Study objective: To examine the association between depression and three subtypes of insomnia, namely, difficulty initiating sleep (DIS), early morning awakening (EMA), and difficulty maintaining sleep (DMS).
Design: Cross-sectional and longitudinal study.
Setting: Community dwellers in Japan.
Participants: Nationally representative samples of adults aged 65 and over (total N=4,997) were selected by a multistage stratified random sampling method in 1999 and were interviewed face-to-face in 1999, 2001, 2003, and 2006. Those who responded to the 3rd survey conducted in 2003 and the 4th survey conducted in 2006 were used in this study.
Measurement and results: Depression was evaluated according to the 11-item short form of the CES-D scale at 2 points in time. Insomnia subtypes were assessed by self-reported measures. A logistic regression was employed to examine the association between insomnia subtypes and the presence of depression, controlling for relevant factors. A cross-sectional analysis based on the 2003 data demonstrated statistically significant odds ratios (ORs) for DIS and EMA. In the longitudinal study, DIS at the time of the 3rd survey was found to be significantly related to the presence of depression at the time of the 4th survey, with an odds ratio (95%CI) of 1.592 (1.012 to 2.504). EMA (OR 1.070; 95% CI, 0.664 to 1.723) and DMS (OR 1.215; 95% CI, 0.860 to 1.716), however, were not found to be significantly related to the presence of depression.
Conclusion: The longitudinal study revealed a statistically significant relationship, controlling for other relevant factors, between DIS and the presence of depression three years later, but not between EMA or DMS and depression. Based on our findings, we recommend that the association between insomnia subtypes and depression be studied longitudinally in clinical settings.
Keywords: Depression; elderly Japanese; insomnia subtypes; longitudinal study.