Evidence of a causal relationship between Smoking Tobacco and Schizophrenia Spectrum Disorders
- 1Queensland Centre for Mental Health Research, Australia
- 2Faculty of Medicine, The University of Queensland, Australia
- 3Metro North Hospital and Health Service, Australia
- 4Faculty of Medicine, University of Turku, Finland
- 5Center for Life Course Health Research, Faculty of Medicine, University of Oulu, Finland
- 6Medical Research Center Oulu, University of Oulu, Finland
There has been emerging evidence of an association between tobacco smoking and schizophrenia spectrum disorders. Two meta-analyses have reported that people who smoke tobacco have an approximately twofold increased risk of incident schizophrenia or psychosis, even after adjusting for confounding factors. This study aimed to critically appraise the research which has examined the association between tobacco smoking and schizophrenia spectrum disorders against the Bradford Hill criteria for causality, to determine the strength of the evidence for a causal relationship. Eight longitudinal studies (seven cohort studies and one case control study) were identified which examined tobacco smoking as an exposure and psychosis as an outcome. All seven cohort studies were assessed as being of high quality using the Newcastle-Ottawa Scale. Six of the eight studies found a statistically significant positive association between tobacco smoking and onset of schizophrenia spectrum disorder. These studies reported a consistent association with a moderate to large effect size and a dose response relationship. The studies adjusted for multiple potential confounders including age, sex, socioeconomic status, shared genetic risk, prodromal symptoms and comorbid cannabis and other substance use. The studies did not adjust for exposure to childhood trauma or prenatal tobacco. There was substantial though inconclusive evidence supporting a causal relationship between tobacco smoking and increased risk of schizophrenia spectrum disorders. If a causal relationship does exist, nicotine is most likely responsible for this association. This raises serious public health concerns about the increasing use of e-cigarettes and other products, particularly by adolescents whose nicotine use may increase their risk of schizophrenia spectrum disorders. Research is urgently needed to examine the association between e-cigarette use and incident psychosis, particularly in adolescents and young adults.
Keywords: Schizophrenia, psychosis, Nicotine, Smoking, Causal, Association, e-cigaertte
Received: 07 Sep 2018;
Accepted: 30 Oct 2018.
Edited by:David J. Castle, The University of Melbourne, Australia
Reviewed by:Boris B. Quednow, University of Zurich, Switzerland
Peter Bosanac, St Vincent's Hospital (Melbourne), Australia
Copyright: © 2018 Scott, Matuschka, Niemelä, Miettunen, Emmerson and Mustonen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Prof. James G. Scott, Queensland Centre for Mental Health Research, Wacol, QLD 4076, Queensland, Australia, firstname.lastname@example.org