Epidemiology of comorbid tobacco use and schizophrenia: Thinking about risks and protective factors

A meta-analytic review demonstrated that, when compared with the general population, schizophrenia is consistently and strongly associated with current tobacco smoking with a world average odds ratio (OR) of 5.3 (95% confidence interval, CI 4.9-5.7). The world average OR of current smoking appears to combine four possible components: increased smoking initiation in severe mental illnesses (SMIs), increased smoking initiation that is specific to schizophrenia (beyond the SMI effect), decreased smoking cessation in SMIs, and decreased smoking cessation that is specific to schizophrenia (beyond the SMI effect). In a Kentucky study, only the first three of these four respective ORs were significant: OR = 2.8 (CI 2.0-3.8), OR = 1.9 (CI 1.2-2.8), OR = 4.7 (CI 2.9-7.6) and OR = 1.2 (CI 0.68-2.1). Increased smoking initiation in SMI may be multifactorial. Increased smoking initiation that is specific to schizophrenia probably has a genetic component. Decreased smoking cessation in SMIs may be explained by their high nicotine dependence and the lack of availability and limited success of current smoking cessation treatments. The economic and health costs of smoking in the general population are well understood, but they have received little attention in schizophrenia. More knowledge is needed to develop preventive strategies for the risks and protective factors involved in smoking in persons with schizophrenia. In summary, the main objective of this article is to assess the relative importance of these four components of the association between smoking and schizophrenia, the variables affecting them, and what they tell us about risks and protective factors.