Impact of multimorbidity and cognitive impairment on depressive symptoms in community-dwelling older adults and their interaction effects

This study aims to evaluate the independent and interactive effects of multimorbidity and cognitive impairment on depressive symptoms among older adults in China. Employing a cross-sectional design, the study collected data from 10,369 individuals aged 65 and above across 35 communities/villages in China. Depressive symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9), cognitive function was evaluated with the Alzheimer's Disease-8 (AD-8) scale, and chronic disease conditions were recorded. The results indicated that older adults with multimorbidity (OR = 2.481, 95% CI: 2.117, 2.908) and those at high risk of cognitive impairment (OR = 5.469, 95% CI: 4.644, 6.441) exhibited a higher likelihood of experiencing depressive symptoms. Further interaction analysis revealed that, after controlling for confounding factors, no significant multiplicative interaction was found between multimorbidity and cognitive impairment (P = 0.581); however, a significant additive interaction effect was observed (OR = 13.809, 95% CI: 11.063, 17.237). These findings suggest that multimorbidity and cognitive impairment are important factors associated with depressive symptoms in older adults, and their combined presence is linked to a substantially increased likelihood of experiencing depressive symptoms compared to either condition alone.