Adiposity and Smoking Mediate the Relationship Between Depression History and Inflammation Among Young Adults

Background Depression is associated with inflammation, but the mechanisms underlying this association are unclear. We examined adiposity and smoking as potential pathways through which childhood depression may lead to an elevated inflammatory status among young adults. Methods The sample included 294 subjects with histories of depression (probands), 270 never-depressed siblings of probands (high-risk siblings), and 169 controls. C-reactive protein (CRP), interleukin-6 (IL-6), and soluble intercellular adhesion molecule-1 (sICAM-1) were assessed in serum samples. An adiposity score was computed from body mass index and waist circumference. Smoking behavior was evaluated during an interview. Mixed-effects models were used to test whether adiposity and smoking mediate the relationship between depression and inflammation. Results Probands (p = .004), but not siblings (p = .071), had higher levels of sICAM-1 compared to controls. However, depression history and risk status had no direct effects on CRP (ps > .13) or IL-6 (ps > .16). Importantly, adiposity indirectly mediated the effect of group (probands vs. controls; siblings vs. controls) on all three inflammatory markers. Smoking indirectly mediated the effect of group (probands vs. controls; siblings vs. controls) on sICAM-1 only. Conclusions Among young adults, the adverse inflammatory consequences of depression history are significant for sICAM-1. Adiposity and smoking are pathways through which depression can indirectly impact several inflammatory markers, suggesting possible preventive interventions to improve the immunologic and cardiovascular health of depression-prone individuals.