The factors driving the association between socioeconomic status and colorectal cancer (CRC) screening are not well defined. In this study, we assessed whether two indicators of poor health behaviour mediated the association between socioeconomic status and CRC screening uptake.
Using population-based data from the Australasian Colorectal Cancer Family Registry, we conducted a causal mediation analysis to determine whether smoking and body mass index (BMI) mediated the association between socioeconomic status – as assessed by educational attainment and Index of Relative Socioeconomic Disadvantage (IRSD) – and CRC screening.
Of 2,193 participants, 25% (95%CI: 23.0%-26.7%) reported at least one previous CRC screening event. The odds of screening uptake increased by 10% for each additional year of schooling (OR 1.10, 95%CI: 1.04-1.16), and 9% for each higher IRSD quintile (OR 1.09, 95%CI: 1.01-1.18). We found 13.5% of the association between CRC screening uptake and years of schooling, and 15% of the association with IRSD to be mediated by pack-years of smoking. We found no evidence on the mediation effect of BMI.
Socioeconomic disparities in screening result in poorer people being less protected from CRC incidence and mortality. A better understanding of the complex interactions underlying the current social gradient in CRC screening is needed in order to develop effective interventions to reduce existing disparities and overall burden of CRC. Our findings suggest that low screening uptake may be due, in part, to poorer health behaviour. Interventions focused on health behaviour might be a valid avenue to increase screening in low socioeconomic categories.