Seasonality of birth in patients with schizophrenia in Japan

Although most Western studies have found a birth excess during winter or early spring among patients with schizophrenia, this has not been found in Japanese samples. The purpose of the present paper was to investigate this finding using a large Japanese sample. Distributions of monthly birth numbers of patients with schizophrenia were compared to those of the general population. Patients were from the governmental data, numbering 88 788. A significant birth excess during winter to early spring was found in male and female subjects with schizophrenia compared to the general population. There is a significant birth excess during winter to early spring for schizophrenia in Japan. The authors consider that the discrepancy between the current study and the previous Japanese studies was caused by small sample size and selection bias in the previous Japanese studies.