(14-09-10) City Living Can Drive You Crazy

By John Gever, Senior Editor, MedPage Today


MedPage Today Action Points
Explain to interested patients that increased social fragmentation in large
cities may partially explain why psychotic disorders are more common in urban
areas.


Note that the study was limited by a lack of data on potentially important
factors such as cannabis use, reliance on administrative records for data, and
some of the data used in the study was relatively crude.

Review
Increased social fragmentation in large cities may partially explain why
psychotic disorders are more common in urban areas, researchers have suggested.

Results from a long-term study of more than 200,000 people in Sweden indicated
that area-level variables largely explained the correlation between urban
residence and increased prevalence of schizophrenia, reported Stanley Zammit,
PhD, of Cardiff University in Wales, and colleagues.

Residence in a city was associated with a 41% greater likelihood of psychosis
compared with rural residents (odds ratio 1.41, 95% CI 1.09 to 1.82), they
wrote in the September issue of Archives of General Psychiatry.
Among the area-level variables examined, social fragmentation at the school
level -- reflected in the proportion of children who were immigrants, changed
cities between the ages of 8 and 16, or were raised in a single-parent
household -- were the most important, they added.

"Our findings highlight the concern that physical integration [in social
settings] alone is not sufficient, but that some of the positive
characteristics traditionally conferred by segregation, such as a localized
sense of safety, cohesion, and community spirit, must also be maintained to
enhance the mental health of individuals within the population," they wrote.

Previous studies of variations in prevalence of psychotic disorders have found
substantially higher rates, per 1,000 population, in cities relative to rural
areas. However, as Zammit and colleagues noted, those studies could not
determine whether cities act as magnets for people with psychotic tendencies or
whether something about the urban environment promotes psychosis.

The new study comes down on the side of the latter.

The study sample was a cohort of Swedish residents born from 1972 to 1977 and
followed through 2003 for diagnoses of schizophrenia or other nonaffective
psychoses recorded in the country's national health registry.

"The association between living in a city and psychosis was attenuated, but
nevertheless persisted, when adjustment was made for individual-level factors,"
Zammit and colleagues wrote. The city-rural odds ratio dropped only to 1.32
(95% CI 1.01 to 1.72) after controlling for such individual characteristics as
gender, family history of schizophrenia, immigrant status, and single-parent
family.

On the other hand, controlling for school- and municipality-level variables
mostly eliminated the relationship between "urbanicity" and psychosis
prevalence (OR 1.10, 95% CI 0.77 to 1.57).

At the school level, these variables included social fragmentation and the
percentages of the population that was foreign-born or economically deprived.
Municipal-level variables were social fragmentation, deprivation, and
population density.

The only one among them that was significantly associated with psychosis
prevalence by itself was school-level social fragmentation (adjusted OR 1.09,
95% CI 1.01 to 1.18).

But for some of these variables, there were significant interactions between
individual and higher-level variables.

For example, Zammit and colleagues wrote, "individuals who were foreign-born
were at a high risk of developing psychosis if they were part of a school group
with very few others who were foreign-born, and this risk decreased if their
school group consisted of a large proportion of foreign-born individuals."

They scored individuals for social fragmentation, with one point for each of
the three possible components. Statistically, for each point of individual
social fragmentation, a 10% increase in the average for that individual's
school decreased the risk of psychosis by 8% (P=0.004).

In other words, similarity of background between individuals and their school-
level peer groups diminishes the risk of psychosis.

Limitations to the study included lack of data on potentially important
factors such as cannabis use, and some of the data used in the study was
relatively crude. For example, Zammit and colleagues noted that area-level
social fragmentation and deprivation are "difficult to measure." The reliance
on administrative records for all study data was also a limitation.

The study was funded by the National Assembly for Wales and Swedish Research
Council for Working Life and Social Research.

The authors declared they had no potential conflicts of interest.

Primary source: Archives of General Psychiatry
Source reference:
Zammit S, et al "Individuals, schools, and neighborhood: a multilevel
longitudinal study of variation in incidence of psychotic disorders" Arch Gen
Psychiatry 2010; 67: 914-922.

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