Lifetime experiences of hypomanic symptoms are associated with delayed and irregular sleep-wake cycle and seasonality in non-clinical adult samples

Objectives Disturbances of the sleep-wake cycle and seasonality have been reported in patients with bipolar disorder (BD). Considering that BD seems to be a spectrum condition in terms of clinical and biological characteristics, circadian and seasonal rhythm related to BD could be detected in non-clinical individuals with subthreshold bipolarity. The aim of this study was to screen past hypomanic symptoms in non-clinical samples and investigate their association with deviated sleep-wake cycle and seasonality. Methods Lifetime history of hypomanic symptoms was assessed with the Hypomania Checklist-32 (HCL-32). Circadian preference, variability of sleep-wake time and seasonal changes in mood and behavior were evaluated on a lifetime-basis in non-clinical adult samples (n = 313), using the Composite Scale of Morningness (CSM), the Sleep Timing Questionnaire (STQ), and the Seasonal Pattern Assessment Questionnaire (SPAQ). Results Two subdomains of hypomanic symptoms were identified through factor analysis of HCL-32, i.e., "active/elated" factor and "irritable/risk-taking" factor. The HCL-32 total score (p < 0.001) and the "active/elated" factor score (p = 0.028) were weakly correlated only with seasonality, whereas the "irritable/risk- taking" factor score was associated not only with seasonality (p < 0.001), but also with evening preference (p < 0.001) and irregularity of sleep-wake times (p = 0.001 ~ 0.011). Conclusion Circadian and seasonal characteristics related to BD are also associated with a past history of hypomanic symptoms in non-clinical samples, especially "irritable/risk- taking" symptoms, suggesting the existence of subclinical presentation of BD and their biological traits.