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.