According to the article, winter birth was reported to be a risk factor for schizophrenia in 1929. Clinical aspects of patients with schizophrenia born in the winter include paranoia and a more benign course of illness. Additionally, the clinical features associated with winter birth are different from patients with deficit schizophrenia, defined by the presence of negative symptoms, including inability to experience pleasure, lack of interest in socializing, speech deficits, blunted emotional response, poor eye contact, and more severe course of illness. Nondeficit schizophrenia is characterized by symptoms including hallucinations, incoherent thinking, and prominent delusions.
Erick Messias, M.D., M.P.H., of The Johns Hopkins University, Baltimore, Md., and colleagues analyzed published and unpublished data from the northern hemisphere on studies of season of birth with information on schizophrenia and its subtype- deficit or nondeficit. A total of 1,594 patients were included in the nine studies examined.
"This pooled analysis of data from six countries in the northern hemisphere showed a significant association between deficit schizophrenia and summer birth," write the authors. "Information on month of birth only, as opposed to day of birth, was available across studies, and our analyses found an increase in June/July. However, it is likely that a more seasonal pattern would have been apparent with more detailed information."
"Our results support the concept of a double dissociation in deficit vs. nondeficit schizophrenia and the risk factor of season of birth, with the deficit group associated with summer birth and the nondeficit group with winter birth. This difference strongly suggests differences in etiology between the two groups," the researchers write.
"Seasonal variations in infectious agents, sunlight exposure and vitamin D, and the availability of nutrients have been proposed as possible explanations for the seasonality of births in schizophrenia. However, to date, no specific agent has been identified," conclude the authors.
(Arch Gen Psychiatry. 2004;61:985-989. Available post-embargo at archgenpsychiatry.com)
Editor's Note: This study was supported in part by grants from the National Institutes of Health, Rockville, Md.
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