Research report
Actigraphic predictors of the depressive state in students with no psychiatric disorders

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Abstract

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.

Introduction

Mild or moderate depressive state has been defined epidemiologically by several questionnaire surveys (Wells et al., 1989, Judd et al., 1997, Broadhead et al., 1990). The cutoff values for the scores in these questionnaires should be decided by the ethnicity or country based on the results of non-biased epidemiological studies.

Several studies have indicated an association between insomnia and the depressive state, and individuals with depressive symptoms have been reported to show lower levels of physical activity (Mendlowicz et al., 1999). The prevalence of depressive symptoms in Japan is about 4% at the workplace, and extremely high among university students (Iwata and Buka, 2002).

Depressive symptoms are generally reported subjectively, and the duration of sleep can be objectively measured using physiological methods, such as polysomnography or accelerometry (Rechstaffen and Kales, 1968, Acebo et al., 1999). In recent years, wrist actigraphy has been increasingly used to assess the status of sleep and activity in clinical patients and in the general population. There is evidence suggesting that wrist actigraphy can be used to study sleep patterns and psychomotor disturbances in cases of depression (Foster and Kupfer, 1975, Teicher, 1995). Wrist actigraphy has recently become less expensive (Tryon, 1991, Sadeh et al., 1995), and although it is sometimes intrusive, storage of data is relatively easy as compared with that during sleep polygraphy.

We hypothesized that actigraphy could be used to monitor mood disturbances based on the duration of sleep and physical activity levels. To test this hypothesis, we examined whether the depressive state was associated with actigraph-monitored daytime activity levels (DALs) and total sleep time (TST) in university students.

Section snippets

Study subjects

The students who attended the clinical practice course were recruited. Written informed consent was obtained from all the participants. The participants comprised of 105 individuals ranging in age from 22 to 31 years (mean age, 24.1 years (SD, 1.8); 74 men and 31 women), who had no psychiatric disorders.

Procedures

The subjects were continuously monitored for 4 days, except during heavy exercise and bathing, which affect the accelerator. Sleep and wakefulness data were acquired with an Actiwatch® (Mini

Data analysis

The objective of the statistical analysis was to check the association between the actigraphic parameters and the depressive state as assessed by the questionnaire survey, by determining the partial correlation coefficient after controlling for age. A stratified analysis by sex was also conducted. Furthermore, a multiple regression analysis was conducted to check the contribution of the depressive state, sex, age, and DAL to sleep.

Results

Our analysis results revealed that 24.3% of the students exhibited a mild depressive state and 12.6% of the students exhibited a moderate depressive state. Sex difference in the frequency of distribution could not be observed. There was no difference in this distribution of the severity of the depressive state between the sexes (Table 1). A significant association was noted between the CES-D and TST, but only in females (r =  0.49, n = 28). There was no significant association between the TST and

Discussion

The results of this investigation suggest that the daytime activity level as assessed by wrist actigraphy cannot be used as an index of the depressive state even in university students. The present observation is not consistent with previous reports of the inverse association between daytime activity and the severity of the depressive state (Teicher, 1995). Other investigators have also reported significant inverse correlations between activity levels as assessed by activity monitors and the

Acknowledgements

This study was supported by the members in the Department of Hygiene and Public Health, Nippon Medical School, Japan.

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