Does psychological distress and sleep disturbance mediate the link between socioeconomic position and inflammation?

Socioeconomic position is associated with health inequalities. One way of understanding these health disparities is through the role of chronic inflammation, as measured by inflammatory biomarkers, including C-reactive protein (CRP) and fibrinogen. However, it is not yet fully explained how socioeconomic position and inflammation are associated and whether other factors play a mediating role within this relationship. The purpose of this study was to examine the potential mediating role of psychological distress (General Health Questionnaire; GHQ-12), sleep duration (9 hours or more, 7-8 hours, 6-7 hours, 6 hours or less), and sleep quality (very good, fairly good, fairly bad, very bad) in the link between socioeconomic position and inflammation, using the inflammatory biomarkers, CRP and fibrinogen. Methods: Secondary data analysis was completed using Understanding Society: the UK Household Longitudinal Study. Multiple linear and ordinal regression analyses were used to examine the association between socioeconomic position and inflammation, together with using mediation analysis to explore the potential mediating role of psychological distress and sleep quality and duration. A number of relevant covariates were adjusted for within each of the models. Lower educational attainment and household income were both associated with raised concentrations of both CRP and fibrinogen. Higher rates of psychological distress were associated with lower income but associations were not apparent for educational attainment. Psychological distress did not meet the prerequisite conditions to be a possible mediator. There was a significant association between lower educational attainment with sleep duration, Contrary to what was hypothesised, having no qualifications was associated with a greater likelihood of falling into the 9 hours sleep or more category. Similarly, being in the lowest income tertile was associated with very good sleep, compared to the highest income tertile. Sleep quality was a significant mediator in the association between both educational attainment and household income and CRP, although this is an unexpected finding, therefore more research is needed to explore this. The overall findings demonstrate that socioeconomic disadvantage is associated with increased levels of CRP and fibrinogen, sleep quality was shown to have a potential mediating role, although more research is needed to further understand this relationship as it could constitute a type I error. Sleep and psychological distress are potential points of intervention to alleviate health inequalities. These findings also indicate the importance of welfare support to help attenuate inequalities relating to both physical and mental health.