Changes in pro-inflammatory cytokine levels and late-life depression: A two year population based longitudinal study

Longitudinal associations of cytokine levels with depression are unclear. This study aimed to investigate cross-sectional and prospective associations between five serum pro-inflammatory cytokine levels and late-life depression. 732 Korean people aged 65+ were evaluated at baseline. Of 631 without depression (Geriatric Mental State schedule) at baseline, 521 (83%) were followed over a 2 year period and incident depression was ascertained. Serum tumor necrosis factor-α, interleukin (IL)-1α, IL-1β, IL-6, and IL-8 levels were assayed at both baseline and follow-up. Associations between cytokine levels and depressive status were evaluated using linear regression models, considering potential covariates (demographics, cognitive function, disability, lifestyle factors, and vascular risk factors) and applying Bonferroni corrections. Prevalent depression at baseline was significantly associated with higher contemporaneous levels of IL-1β and IL-8, independent of relevant covariates and after applying Bonferroni corrections. In the analyses of the five cytokine levels in combination, independent associations were found between prevalent depression and increased numbers of cytokines at higher levels at baseline. Incident depression was significantly associated with increases in IL-1β, IL-6, and IL-8 levels during the follow-up independent of relevant covariates and after applying Bonferroni corrections. In combination analyses, incident depression was independently associated with higher numbers of cytokines showing increasing levels over the same follow-up period. However, incident depression was not predicted by higher baseline pro-inflammatory cytokine levels in any analysis. Our findings suggest that depression might affect serum cytokines alterations and lead to inflammatory processes in late-life.