Health-related literacy and preventive behaviours: a critical review of evidence, methodological challenges and recommendations for future research

Health literacy is widely recognized as a relevant determinant of health, yet its actual contribution to preventive health behaviours remains unclear. The available literature is heterogeneous and often inconsistent, particularly when moving from general HL to domain-specific forms of literacy and from intention to actual behavioural uptake. The aim of this research was to critically examine, through an evidence-based and methodological approach, the role of HL in preventive behaviours across three domains: primary prevention through vaccination, secondary prevention through cancer screening, and personalized prevention through genomic testing. The ultimate goal was to identify methodological indications to improve the validity and reliability of research in this field and to better clarify the contribution of literacy to prevention. The study is based on a set of systematic reviews conducted according to PRISMA guidance and focused on the association between literacy-related constructs and preventive outcomes. Specifically, it examined the relationship between HL and vaccine literacy with vaccination intention and uptake, HL and cancer literacy with cancer screening participation, and genomic literacy with genomic testing decisions. Across these domains, particular attention was paid not only to substantive findings but also to the conceptualization and measurement of literacy, the definition of preventive outcomes, and the methodological aspects of the included studies. Overall, the findings suggest that health-related literacy is an important but not sufficient determinant of preventive behaviours. Across the three prevention domains, literacy was more consistently associated with proximal outcomes such as knowledge, understanding, awareness, confidence, and intention than with actual uptake or adherence. In vaccination, both health literacy and vaccine literacy appeared to be more closely related to intention than to real-world vaccination behaviour, which was also shaped by trust, safety perceptions, social influence, and the broader information environment. In cancer screening, the association between literacy and behaviour appeared somewhat more direct, particularly in organized programs, although results were still not fully consistent across cancer types and measurement approaches. In genomic testing, literacy seemed especially relevant to understanding complex information and supporting informed decision-making, but uptake remained strongly influenced by counselling quality, ethical concerns, access pathways, and governance issues. A major conclusion of this work is that the inconsistency of the literature reflects not only contextual differences across preventive behaviours, but also important methodological weaknesses. These include the predominance of cross-sectional studies, heterogeneity in literacy definitions and instruments, limited psychometric robustness of some measures, frequent reliance on self-reported outcomes, and poor distinction between intention and actual behaviour. Taken together, the findings support a shift from viewing literacy as a stand-alone determinant of prevention to understanding it as one component within a broader network of individual, social, organizational, and structural influences. From a public health perspective, the thesis highlights the need for more theory-driven and methodologically rigorous research, as well as for prevention strategies that combine literacy-sensitive communication with health systems that are easier to understand, access, and navigate.