No Significant Association Between Vitamin C Supplements and Frailty in Korean Older Adults: A Cross-Sectional Analysis of the 2018–2019 Korea National Health and Nutrition Examination Survey

Background/Objectives: The association between vitamin C intake and frailty among older adults remains unclear, and evidence from Asian populations is limited. Using nationally representative data, we aimed to examine whether vitamin C supplementation is associated with frailty in Koreans aged ≥65 years. Methods: We analysed 2819 participants from the 2018–2019 Korea National Health and Nutrition Examination Survey. Participants were categorised as non-users of dietary supplements (n = 1517), users of other supplements (n = 1227), and vitamin C-only users (n = 75). Frailty was defined using a modified Fried phenotype comprising five components (weight loss, exhaustion, weakness, slowness, and low physical activity); individuals having ≥3 components were classified as frail. Multivariable logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for frailty by supplement use and total daily vitamin C intake from foods and supplements, adjusting for sociodemographic, lifestyle, and health factors. Results: Compared with non-users (adjusted OR: 0.65, 95% CI: 0.26–1.66) or users of supplements other than vitamin C supplements (adjusted OR: 0.81, 95% CI: 0.26–2.53), vitamin C supplementation was not significantly associated with frailty prevalence. Higher total intake showed a tendency toward lower frailty prevalence in crude analyses, but this was not significant after adjustment (p for trend = 0.120). Conclusions: In this nationally representative study of Korean older adults, vitamin C supplementation was not significantly associated with frailty. These findings contribute to the conflicting evidence on micronutrients and frailty and suggest that broader dietary quality, rather than single-nutrient supplementation, may be more important for healthy ageing.