A team of researchers from University of Queensland have found that tobacco use is associated with an increased risk of psychotic disorders including schizophrenia.
The study titled “Evidence of a Causal Relationship Between Smoking Tobacco and Schizophrenia Spectrum Disorders,” was published in the latest issue of the journal Frontiers in Psychiatry.
Image Credit: Sruilk / Shutterstock
For this study the team looked at eight long term studies and collated the data available to find the evidence that smoking could be linked to mental illnesses. They team suggests that nicotine in tobacco could play a role in these disorders.
According to lead author of the study Associate Professor James Scott this also raises concerns about the rising nicotine use among youngsters in the form of e-cigarettes. He said that those who smoke are at a “two fold” risk of schizophrenia or psychosis as is evident from these studies. He 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. More research is urgently needed to examine the association between e-cigarette use and psychosis, particularly in adolescents and young adults, until then, liquid nicotine should remain illegal for purchase in Australia without a prescription,” Dr Scott said.
The team looked at eight long term cohort studies. They found that six of the eight showed a statistically significant association between tobacco smoking and psychotic disorders or schizophrenic spectrum disorders or SSD. According to authors SSD includes, “schizophrenia, schizophreniform disorder, schizoaffective disorder, delusional disorder, non-affective psychotic disorder, atypical psychosis, psychotic depression, and bipolar mania with psychotic features”. The team adjusted the findings for age, gender, genetic risk, use of other substances such as cannabis, socioeconomic status etc. before coming to the conclusions.
To assess if there was any association, the team used a Bradford Hill Framework which contains nine criteria that can link the exposure to outcome. Of these nine criteria, five were chosen to be highly relevant. All studies were conducted in high income countries. The participants in the studies were followed up for a minimum of 4 years to a maximum of 48 years.
Results showed that there was a six fold rise in risk of schizophrenia in heavy smokers as seen from the strength of association. Only one of the eight studies did not show a causal association between smoking and schizophrenia write the researchers. Overall there was a two-fold rise in risk of schizophrenia among smokers, the researchers write.
The authors of the study explain that there are around 5000 different chemicals in tobacco smoke but nicotine seems to be the main culprit here. There have been studies that have shown that nicotine is capable of altering the signal system of the brain mainly in the “dopaminergic, cholinergic, and glutamatergic neurotransmitter systems,” they explain. This could negatively influence brain maturation in teenagers and young adults. Further this could cause “strengthening of negative emotional changes and alterations in cognitive functioning,” in adolescents they add and this could possibly lead to mental ailments later in life.