title: Seasonality of schizophrenia births in the Japanese population: increased winter births possibly confined to the north area.
abstract: A number of North American and European studies have observed a higher proportion of winter births in schizophrenia patients. Thus, seasonal fluctuation of unknown environmental factors may affect brain development in ways that alter susceptibility to schizophrenia. Specification of these factors may help elucidate the etiopathological mechanism of the disease, about which little is certain. A small number of studies have investigated this issue in Asian populations, and the findings are not as consistent as those of Western populations. No remarkable excess of winter births has been observed in Japanese or Korean studies, while some studies have reported a significant decrease of summer births. We further investigated the issue in Japanese patients with schizophrenia (n=3927). No significant excess of winter births was observed, but a decrease in the summer births was found in male subjects. This is largely consistent with previous Japanese studies; however, when the subjects were confined to those born in a colder and higher latitude area of Japan (n=1338), a consistent trend for both a winter increase, and a summer decrease, was found. However, the results did not consistently reach statistical significance, possibly due to the lack of statistical power. Environmental factors that correlate with latitude might play a role in the development of the seasonality of births in schizophrenia. Further studies in a larger sample size are required to test these possibilities.
authors.affiliation: Department of Neuropsychiatry, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan.
authors.forename: Mamoru
authors.initials: M
authors.lastname: Tochigi
authors.forename: Takashi
authors.initials: T
authors.lastname: Onai
authors.forename: Kaori
authors.initials: K
authors.lastname: Narita
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hibino
authors.forename: Mark
authors.initials: M
authors.lastname: Rogers
authors.forename: Tadashi
authors.initials: T
authors.lastname: Umekage
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Kohda
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Otani
authors.forename: Ryo
authors.initials: R
authors.lastname: Kanamori
authors.forename: Nobumasa
authors.initials: N
authors.lastname: Kato
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Sasaki
mesh_terms: D002391:Catchment Area, Health; D015331:Cohort Studies; D004777:Environment; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012559:Schizophrenia / Q000453:epidemiology*; D012621:Seasons