Premorbid tobacco smoking is associated with later age at onset in schizophrenia

Rates of cigarette smoking in individuals with schizophrenia well exceed those in the general population and in other mental illnesses. In the present study, we examined the relationship between smoking status, clinical characteristics and cognitive functions in 230 male Chinese schizophrenia patients. They were interviewed by experienced psychiatrists using the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) (SCID-P). Clinical symptoms were rated using the Positive and Negative Syndrome Scale (PANSS), and the Revised Tolerance Questionnaire (RTQ) used to evaluate the severity of nicotine dependence. Nine neuropsychological tests were used to assess cognitive function. We found that never-smokers had a younger age at examination and earlier onset and longer duration of illness than smokers and ex-smokers. The age of initiation of regular smoking in patients was significantly earlier than their age of illness onset. We found that longer duration of illness was significantly associated with higher RTQ scores. Ex-smokers with schizophrenia performed significantly more poorly on the Stroop C test than smokers. The results imply that smoking may affect cognitive function and illness onset time in patients with schizophrenia.