Seasonality of birth in patients with mood disorders in Japan

Background: Findings about seasonality of birth in individuals with mood disorders have been inconsistent. Methods: Data were collected from the governmental statistics, the Patient Survey in Japan in 1996. The number of patients with mood disorders was 13,969. We obtained information about each patient’s date of birth, sex, and diagnosis according to ICD-10. Distributions of monthly birth numbers of patients with mood disorders were compared to those of the general population. Results: Birth excess was observed from winter to early-spring in both sexes, compared to births of the general population. The magnitude of the excess was larger in females than in males. Although the same tendencies were observed in patients with bipolar disorder and depressive disorder, the differences were more marked in females. Limitations: Insufficient birth data in the general population before 1940 and hospital diagnosis. Conclusion: Among Japanese patients with mood disorders, there are excess births from winter to early-spring, compared to the general population. This difference is more marked in females than in males.