Inflammation is associated with future depressive symptoms among older adults

Inflammation has been reliably associated with depression. However, the directionality of this association is poorly understood, with evidence that elevated inflammation may promote and precede the development of depression, as well as arise following its expression. Using data from older adults (N ​= ​1,072, ages 60-73) who participated in the ongoing longitudinal St. Louis Personality and Aging Network (SPAN) study, we examined whether inflammatory markers (interleukin-6: IL-6, C-reactive protein: CRP, and tumor necrosis factor α: TNFα) and depression were prospectively predictive of one another. Fasting serum samples and self-reports of depressive symptoms (Beck Depression Inventory-II) were obtained from participants at 2 sessions approximately 2 years apart. Structural equation models as well as regressions that accounted for a host of potentially confounding covariates and depression at baseline revealed that baseline IL-6 and CRP, but not baseline TNFα were associated with elevated depressive symptoms at the follow-up session (IL-6: β ​= ​0.080, p ​= ​0.036; CRP: β ​= ​0.083, p ​= ​0.03; TNFα: β ​= ​0.039, p ​= ​0.314). However, there was no association between baseline depressive symptoms and follow-up inflammatory markers (βs ​= ​-0.12 to -0.006, all ps ​> ​0.05). Collectively, these data suggest that inflammation prospectively predicts depression, but depression does not predict inflammation in older age. These data add to a growing literature suggesting that inflammatory signaling may plausibly promote the development of depression.