A new trio of population-based studies suggests that tobacco use may actually increase one's risk for developing schizophrenia, and that higher rates of cigarette smoking in the illness may not be entirely due to self-medication or other illness factors, as previously assumed.

In one study, led by Foundation Scientific Council Member and two-time NARSAD Distinguished Investigator Grantee Kenneth Kendler, M.D., of Virginia Commonwealth University, smoking predicts risk for schizophrenia in two different Swedish samples. The more a person smokes, the greater the risk. In addition, an analysis of smoking behavior in families suggests that the association is at least partially attributable to genetic factors, reports the American Journal of Psychiatry study published June 5th.

A second study, led by Borge Gronne Nordestgaard, M.D., of Copenhagen University Hospital in Denmark, reports an increased risk of schizophrenia in people with a particular genetic abnormality who had smoked tobacco at some point in their lives, but not in never-smokers. The results were published online June 7th in the International Journal of Epidemiology. A third, smaller study, led by James Scott, Ph.D. of the University of Queensland Centre for Clinical Research in Australia, reports that people who started to smoke tobacco at age 15 or earlier were more likely to later have non-affective psychosis (a diagnosis that includes schizophrenia and schizoaffective disorder), have more delusions, and experience hallucinations than those who had never smoked. The results were published May 19th in the Australian and New Zealand Journal of Psychiatry.

"These three studies overall really shift the weight of evidence in favor of a causal relationship between smoking cigarettes and schizophrenia," said three-time NARSAD Grantee Ezra Susser, M.D., Ph.D., of Columbia University, who was not involved in any of the studies. It's too early to say whether smoking is a risk factor with a causal relation to schizophrenia, but at this point there is more evidence for than against it, he continued. "If it stands up, it will be enormously important," Susser continued.

Read more about this research on the Schizophrenia Research Forum.