C-Reactive Protein and Specific Depression Symptoms Among Older Adults: An Exploratory Investigation of Multi-Plane Networks Using Cross-Sectional Data From NHANES (2017-2020).

Introduction: Studies investigating the association between C-reactive protein (CRP) and depression among older adults have yielded inconsistent results. We suspect that this may be due to varying associations between CRP and particular depression symptom criteria, and we addressed this challenge using network analysis.

Methods: We used cross-sectional data from prepandemic National Health and Nutrition Examination Survey questionnaires (2017-2020) and included a sample of 1698 adults aged 65 years or older. Depression symptoms were assessed using the Patient Health Questionnaire-9. Unregularized Mixed Graphical Models were estimated using the R package mgm before and after adjusting for relevant sociodemographic, clinical, and lifestyle covariates.

Results: In the model with no covariates, the only symptom criterion associated with CRP was "appetite problems." This association remained robust after controlling for all covariates. Although not associated with CRP, other criteria such as "fatigue" and "concentration difficulty" showed associations with important covariates for older adults such as white blood cell count or hemoglobin, respectively.

Discussion: The CRP-related variability in the depression symptom network that we have demonstrated may help explain the reported inconsistencies. The present study stands as exploratory, and future research should focus on applying longitudinal designs and including several other inflammatory proteins and covariates that were not measured in the current network model.