Socioeconomic status as a correlate of plasma inflammatory markers: An association that may be modulated by the Interleukin-6 (-174)G/C promoter polymorphism

ABSTRACTGrowing evidence suggests that socioeconomic attributes of both individuals and communities of residence confer risk for cardiovascular morbidity and mortality. Despite decades of research demonstrating worse health behavior profiles with lower levels of SES, unexplained variance in the association between SES and cardiovascular disease persists. In this study, we examined the association between both individual and community SES and inflammatory mediators relevant to cardiovascular pathophysiology (i.e. interleukin-6 and C-reactive protein) in a diverse sample of healthy community volunteers. We also examined whether a previously identified functional single nucleotide polymorphism on the IL-6 gene (-174 G-C) is associated with IL-6 and CRP in this sample, and whether it moderates any influence of SES on these inflammatory markers. Subjects were middle-aged men and women (m=424, f=427; Caucasian=76.7%, African-American=22.8%) from the Adult Health and Behavior Project. Individual SES was indexed by averaging educational attainment and family income, and community SES was a composite of five variables from the participants' US Census tract of residence. Regression analyses accounting for age, sex, and race showed individual SES to be associated with IL-6 (B=-.126, p < .001) and community SES to predict both IL-6 and CRP (B= -.163, p <.0001, B= -.129, p = .002, respectively). The inverse relationship between community SES and both inflammatory mediators persisted on multivariable adjustment for health behaviors and individual SES (IL-6: B=-.091, p = .028 and CRP: B = -.086, p = .027). The relationship between individual SES and IL-6 did not withstand health behavior adjustment. Genetic analyses on the Caucasian subsample showed GG homozygotes to have lower CRP than participants with any C allele (i.e. GC & CC; t622=2.00, p <.05), but genotype by SES interactions were not significant. In sum, our results show that regardless of individual income, educational attainment, or -174 G-C genotype, mid-life adults living in less advantaged neighborhoods have higher levels of circulating proinflammatory markers than residents of more affluent areas. This inflammation could mediate the association between lower community SES and atherosclerotic cardiovascular morbidity and mortality