Combined Effects of Pain Interference and Depressive Symptoms on Dementia Incidence: A 36-Month Follow-Up Study

Background: Both pain interference and depressive symptoms have certain effects on dementia, and these are reciprocally related. However, comorbid effects of pain interference and depressive symptoms on dementia have not been examined in detail. Objective: This longitudinal study aimed to examine the combined effects of pain interference and depressive symptoms on the incidence of dementia in community-dwelling elderly individuals. Methods: This prospective cohort study with a 36-month follow-up period included 4,326 community-dwelling elderly individuals without dementia at baseline. Pain interference and depressive symptoms were assessed for every participant at baseline. We collected medical records in the Japanese public health insurance system to identify the incidence of dementia for 36 months. Results: The incidence rates of dementia during the follow-up period in the control, pain-interference, depressive-symptoms, and comorbid group were 3.2%, 6.2%, 7.9%, and 11.3%, respectively. A Cox regression analysis showed that the hazard ratios for the incidence of dementia were 1.85 (95% CI: 1.13-3.03) in the pain interference group, 1.87 (95% CI: 1.27-2.76) in the depressive symptoms group, and 2.20 (95% CI: 1.26-3.84) in the comorbid group, after adjusting for covariates. Conclusion: The coexistence of pain interference and depressive symptoms had a greater effect on the incidence of dementia than either condition alone in community-dwelling elderly individuals. Pain interference and depressive symptoms are known as common comorbid conditions and often form a negative cycle that accelerates the worsening of the individual symptoms of both. Thus, the comorbidity of these conditions may require monitoring for the prevention of dementia.