Depression, Systemic Inflammation, and Prevalent Diabetes: A Counterfactual Mediation Analysis

Area of Science:

• Medical Science
• Public Health
• Epidemiology

Background:

• Depression and diabetes frequently co-occur, suggesting shared underlying mechanisms.
• Chronic low-grade systemic inflammation is a proposed factor linking depression and diabetes.

Purpose of the Study:

• To investigate systemic inflammation as a mediator in the association between depression and prevalent diabetes.
• To quantify the direct and indirect effects of depression on diabetes through inflammation.

Main Methods:

• Analysis of 2015-2018 National Health and Nutrition Examination Survey (NHANES) data (N=7,583).
• Utilized a counterfactual causal mediation approach.
• Assessed depression (Patient Health Questionnaire), systemic inflammation (hs-CRP, NLR, PLR), and diabetes (HbA1c, self-report).

Main Results:

• Depression was associated with 62% greater odds of prevalent diabetes (Total Effect: OR=1.62).
• A significant direct effect of depression on diabetes was observed (NDE: OR=1.60).
• A small but significant indirect effect of depression on diabetes via systemic inflammation was found (NIE: OR=1.02).

Conclusions:

• Systemic inflammation partially mediates the association between depression and prevalent diabetes.
• While inflammation plays a role, other physiological or behavioral factors likely contribute significantly.
• Further investigation into additional mediators is warranted.