Depressive Symptoms and Metabolic Syndrome: Is Inflammation the Underlying Link?

Background: Behavioral alterations, including depression, are frequent in individuals with the metabolic syndrome (MetS). Recent findings suggest that chronic activation of innate immunity might be involved. The objective of this study was to examine the relationship between MetS and depressive symptoms and to elucidate the involvement of inflammation in this relationship. Methods: Participants were 323 male twins, with and without MetS and free of symptomatic cardiovascular disease, drawn from the Vietnam Era Twin Registry. Depressive symptoms were measured with the Beck Depression Inventory (BDI). Inflammatory status was assessed using C-reactive protein (CRP) and interleukin-6 (IL-6); twins with both CRP and IL-6 levels above the median were classified as having an elevated inflammatory status. Factor analysis was performed on individual BDI items to extract specific symptom dimensions (neurovegetative, mood, affective-cognitive). Results: Subjects with MetS had more depressive symptoms than those without. Depressive symptoms with neurovegetative features were more common and more robustly associated with MetS. Both the BDI total score and each symptom subscore were associated with inflammatory biomarkers. After adjusting for age, education, and smoking status, the MetS was significantly associated with the BDI total score and the neurovegetative score. After further adjusting for inflammation, the coefficient for MetS decreased somewhat but remained statistically significant for the BDI neurovegetative subscore. When controlling for the MetS, inflammation remained significantly associated with the BDI mood subscore. Conclusions: The MetS is associated with higher depressive symptomatology characterized primarily by neurovegetative features. Inflammation is one determinant of depressive symptoms in individuals with MetS.