The mediating role of combined lifestyle factors on the relationship between education and gastric cancer in the Stomach cancer Pooling (StoP) Project

Background The causal pathway between high education and reduced risk of gastric cancer (GC) has not been explained. The study aimed at evaluating the mediating role of lifestyle factors on the relationship between education and GC Methods Ten studies with complete data on education and five lifestyle factors (smoking, alcohol drinking, fruit and vegetable intake, processed meat intake and salt consumption) were selected from a consortium of studies on GC including 4349 GC cases and 8441 controls. We created an a priori score based on the five lifestyle factors, and we carried out a counterfactual-based mediation analysis to decompose the total effect of education on GC into natural direct effect and natural indirect effect mediated by the combined lifestyle factors. Effects were expressed as odds ratios (ORs) with a low level of education as the reference category. Results The natural direct and indirect effects of high versus low education were 0.69 (95% CI: 0.62-0.77) and 0.96 (95% CI: 0.95-0.97), respectively, corresponding to a mediated percentage of 10.1% (95% CI: 7.1-15.4%). The mediation effect was limited to men. Conclusions The mediation effect of the combined lifestyle factors on the relationship between education and GC is modest. Other potential pathways explaining that relationship warrants further investigation.