Individuals born in cities have twice the risk of schizophrenia compared with persons born in rural areas. A family history of schizophrenia is the most important risk factor for this often disabling illness. However, many cases of schizophrenia arise in families without such histories, indicating that environmental factors also play a role in triggering this psychiatric disorder. According to the authors, the offspring of schizophrenic fathers or mothers had a 7 and 9 times higher risk of schizophrenia, respectively, compared with children born to unaffected parents. But two environmental factors -- place and season of birth -- emerged as risk factors for schizophrenia.
The investigators speculate that individuals born in urban centers may be exposed to more infections before birth and during childhood because of more crowded living conditions. Although the exact causes of schizophrenia remain unknown, experts speculate that fetal or pediatric exposure to infection might have an adverse effect on the still-developing brain. Season of birth appeared to have a slight impact on illness risk. According to the researchers, individuals born in February or March had a 10% above-average schizophrenia risk, while those born in August and September had a 10% lower risk. The reasons for this seasonal variation remain.
The New England Journal of Medicine February 25, 1999;340:603-608, 645-647.
COMMENT: Yet one more influence on healthy childhood development. I was born and raised in Chicago and went to kindergarten and post-graduate medical training all within the city limits. I am quite familiar with urban life. The last 15 years I have shifted to a more rural environment and now really do not enjoy time spent in the city. I am not surprised that the urban environment would be linked to abnormalities in psychological health.