Adult socioeconomic position, C-reactive protein and interleukin-6 in the Whitehall II prospective study

Background Prior studies on the association of inflammatory markers, such as C-reactive protein (CRP) and interleukin-6 (IL-6), with socioeconomic position (SEP) have been cross-sectional. Thus, the question of whether socioeconomic differences in CRP and IL-6 change over time remains unanswered. We examined the relationship between SEP and changes over 12 years in CRP and IL-6. Methods Data were for 4,750 middle-aged (mean 49.0 years, SD 5.9) civil servants from phases 3 and 7 of the Whitehall II study. Adult SEP was based on last known Civil Service employment grade. Covariates included sociodemographics, behavioural and biological risk factors, presence of diseases/illnesses, prescribed medications, work-related factors, labour market status and early life factors. Results Steep socioeconomic gradients observed at Phase 3 (p < 0.001) persisted in both CRP and IL-6 12 years later after adjustment for other risk factors. Adjustment for behavioural (diet and smoking), biological (mainly body mass index and total : HDL cholesterol ratio) and early life factors resulted in considerable attenuation but the inverse socioeconomic gradients remained statistically significant. Although CRP and IL-6 concentrations increased substantially over the 12-year period at every level of SEP, CRP and IL-6 did not change differentially according to SEP. Conclusion Despite overall increases in CRP and IL6, relative differences by SEP remained unchanged so that socioeconomic gradients in both sexes persisted over the period observed.