Abstract
OBJECTIVES: This study investigated how the mediating effect of health literacy (HL) on the association between income and cancer screening participation varies by age among Korean adults aged 40 years and older, with the aim of identifying the optimal timing for HL interventions. METHODS: Data from 4171 adults aged ≥40 years in the 2023 Korea National Health and Nutrition Examination Survey were analyzed using moderated mediation analysis implemented with the lavaan.survey package, accounting for the complex sampling design. The Johnson-Neyman technique was used to identify age thresholds at which the mediation effect became statistically significant, and the number needed to benefit (NNB) was calculated to estimate the potential efficiency of interventions targeting this pathway. RESULTS: Each 1-quintile increase in income was associated with a 16.0% higher likelihood of undergoing cancer screening (odds ratio=1.16, p<0.001). The mediating effect of HL increased significantly with age (index of moderated mediation=0.000438, p=0.048). Mediation became statistically significant from age 54.2 years (Johnson-Neyman threshold), with the proportion of the total effect mediated rising from 0.1% among adults aged 40-49 years to 8.1% among those aged ≥70 years. The NNB for this pathway indicated substantial intervention efficiency in older adults (NNB=372 for ages ≥70), whereas the mediation effect was not statistically significant in the 50-59 age group. CONCLUSIONS: HL significantly mediated the relationship between income and cancer screening participation from the mid-50s onward, with progressively greater contributions at older ages. These findings support age-differentiated strategies, including structural accessibility improvements for adults in their 40s and early 50s and integrated income-HL interventions for individuals aged ≥55 years. Experimental studies are warranted to confirm these associations.