Lifetime pathogen burden, inflammatory markers, and depression in community-dwelling older adults

The link between pathogen exposure and mental health has long been hypothesized, but evidence remains limited. We investigated the association of seropositivity to common pathogens and total pathogen burden with depression and mental health and explored the role of mediating inflammatory cytokines. We profiled in 884 participants in the Singapore Longitudinal Ageing Studies, mean (SD) age: 67.9 (8.1) years, their seropositivities for 11 pathogens (CMV, HSV 1, HSV 2, HHV-6, EBV, VZV, RSV, Dengue, Chikungunya, H. Pylori and Plasmodium) and pathogen burden, Geriatric Depression Scale (GDS) score at baseline and 3-4 and 6-8 years follow-up, and baseline Mental Component Score (MCS) of 12-Item Short Form Survey (SF-12). Inflammatory markers included CRP, TNF-α, IL-6, MIP-1α, sgp130, sTNF-RI, sTNF-RII, C3a, and MCP-2. Controlling for age, sex, ethnicity, education, marital status, living alone, and smoking status, high pathogen burden (7 + cumulative infections) compared to low pathogen burden (1-5 cumulative infections) was significantly associated with period prevalence (the highest GDS score from baseline and follow-up measurements) of depressive symptoms (OR = 2.36, 95% CI = 1.05-5.33) and impaired mental health (OR = 2.25, 95% CI = 1.18-4.30). CMV seropositivity and HSV1 seropositivity, which are highly prevalent and most widely studied, were associated with estimated 2-fold increased odds of depression, but only HSV1 seropositivity was significantly associated with depression after adjusting for confounders. Notably, adjusted for confounders, RSV, H. pylori and Plasmodium seropositivity were significantly associated with increased odds, and Dengue seropositivity was associated with unexpectedly deceased odds of depressive symptoms and impaired mental health. The association of pathogen exposure with depression and mental health were at least in parts explained by inflammatory markers. Adding certain inflammatory markers to the models attenuated or weakened the association. Bootstrap method showed that MIP-1α significantly mediated the association between pathogen burden and mental health. In conclusion, lifelong pathogen burden and specific infections are associated with depression and impaired mental health in older adults.