Depressive symptoms mediate the association between insomnia symptoms and health-related quality of life and synergistically interact with insomnia symptoms in older adults in nursing homes.

Aims: The aim of this study was to elucidate whether depressive symptoms mediate the association between insomnia symptoms and health-related quality of life (HRQOL) and to explore whether insomnia symptoms and depressive symptoms synergistically interact to affect HRQOL among older adults in nursing homes.

Methods: Older adults living in nursing homes (n = 323) completed Athens Insomnia Scale, the 15-item Geriatric Depression Scale, and the 36-item Short Form Health Survey. PROCESS for SPSS was used in the mediation model. Logistic regression analysis was conducted to obtain odds ratios (OR) for insomnia symptoms, depressive symptoms, and HRQOL. The relative excess risk due to interaction, the attributable proportion due to interaction, and the synergy index were assessed.

Results: Insomnia symptoms and depressive symptoms were negatively related to HRQOL. Depressive symptoms mediated the relationship between insomnia symptoms and HRQOL. Compared with the older adults without insomnia symptoms or depressive symptoms, those with only depressive symptoms (OR = 8.36, 95% confidence interval (CI): 3.46-20.18) or insomnia symptoms (OR = 2.24, 95%CI: 1.04-4.83) had a lower HRQOL. Also, the co-presence of insomnia symptoms and depressive symptoms significantly increased the risk of lowering HRQOL (OR = 25.79; 95%CI: 12.72-52.28). The relative excess risk due to interaction, attributable proportion due to interaction, and synergy index were 16.19, 0.63, and 2.88, respectively.

Conclusions: Depressive symptoms may play a mediating role between insomnia symptoms and HRQOL. Comorbid insomnia symptoms and depressive symptoms synergistically interact to affect HRQOL. It is vital to focus on elderly nursing home residents with insomnia symptoms and/or depressive symptoms and to adopt interventions.