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There are many studies that have documented the curious phenomenon that schizophrenia is more prevalent in urban, as opposed to rural, areas. The correlation exists even when confounding factors such as a tendency to migrate to urban areas (better medical care) when symptoms manifest, socio-economic status of people in urban vs. rural areas, obstetric complications, etc. are taken into account. For more details on this connection, see Schizophrenia and urban living before age 15.

Some of these studies have documented an increase in general psychosis related to urban birth, not specifically a diagnosis of schizophrenia. Because psychosis can be a symptom of bipolar disorder, this may be a relevant risk factor. For example, a large study of 2548 total adolescents found that those being raised in an urban area (and who were most likely born there) were significantlly more likely to report at least one psychotic experience when compared with adolescents being raised in rural areas (Spauwen et al 2004). The study also reported a small, non-significant increase in mania among adolescents in urban areas. However, very few studies have examined the prevalence of bipolar disorder in urban vs. rural areas, and therefore no association has been identified. One of the few studies that did look at bipolar disorder found no association (Mortenson et al 2003).

However, given the significant overlap between schizophrenia-spectrum disorders and bipolar disorder, and given that psychosis is a symptom of bipolar disorder, we are including urban birth/urban residence during childhood as a very preliminary, possible risk factor for developing affective psychosis. One piece of evidence that there might be a reduced risk for those in rural areas comes from a 2002 study of a homogenous, non-mobile population in rural Ireland (Scully 2002). Over a five-year examination period, in which each new onset case of psychosis was identified and diagnosed according to DSM-IV standards by the same resident/fellow, the authors found that the new-onset cases of schizophrenia, affective psychosis, and bipolar disorder were significantly reduced from what would be expected in that size of population. The reduction was particularly pronounced among females. The authors did caution, however, that the modest number of overall cases in the five year period affected their calculations of reduced incidence.

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Articles identifying a positive correlation between urban birth and schizophrenia (or psychosis in general) have suggested a number of mechanistic factors that might be at play. These include: increased exposure to viruses during pregnancy (although household crowding is not a risk factor for schizophrenia, so this is questionable), increased exposure to toxic substances such as lead or radiation, aggregation of families with genetic susceptibility, and greater social isolation/fragmentation. This last is particularly intriguing, given that schizophrenia and psychotic disorders are less prevalent in developing (as opposed dto industrialized) countries where social familial ties tend to be stronger, and that social networks have been identified as key to recovery from all the axis-I psychiatric disorders - including schizophrenia and bipolar disorder.

Although urban birth and living is not necessarily a risk factor for bipolar disorder, it would certainly not hurt to be aware of your exposure to toxins and other harmful substances in your environment if you do live in an urban area. Likewise, maintaining a strong social support community for yourself and your children can only make your lives healthier.

Scientific Studies:

• Does urbanicity shift the population expression of psychosis? J Psychiatr Res. 2004 Nov-Dec;38(6):613-8.
• Individual and familial risk factors for bipolar affective disorders in Denmark. Arch Gen Psychiatry. 2003 Dec;60(12):1209-15
• First-episode schizophrenia, bipolar disorder and other psychoses in a rural Irish catchment area: incidence and gender in the Cavan-Monaghan study at 5 years. Br J Psychiatry Suppl. 2002 Sep;43:s3-9.
• Obstetric factors, urbanization and psychosis. Schizophr Res. 2000 Jun 16;43(2-3):117-23.
• Urbanization and psychosis: a study of 1942-1978 birth cohorts in The Netherlands. Psychol Med. 1998 Jul;28(4):871-9