July 10, 2015

expert reaction to tobacco and schizophrenia

It has previously been observed that sufferers of schizophrenia are more likely to be smokers, though mechanisms for this association have been lacking. This is the subject of a paper published in The Lancet Psychiatry, in which the authors report that daily tobacco use is associated with an increased risk of psychosis and an earlier age of onset. A briefing accompanied these Roundup comments.

Prof. Michael Owen, Director of the Institute of Psychological Medicine and Clinical Neurosciences, Cardiff University, said:

“I think that within the constraints of observational epidemiology this study plus the one by Kendler et al (Smoking and Schizophrenia in Population Cohorts of Swedish Women and Men: A Prospective Co-Relative Control Study; Am J Psychiatry, 2015 Jun 5) make a pretty strong case that smoking is of causal relevance to schizophrenia.

“Confounding (including genetic confounding) and reverse causation are very difficult to rule out in observational studies. The finding that SNPs associated with smoking are associated with schizophrenia supports causality and there is hope that combining genetic analyses with longitudinal epidemiological study designs will help untangle some of these issues. The fact is that it is very hard to prove causation without a randomised trial, but there are plenty of good reasons already for targeting public health measures very energetically at the mentally ill.”

Dr Michael Bloomfield, Clinical Lecturer in Psychiatry, MRC Clinical Sciences Centre and University College London, said:

“It has been known for some time that patients who have schizophrenia are more likely to be cigarette smokers than people who do not have schizophrenia. Yet, a definitive explanation why this is the case has been lacking.

“This new study combines previously published scientific data into a statistical analysis which found that smoking cigarettes appears to modestly increase the risk of developing schizophrenia in later life.  There are a number of plausible ways to explain how this may be happening, such as by heavy cigarette smoking increasing the ability to make the chemical dopamine in part of the brain called the striatum, which is in turn thought to play an important role in the development of schizophrenia. However, much more research is needed before scientists can say for certain that smoking definitely increases the risk of schizophrenia since it remains possible that people who would go on to develop schizophrenia are more likely to start smoking.

“Regardless of these findings, there is overwhelming evidence that nicotine use through tobacco smoking is one of the most dangerous drug problems in the world. Anyone who needs help in stopping smoking should speak with their doctor.”

‘Does tobacco use cause psychosis? Systematic review and meta-analysis’ by Gurillo et al. will be published in The Lancet Psychiatry at 00:01 UK time on Friday 10^th July, which is also when the embargo will lift. 

Declared interests

Prof. Owen: No interests to declare

Dr Bloomfield: “I am a member of the Royal College of Psychiatrists, a trainee member of the British Association of Psychopharmacology and a young member of the European College of Neuropsychopharmacology. I conduct research funded by the Medical Research Council and the National Institute of Health Research. I work in medical research at the Medical Research Council and University College London. I work clinically in the National Health Service. I have no other financial interests to declare.”