Combined Effects of Depression and Chronic Disease on the Risk of Mortality: The Korean Longitudinal Study of Aging (2006-2016)

Background: The prevalence of depression is much higher in people with chronic disease than in the general population. Depression exacerbates existing physical conditions, resulting in a higher-than-expected death rate from the physical condition itself. In our aging society, the prevalence of multimorbid patients is expected to increase; the resulting mental problems, especially depression, should be considered. Using a large-scale cohort from the Korean Longitudinal Study of Aging (KLoSA), we analyzed the combined effects of depression and chronic disease on all-cause mortality. Methods: We analyzed 10-year (2006-2016) longitudinal data of 9,819 individuals who took part in the KLoSA, a nationwide survey of people aged 45-79 years. We examined the association between multimorbidity and depression using chi-square test and logistic regression. We used the Cox proportional hazard model to determine the combined effects of multimorbidity and depression on the all-cause mortality risk. Results: During the 10-year follow up, 1,574 people (16.0%) died. The hazard ratio associated with mild depression increased from 1.35 (95% confidence interval [CI], 1.05-1.73) for no chronic disease to 1.25 (95% CI, 0.98-1.60) for 1 chronic disease, and to 2.00 (95% CI, 1.58-2.52) for multimorbidity. The hazard ratio associated with severe depression increased from 1.73 (95% CI, 1.33-2.24) for no chronic disease, to 2.03 (95% CI, 1.60-2.57) for 1 chronic disease, and to 2.94 (95% CI, 2.37-3.65) for multimorbidity. Conclusion: Patients with coexisting multimorbidity and depression are at an increased risk of all-cause mortality than those with chronic disease or depression alone.