Background. Health literacy (HL) is a multidimensional construct recognized as a key determinant of health outcomes, influencing individuals’ ability to access, understand, and apply health information. However, existing literature predominantly describes associations between HL and health behaviours, while the mechanisms through which HL produces behavioural change, particularly in physical activity, remain insufficiently specified. In addition, the contextual conditions under which these effects operate, weaken, or fail have not been clearly defined. Objective. This narrative review aims to develop a mechanism-based and condition-sensitive conceptual model integrating healthcare, pedagogical, and physical activity perspectives to explain how, why, and under which conditions HL influences health behaviour, with specific reference to physical activity. Materials and Methods. A structured narrative review was conducted using the PubMed, Scopus, and Web of Science databases. Studies published between 2000 and 2025 were selected based on predefined inclusion and exclusion criteria. The analysis followed a theory-driven synthesis approach aimed at identifying causal pathways, mediating processes, and contextual moderators. Results. The synthesis identifies a multilevel mechanism through which HL influences physical activity and health behaviours via cognitive, motivational, and behavioural regulation processes. However, this mechanism is conditional rather than universal: its effectiveness depends on contextual factors such as educational level, socio-economic status, healthcare system complexity, and digital access. HL effects are strengthened in supportive environments, attenuated in complex communication contexts, and may fail in the presence of structural constraints. Conclusions. HL should be conceptualized not only as a determinant but also as a conditional mechanism of behaviour change operating across healthcare, educational, and social systems. The proposed model provides a theoretically grounded framework with defined causal pathways, mediators, and boundary conditions, offering guidance for the design of integrated interventions to improve health outcomes, promote active lifestyles, and reduce health inequalities.
Liguori et al. (Thu,) studied this question.