Youth depression and inflammation: Cross-sectional network analyses of C-Reactive protein, interleukin-6 and symptoms in a population-based sample.

Background: Inflammation-related proteins constitute a promising avenue in studying biological correlates of major depressive disorder (MDD). However, MDD is a heterogeneous condition - a crucial aspect to be considered in association studies. We examined whether inflammatory proteins are associated with categorical diagnosis, a dimensional total sum-score, and specific depressive symptoms among youths.

Methods: We analyzed data from the 1993 Pelotas Birth Cohort, a population-based study in Brazil that followed individuals up to age 22 years. Categorical psychiatric diagnoses were derived using adapted modules of the Mini International Neuropsychiatric Interview (MINI). Dimensional symptomatology was assessed using the Brazilian Portuguese version of the Center for Epidemiological Studies-Depression Scale-Revised (CESD-R). We estimated network structures that included individual depressive symptoms as measured by CESD-R items, peripheral inflammatory markers (C-Reactive Protein [CRP] and Interleukin-6 [IL-6]), as well as relevant covariates.

Results: We evaluated 2586 participants (mean age = 22.5[SD = 0.33]) There were no associations between concentrations of inflammatory proteins and categorical diagnosis of MDD or with CESD-R total sum-scores. In symptom-specific analysis, CRP and IL-6 were positively connected to somatic and cognitive items.

Discussion: We found cross-sectional connections of two commonly studied inflammatory proteins and specific depressive symptoms. Conducting symptom-specific analyses in relation to biological markers might advance our understanding of the heterogeneity of MDD.