Objectives
To estimate and compare (1) how social support (SS) acts as a mediator for the association between health literacy (HL) and health outcomes, and (2) how HL acts as a mediator for the association between SS and health outcomes.

Study design
Mediation analyses.

Methods
Data from the Health Literacy Survey 2019 (HLS19) were analyzed including 42,445 participants in 17 European countries. Four mediation models were tested with two health outcomes: self-reported health (SRH) and health-related limitations (Global Activity Limitations Indicator, GALI). In two models, SS was the mediator between HL and SRH and in the other two models HL was the mediator between SS and GALI.

Results
SS is a significant mediator of the association between HL and SRH in all countries and between HL and GALI in eight countries. Up to 25–30 % of the total effect was mediated by SS. In addition, HL is a significant mediator of the association between SS and SRH in 15 countries and between SS and GALI in eight countries. With regard to SRH, SS may be regarded as the more relevant mediator between HL and SRH; whereas for GALI, HL can be considered the mediating factor between SS and GALI, as the proportions mediated were higher in the respective models in most countries.

Conclusions
Both HL and SS may serve as significant mediators in the models of both health measures, but to different extents. Planning interventions to mutually improve SS and HL may help communities improve health.