionalism can explain this relationship.