Systemic inflammation linked to physical, cognitive symptoms of depression

Systemic inflammation is associated with symptom-specific rather than generalized effects on depression, suggests a recent study.

A random-effects pooled analysis was conducted, including 15 population-based cohorts and 56,351 individuals aged ≥18 years. The authors measured serum or plasma concentrations of C-reactive protein (CRP) and interleukin-6 (IL-6) at baseline. Using validated self-report measures, they established 24 depressive symptoms in 15 cross-sectional studies. These symptoms were assessed at follow-up (mean 3.2 years) in seven cohorts.

Depressive symptoms prevalence ranged from 1.1 percent (suicidal ideation) to 21.5 percent (sleep problems). Cross-sectional analyses revealed that higher CRP concentrations strongly correlated with an increased risk of experiencing four physical symptoms (ie, changes in appetite, felt everything was an effort, loss of energy, sleep problems) and one cognitive symptom (ie, little interest in doing things).

Such associations persisted after adjustment for sociodemographic variables, behavioural factors, and chronic conditions; in sex- and age-stratified analyses; in longitudinal analyses; when using IL-6 as the inflammatory marker of interest; in depressed individuals; and after excluding chronically ill individuals.

In addition, overall evidence suggested that inflammation was not associated with four emotional symptoms (ie, bothered by things, hopelessness about the future, felt fearful, life had been a failure).

“Future trials exploring anti-inflammatory treatment regimens for depression may benefit from targeting individuals presenting with symptom profiles characterized by distinct inflammation-related physical and cognitive symptoms,” the authors said.