Smoking could spark serious mental illness - study

Scientists have found another danger of cigarette smoking. Photo / Thinkstock

Chemicals in tobacco may help trigger serious mental illnesses such as schizophrenia, a study suggests.

New research shows that smoking can triple the chances of developing psychosis.

Previously the fact that people with psychotic mental illnesses are more likely to smoke has been put down to non-causal factors, such as obtaining relief from distress or self-medication.

But now scientists believe something in tobacco might actually be responsible, alongside genetic and environmental influences.

"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," said Dr James MacCabe, a member of the team from King's College London.

The researchers analysed data from 61 observational studies involving almost 15,000 tobacco users and 273,000 non-users.

They found that 57 per cent of people treated for a first episode of psychosis were smokers. Psychotic patients were three times more likely to consume tobacco than individuals without severe mental illness.

The study also showed that daily smokers became psychotic around a year earlier than non-smokers.

The scientists, whose findings are reported in The Lancet Psychiatry medical journal, acknowledge that causality is difficult to prove.

One theory is a possible link between smoking and excess dopamine, a brain chemical that plays a role in transmitting nerve signals.

Professor Sir Robin Murray, from the Institute of Psychiatry, Psychology and Neuroscience at King's College, 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."

A proven link has already been found between cannabis use and psychosis in genetically vulnerable people.

Dr Sameer Jauhar, another member of the King's College team, 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 programs in this population, every effort should be made to implement change in smoking habits in this group of patients."

- PAA