Smoking tobacco is responsible for a range of health problems including cancer and now a new research suggests that it could also increase the risk of psychosis.
Published in Lancet Psychiatry and carried out by researchers at King’s College London, the study is possibly among the first studies that looks into the association of smoking tobacco and increased risk of psychosis – particularly schizophrenia.
Previous studies have delved deeper into why people suffering from mental health problems are more likely to take up smoking compared to rest of the population. Some of the possible explanations put forward by researchers include relief from boredom or distress, and self-medication, whereby smoking counteracts the negative symptoms of schizophrenia or the side-effects of antipsychotic medication.
However, researchers argue that if this was the case, then there would have been evidence that rates of smoking would have increased only after an individual had developed psychosis.
To find out a possible association between smoking tobacco and psychosis, researchers at King’s Institute of Psychiatry, Psychology & Neuroscience (IoPPN) conducted a meta-analysis of 61 observational studies comprising almost 15,000 tobacco users and 273,000 non-users. They analysed rates of smoking in people presenting with their first episode of psychosis and found that 57 per cent of these individuals were smokers.
They also found that people with a first episode of psychosis were three times more likely to be smokers than those in the control groups. The researchers also found that daily smokers developed psychotic illness around a year earlier than non-smokers.
Researchers suggest that their findings clearly call into question the self-medication hypothesis by suggesting that smoking may have a causal role in psychosis, alongside other genetic and environmental factors. However, they acknowledge that despite finding an association between smoking and psychosis, the direction of causality is difficult to determine.
Further, in the meta-analysis there were very few studies that controlled the consumption of substances other than tobacco, such as cannabis, which may have had an impact on the results.
Dr James MacCabe, Clinical Senior Lecturer in Psychosis Studies at the IoPPN, King’s College London, said: “While it is always hard to determine the direction of causality, our findings indicate that smoking should be taken seriously as a possible risk factor for developing psychosis, and not dismissed simply as a consequence of the illness.”
It is thought that activity within the brain’s dopamine system might be one explanation of a possible causal link between smoking and psychosis.
Professor Sir Robin Murray, Professor of Psychiatric Research at the IoPPN, King’s College London, said: “Excess dopamine is the best biological explanation we have for psychotic illnesses such as schizophrenia. It is possible that nicotine exposure, by increasing the release of dopamine, causes psychosis to develop.”
Dr Sameer Jauhar, Research Fellow at the IoPPN, King’s College London, said: “Longer-term studies are required to investigate the relationship between daily smoking, sporadic smoking, nicotine dependence and the development of psychotic disorders. In view of the clear benefits of smoking cessation programmes in this population every effort should be made to implement change in smoking habits in this group of patients.”