Socioeconomic position and C-reactive protein: The role of psychosocial and behavioral factors

Background: C-reactive protein (CRP) is a marker of systemic inflammation and a potential risk factor for cardiovascular disease. Psychosocial stressors and circumstances associated with chronic stress, such as low socioeconomic position (SEP), have been associated with elevated CRP. It is unclear what mediates these relationships. Objective: To evaluate the association between SEP and chronic stress, as indicated by CRP, and determine the contribution of potential psychosocial and behavioral mediators of that relationship. Sample: 3202 participants of the 2003-2006 National Health and Nutrition Examination Survey aged 40+. Methods: Serum CRP levels were assayed using latex-enhanced nephelometry. A cut-off of 0.3 mg/dl CRP was used to designate clinically-elevated levels. SEP was measured using $10,000 categorical increments of income. Potential mediators analyzed included body mass index (BMI), smoking, adequacy of emotional support, availability of instrumental support, and exercise. Results: After adjusting for age, gender, and race/ethnicity, there was a significant inverse association between income and elevated CRP (OR: 0.90, 95% CI: 0.86, 0.95). Smoking was the strongest partial mediator, reducing the log-odds of high CRP by 14.1%. Exercise and adequacy of support also attenuated the association (7.9% and 4.7% reductions, respectively). In stratified analyses, BMI was a partial mediator for women only (10.2% reduction vs. 24.0% increase in men). Among women, the strongest partial mediator was exercise (12.4% reduction) while among men it was smoking (15.4% reduction). Conclusions: Although these results do not completely explain the relationship between income and CRP, they provide insight that could help inform targeted disease prevention efforts.