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ABSTRACT
Chronotypes are classified as morning, evening, or intermediate, but there are reports of a bimodal type. This study was undertaken to describe the characteristics of the bimodal chronotype and to explore relationships between the bimodal type and psychiatric disorders, fatigue, and quality of life. A total of 2389 subjects from a Korean national epidemiological survey of psychiatric disorders responded during face-to-face interviews. The Korean Composite International Diagnostic Interview was used to diagnose psychiatric disorders, and the Composite Scale of Morningness was used to assess chronotypes. Among intermediate-type subjects, those with a positive bimodal index were classified as bimodal type. In the present study, the proportions of bimodal, morning, intermediate, and evening types were 4.8%, 10.8%, 73.3%, and 11.1%, respectively. Distributions of sociodemographic variables were similar for the bimodal and intermediate types. After controlling for sociodemographic variables, any mood disorder and major depressive disorder were found to be significantly more associated with the bimodal type than the morning type, and dysthymic disorder was significantly more associated with the bimodal type than the intermediate type. For quality-of-life domains, moderate or extreme pain/discomfort was complained about more by subjects with the bimodal type than other types. In summary, the study shows chronotypes differ with respect to their relationships with mood disorder and quality of life. Before the bimodal type is classified as a clinically valid type, further investigations are needed to examine its psychological, physiological, and genetic characteristics.
Declaration of interest
The authors declare that they have no competing interests.