Summary: Meta-analysis finds a two-fold increased risk of developing schizophrenia and psychosis amongst those who smoke tobacco. Researchers speculate nicotine is most likely responsible for the link. They suggest future research looks at the link between e-cigarettes and a possible increased risk of psychosis in young adults, the largest consumer group for the products.
Tobacco smokers are at increased risk of psychotic disorders such as schizophrenia, according to University of Queensland researchers.
Their review of eight long-running studies has found strong evidence of an association between smoking and mental illness, which they suggest is most likely caused by nicotine.
Associate Professor James Scott said the findings raised serious concerns about the increasing use of nicotine through e-cigarettes by young adults.
“People who smoke tobacco have an approximately twofold increased risk of developing schizophrenia or psychosis,” Dr Scott said.
“While e-cigarettes reduce some of the harms associated with smoking, governments need to consider their potential to harm the mental health of young people.”
Dr Scott said e-cigarettes were often reported to be safe, and marketing was directed towards young people.
“More research is urgently needed to examine the association between e-cigarette use and psychosis, particularly in adolescents and young adults,” Dr Scott said.
“Until there is a better understanding of the harm of e-cigarettes, it would be safest that liquid nicotine remains illegal to buy in Australia without a prescription.”
James Scott – Frontiers
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Original Research: Open access
“Evidence of a Causal Relationship Between Smoking Tobacco and Schizophrenia Spectrum Disorders”. James G. Scott, Lori Matuschka, Solja Niemelä, Jouko Miettunen, Brett Emmerson and Antti Mustonen.
Frontiers in Psychiatry. doi:10.3389/fpsyt.2018.00607
Evidence of a Causal Relationship Between Smoking Tobacco and Schizophrenia Spectrum Disorders
There has been emerging evidence of an association between tobacco smoking and schizophrenia spectrum disorders (SSD). Two meta-analyses have reported that people who smoke tobacco have an ~2-fold 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 SSD 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 SSD. 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 SSD. 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 SSD. Research is urgently needed to examine the association between e-cigarette use and incident psychosis, particularly in adolescents and young adults.