Is Schizophrenia a Downside Of Urban Life?

Everybody knows that city living can have its drawbacks—among them noise, pollution, and crime. Now new research has added one more item to that list—heightened risk of schizophrenia.

Preben Mortensen, M.D., a professor of psychiatry at Aarhus University in Taasingegade, Denmark, and colleagues have found the more time a person spends before the age of 15 in an urban area, the higher his or her risk of developing schizophrenia. Mortensen reported this provocative finding at the Ninth International Congress for Schizophrenia Research, which was held in Colorado Springs recently.

Then Jim Van Os, M.D., Ph.D., a professor of psychiatry at Maastricht University in the Netherlands, and his coworkers found a link between city living and DSM-defined psychosis. They also found that while urban environment and familial risk for schizophrenia increased the risk for the illness independently of each other, the effect of city life was much larger on persons who also had the familial risk. These results too were reported at the congress.

But why might living in the city put a person at heightened risk for schizophrenia? Greater exposure to infectious agents is one possibility. As Mortensen and his team found, adolescents who move around a lot between the ages of 13 and 15 are in greater danger of developing schizophrenia than are adolescents of the same age who stay put. “It may be due to being exposed to new reservoirs of infection,” he suggested. Another factor that he suspects is traffic pollution.

And how about the psychological stresses that accrue from city living? Could they be the mediator between city living and schizophrenia risk? It’s possible, several different lines of research suggest.

For instance, Van Os and his colleagues interviewed 80 boys who were hearing “voices” about the adverse events in their lives and followed them for four years. At the end of that time, 13 of the boys had developed delusions that led to a diagnosis of schizophrenia. The researchers found that the 13 boys who had developed schizophrenia had experienced significantly more adverse life events by the start of the study than had the other boys.

In fact, there is reason to think that persons who develop schizophrenia are especially sensitive to stress, and if that is the case, then the wear-and-tear of city life might prove to be especially hard on them.

For example, Van Os and his team measured stress sensitivity—that is, reactions to daily life situations—in schizophrenia patients, their relatives, and control subjects. They found a dose-response relationship—the greatest stress sensitivity in schizophrenia patients, the next most in their relatives, and the least in the controls.

It was also reported at the congress that W.P. Horan, Ph.D., a postdoctoral research fellow at the University of California at Los Angeles, and coworkers found that while the lives of recent-onset schizophrenia patients appear to be more uneventful than those of healthy persons, they have difficulty handling the stresses that come their way.

Discrimination, in fact, might be one type of stressor that could trigger schizophrenia in certain city dwellers. As Van Os pointed out, ethnic minorities in Europe have a higher rate of schizophrenia than do the ethnic majorities, which might be due to discrimination. In fact, he and his colleagues interviewed ethnic minority subjects about discrimination, then followed them over time to see which ones developed schizophrenia. The researchers found a link between having been discriminated against and acquiring schizophrenia.

Robin Murray, M.D., a professor of psychiatry at the Institute of Psychiatry and Maudsley Hospital in London, and colleagues also reported an interesting study at the congress that suggests that discrimination might predispose ethnic minorities in cities to schizophrenia. They studied an ethnic minority population in 15 South London neighborhoods for 10 years. During this time, they found, the minority population decreased progressively in the neighborhoods, while the incidence of schizophrenia in the population increased significantly.

As a result of this finding, they hypothesized that as minorities became a smaller proportion of the population, they may have suffered more discrimination, which resulted in considerably more stress. This added stress may have made them more vulnerable to schizophrenia.

How discrimination or other psychological stresses might set off schizophrenia could be by creating a dysregulation of dopamine in the brain. Shitsij Kapur, M.D., Ph.D., an associate professor of psychiatry at the University of Toronto, voiced this suspicion at the congress. Rats exposed to repeated stressful episodes developed lasting dopamine dysregulation in their brains.

Even with all these explanations, however, the means by which city life appears to underlie schizophrenia remain mysterious. Or as Thomas McGlashan, M.D., a professor of psychiatry at Yale University and a schizophrenia scientist, commented at the congress: “These are fascinating studies; they lead to many speculations.” ▪