Psychiatric epidemiology in Japan: towards psychological understanding of the etiology of minor psychiatric disorders.

Epidemiological studies of psychiatric disorders using structured interviews and operational diagnostic criteria in a community population are rare in Japan. In our community study with mainly middle-aged people (Kofu Study), the lifetime prevalence of Major Depressive Episode was 19%. The prevalence was about twice as high in women as in men. The prevalence of Major Depressive Episode showed a tendency to increase as the subjects became younger. No sex difference in the lifetime prevalence of Major Depressive Episode was observed among an adolescent population (Gotemba Study), due to the equally high prevalence of this disorder among male adolescents. The figures were 24% for men and 23% for women. In a follow-up study of pregnant women (Kawasaki Study), risk factors of depression during pregnancy and after childbirth are different and, in some instances, reversed. Therefore, we speculate that the combination of psychological risk factors of the onset of depression may differ from one situation to another. Specificity of the combination of risk factors may be more important than single risk factors in the etiology of mild-form depression.