Smoking 'could cause schizophrenia', say scientists

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Scientists have suggested that smoking may be a risk factor for developing psychotic illnesses like schizophrenia.

People who suffer from psychosis are three times more likely to smoke than the general population, a new analysis of existing data published in the Lancet Psychiatry journal found.

While this association has been noted before, little research has been conducted into whether smoking could actually be a causal factor for psychosis.

Researchers from Kings College London, who conducted an analysis of 61 studies comprising data on 15,000 smokers and 273,000 non-smokers, also found that daily smokers who went on to develop psychosis did so on average a year earlier than smokers who developed the illnesses.

The findings cannot prove causation, and the researchers said that some of the studies they looked at did not take into account possible confounding factors, such as whether smokers were also regular cannabis users, something which is associated with psychotic illness.

However, Dr James McCabe, clinical senior lecturer in psychosis studies at the King’s Institute of Psychiatry, Psychology and Neuroscience (IoPPN) said smoking should be “taken seriously as a possible risk factor” for psychosis and not “dismissed as a consequence of the illness”.

Researchers suggested a possible explanation for the link could be smoking’s impact on levels of the chemical dopamine in the brain, which also plays a role in psychotic illness.

Sir Robin Murray, professor of psychiatric research at the IoPPN 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.”