The Effects of Tobacco Smoking, and Prenatal Tobacco Smoke Exposure, on Risk of Schizophrenia: A Systematic Review and Meta-Analysis.

BACKGROUND: The association between cigarette smoking and schizophrenia is well established. However, up to 90% of people with schizophrenia begin smoking before the onset of their illness; thus, smoking could be an independent risk factor for schizophrenia. Prenatal exposure to maternal cigarette smoke is also associated with psychiatric problems in adolescence. Therefore, our aim was to undertake a systematic review and meta-analysis to explore the effect of smoking, and prenatal smoke exposure, on risk of schizophrenia. METHOD: We systematically searched Medline, EMBASE, PsychInfo, Maternity and Infant Care, and Web of Science (from inception to February 2018) to identify comparative observational studies of the risk of schizophrenia in relation to smoking status. Measures of relative risk (RR) were pooled in a meta-analysis with 95% confidence intervals (CI), using random effects model. RESULTS: Twelve studies (9 cohort, 3 case-control) were included. Odds ratios (OR) and hazard ratios (HR) were pooled together to estimate pooled relative risks and estimates combined in a meta-analysis on an assumption of constant risk over time. Smokers had a significantly increased risk of schizophrenia compared with nonsmokers (RR = 1.99, 95% CI = 1.10% to 3.61%, I2 = 97%, 5 studies). Exposure to prenatal smoke increased the risk of schizophrenia by 29% (95% CI = 1.10% to 1.51%, I2 = 71%, 7 studies). Sensitivity analyses identified no significant differences between the results from studies reporting OR and hazard ratio. CONCLUSIONS: Our findings suggest smoking, and prenatal smoke exposure, may be an independent risk factor for schizophrenia. Care should be taken when inferring causation, given the observational nature of the studies. IMPLICATIONS: In this meta-analysis of 12 studies, smokers had a significantly increased risk of schizophrenia compared with nonsmokers. Exposure to prenatal tobacco smoke also increased the risk of schizophrenia by 29% compared with those with no exposure to prenatal tobacco smoke. Our findings suggest that smoking, and prenatal tobacco smoke exposure, may be independent risk factors for schizophrenia. These results may have important public health implications for decreasing the incidence of schizophrenia. The possibility of a causal link between smoking and schizophrenia warrants further investigation.

Perinatal maternal life events and psychotic experiences in children at twelve years in a birth cohort study.

BACKGROUND: International studies indicate that the median prevalence of psychotic experiences in children is 7%. It has been proposed that environmental stress during pregnancy may affect the neurodevelopment of the foetus and lead to a vulnerability in the child to later stressors and psychopathology. AIM: In this study we explore the relationship between environmental stress during pregnancy and psychotic experiences in children in the general population at 12 years. METHODS: We analysed a birth cohort of 5038 children from the Avon Longitudinal Study of Parents and Children. Environmental stress was measured as life event exposure. Data on life events were collected on women during their pregnancy, whilst psychotic experiences in the offspring were assessed at age 12. RESULTS: There was a weak association between maternal exposure to life events and psychotic experiences at twelve years (crude OR 1.10 95% CI 1.02-1.18) per quartile of life event score. This association was not reduced after adjustment for socio-economic status, family history of schizophrenia, maternal education or birth weight but after adjustment for maternal anxiety and depression and smoking in early pregnancy there was no longer any evidence for an association (OR 1.01 95% CI 0.93-1.10). CONCLUSION: This study provides some evidence to suggest that stressful life events may affect child psychotic experiences through effects on maternal psychopathology, and possibly physiology, during pregnancy.