Background: Insomnia is one of the characteristics of the early depressive state. One-third of university students has a mild depressive state. In this study, we examined whether the depressive state would be correlated with the actigraphic-derived daytime activity levels (DAL) and total sleep time (TST) in students with no psychiatric disorders.
Method: Consenting volunteers were monitored at home for 3-4 days with a wrist actigraph. The DALs for 3 h before noon (DAL-M) and after 13:00 h (DAL-A) were calculated. The states of sleep and wakefulness were judged based on the activity levels, using a special algorithm. On the first day of the recording, the subjects were requested to fill a questionnaire, "Center of Epidemiologic Scale for Depression Scale (CES-D)," to evaluate the severity of their depressive state.
Results: There was a significant correlation between the DAL-M and DAL-A in both males (r=0.52, n=27) and females (r=0.50, n=21). TST was significantly correlated with depressive state only in the females (r=-0.49, n=28). In contrast, there was no significant correlation between the DAL and the severity of the depressive state. By multiple regression analysis, TST was only a good predictor of depressive state.
Conclusion: The results of this investigation suggest that TST could be used as an index of the depressive state. The TST values in this study decreased as the severity of the depressive state increased, which suggests an association between the severity of the depressive state and insufficient sleep.