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09-08-2010 | Mental health | Article

Smoking may delay full onset of schizophrenia


Free abstract

MedWire News: Individuals with schizophrenia who are current or ex-cigarette smokers may be older at the onset of symptoms than their peers who have never smoked, study results show.

Furthermore, the age of initiation of regular smoking among smokers/ ex-smokers was earlier than their age of illness onset, adding to an increasing body of evidence suggesting that smoking might be a protective factor against schizophrenia, say Tao Li (King's College London, UK) and colleagues.

Patients with schizophrenia are not only more likely to smoke, but also smoke more, favor stronger cigarettes, and extract more nicotine from their cigarettes than individuals without schizophrenia, the authors point out in the journal Psychiatry Research.

However, the underlying mechanism governing the relationship between smoking and schizophrenia is still unknown, in particular whether smoking is a risk indicator for the development of the illness, or an attempt at self-medication.

To investigate further, Li and colleagues assessed 230 male Chinese schizophrenia patients regarding smoking status, clinical history, and cognitive function.

Of the patients, 97 (42.2%) were identified as smokers, 19 (8.3%) as ex-smokers, and 114 (49.6%) as never-smokers.

The average age at schizophrenia diagnosis in these groups was 25.4 years among smokers, 24.4 years in ex-smokers, and 20.4 years in those who had never smoked. Thus smokers/ ex-smokers as a combined group had a significantly later onset of schizophrenia than never-smokers.

In addition, average duration of illness was 38.95 months in smokers, 19.32 months in ex-smokers, and 26.27 months in never-smokers, so when combined, the smokers and ex-smokers had a longer duration of illness than never-smokers. Also, a longer duration of illness was significantly associated with a greater severity of nicotine dependence.

Comparing neuropsychological performance among the groups, the researchers found a nominally significant poorer Stroop C test score in ex-smokers than current smokers (meaning that the processing speed in ex-smokers was slower than in smokers). However, there were no other differences in neurocognitive test performance among the three groups.

"Our study indicates that smoking may delay full symptoms onset of schizophrenia," say Li et al, adding that their findings are "in line with previous studies that smoking might be a protective factor for schizophrenia, and might also improve neurocognitive function."

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Andrew Czyzewski

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