Insomnia and depressive symptoms are commonly reported by adults and have independently been found to be associated with mortality, though contrasting findings are reported. Given the high comorbidity and interrelatedness between these symptoms, we tested whether insomnia symptoms explain risk of death independent of depressive symptoms. We examined insomnia symptoms and depressive symptoms, in addition to other health and demographic covariates, as predictors of all-cause mortality.
The sample included 15 418 adults aged 51 and older drawn from a nationally representative, population-based study of adults in the United States, the Health and Retirement Study. Cox survival models were used to analyze time to death between the 2002 and 2014 study waves (5 waves). Controlling for health and demographic covariates, in 3 separate models, depressive symptoms and insomnia symptoms were independently and then together considered as risk factors for all-cause mortality (drawn from the National Death Index).
After adjustment for covariates, insomnia symptoms (HR = 1.10, CI:1.07-1.13) and depressive symptoms (HR = 1.14, CI:1.12-1.16) each were associated with a greater hazard of death. When considered together, however, depressive symptoms fully accounted for the association between insomnia symptoms and mortality.
Though their effects are small relative to health and demographic characteristics, both insomnia symptoms and depressive symptoms were associated with a greater hazard of death. Yet depressive symptoms accounted for the insomnia association when both were considered in the model. Screening for depression and providing validated treatments may reduce mortality risk in old adults with depressive symptoms.