Adherence to the Mediterranean diet partially mediates socioeconomic differences in leukocyte LINE-1 methylation: evidence from a cross-sectional study in Italian women

Although previous research demonstrated that socioeconomic status (SES) might affect DNA methylation, social inequalities alone do not completely explain this relationship. We conducted a cross-sectional study on 349 women (Catania, Italy) to investigate whether behaviors might mediate the association between SES and long interspersed nuclear elements (LINE-1) methylation, a surrogate marker of global DNA methylation. Educational level, used as an indicator of SES, and data on behaviors (i.e. diet, smoking habits, physical activity, and weight status) were collected using structured questionnaires. Adherence to Mediterranean diet (MD) was assessed by the Mediterranean Diet Score (MDS). Leukocyte LINE-1 methylation was assessed by pyrosequencing. Mediation analysis was conducted using the procedure described by Preacher and Hayes. Women with high educational level exhibited higher MDS (β = 0.669; 95%CI 0.173–1.165; p < 0.01) and LINE-1 methylation level (β = 0.033; 95%CI 0.022–0.043; p < 0.001) than their less educated counterpart. In line with this, mediation analysis demonstrated a significant indirect effect of high educational level on LINE-1 methylation through the adherence to MD (β = 0.003; 95%CI 0.001–0.006). Specifically, the mediator could account for 9.5% of the total effect. To our knowledge, this is the first study demonstrating the mediating effect of diet in the relationship between SES and DNA methylation. Although these findings should be confirmed by prospective research, they add value to the promotion of healthy dietary habits in social disadvantaged people.