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Background: Research investigating the link between depression and inflammation has yielded inconsistent results. Given that depression is a heterogeneous condition in which symptoms inter-correlate only moderately, we tested whether prior inconsistencies derive from specific relations between individual depressive symptoms and inflammatory markers.
Methods: We used data from 2321 participants of the Netherlands Study of Depression and Anxiety (NESDA) to estimate six regularized partial correlation network models that displayed relationships between inflammatory markers C-reactive protein (CRP), interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α); 28 depressive symptoms; and sex, age, body mass index (BMI), exercise, smoking, alcohol, and chronic diseases as covariates.
Results: When adjusted for covariates, the IDS sum-score was uniquely associated with IL-6 but not with CRP or TNF-α; CRP and IL-6 were related to BMI; all markers were associated with sex. When modeling 9 DSM-5 MDD criteria and CRP as a replication of Jokela and colleagues (2016), CRP was associated with trouble sleeping, energy level, BMI, and sex. In a final model with all 28 individual symptoms, depression and inflammation were unrelated; CRP was associated with BMI and sex; IL-6 with BMI and age; and TNF-α with chronic diseases.
Conclusion: We provide evidence across numerous models that links between depression and inflammation are largely or completely attenuated, once corrected for demographic and lifestyle covariates. Links survived between the IDS sum-score and IL-6, as well as between the DSM-5 MDD criteria sleep problems and energy level and CRP.
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