Abstract
Introduction: Health literacy (HL) is a key determinant of health outcomes, particularly among vulnerable populations such as low-income older adults. Limited HL is associated with poor understanding of medication instructions and lower medication adherence, which can compromise therapeutic success. This study aims to assess the levels of HL and medication adherence among low-income older adults and to analyse the relationship between HL, medication adherence, and other determinants. Methods: A cross-sectional study was conducted among low-income older adults in Portugal's Beira and Serra Estrela Region. HL was assessed using the European Health Literacy Survey Questionnaire (HLS-EU-PT), and medication adherence was measured with the Adherence to Treatment Measure (MAT) scale. Descriptive statistics, Spearman correlations, ordinal logistic regression, and linear regression were used to analyse associations between HL, adherence, and sociodemographic and health factors. Results: Of 196 participants, most had problematic or inadequate HL (87.8%). Medication adherence was relatively high (mean = 5.37, SD = 0.54). HL was positively associated with medication adherence (R = 0.260, p < 0.001), education (R = 0.277, p < 0.001), and ability to pay expenses (R = 0.235, p = 0.002) and negatively with age (R = -0.179, p = 0.019), poor health status (R = -0.237, p = 0.002), and difficulty affording medication (R = -0.389, p < 0.001). Completion of the third cycle of primary education predicted higher HL (OR = 1.939, 95% CI: 0.088-3.790, p = 0.040); the ability to pay expenses predicted better adherence (B = 0.101, 95% CI: 0.014-0.187, p = 0.022). Conclusions: Low HL remains a significant barrier among low-income older adults in Portugal, despite generally high medication adherence. Education and financial stability are key determinants to HL and adherence. Interventions should integrate HL promotion with efforts to reduce socioeconomic barriers and support medication management in the vulnerable populations.