The tendency for those suffering from a schizophrenic episode to be smokers has been long assumed to be an example of self-medication: Smoking might help counteract stressful symptoms or the side effects of antipsychotic medication.
What if, however, smoking is one of the causes of schizophrenia? That’s a question researchers at King’s College London’s Institute of Psychiatry took on in a study in Lancet Psychiatry.
Results were inconclusive. Researchers state that “daily tobacco use is associated with an increased risk of psychotic disorder and an earlier age at onset of psychotic illness. However, the effect of smoking seems to be modest.” Still, just the suggestion that the causal direction between smoking and schizophrenia might be the reverse of the usual self-medication explanation caused a stir.
The meta-analysis examined 15,000 tobacco users and 273,000 nonusers, comparing their relative rates of psychosis. They found that 57% of those enduring their first episode of psychosis were smokers. They were three times more likely to be smokers than those in the control groups.
Researchers posit that the genes for smoking overlap with those for psychosis and a commentary that accompanied the study agreed. There are 108 separate genetic loci associated with an increased risk of schizophrenia.
“One of these is located in a cluster of genes—CHRNA5, CHRNA3, and CHRNB5—on chromosome 15, and this region is associated with both early age at onset of smoking and heavy smoking,” say the authors of the commentary, Helen L. Alderson and Stephen M. Lawrie of the University of Edinburgh.
The authors also point out, however, that people typically begin smoking in their teens. People are usually about 25 years old when they are hit by a schizophrenic episode.
“Regular smoking is unlikely to take years to exert a psychotogenic effect but, then again, most smoking-related diseases only arise after prolonged exposure,” the commentators write.
Most studies end with “further research is needed” and that seemed to be the main goal for these authors. They took the first step, and want others to follow with large prospective studies.