Relationship between health literacy, fruit and vegetable consumption, and dietary supplement use among Korean adults

Ⅰ. Introduction

As interest in health promotion continues to rise, the consumption of dietary supplements (DS) has steadily increased in Korea (Korea Health Functional Food Association, 2025). While their widespread use, accumulating evidence suggests that the health benefits of DS are limited. Meta-analyses and systematic reviews have consistently reported that DS use does not provide significant preventive effects against chronic diseases and, in some cases, may even be associated with adverse health outcomes, including increased mortality (Bjelakovic et al., 2012; Myung et al., 2013; US Preventive Services Task Force, 2022). Despite this scientific skepticism, DS continue to be marketed as essential components of healthy diets, and a considerable proportion of adults use DS as part of their health management strategies.

Previous research has identified heterogeneous patterns of DS use. One pattern, often described as the “healthy user” pattern, characterizes individuals who already engage in health-promoting behaviors, such as having healthy diets and regular physical activity, and use DS as a proactive addition to their healthy lifestyles (Dickinson & MacKay, 2014). In contrast, the “compensatory user” pattern refers to individuals who rely on DS as a means to address perceived inadequacies in their diet (Yan et al., 2025). These divergent patterns indicate that DS use reflects how individuals interpret, evaluate, and act upon health-related information.

Health literacy (HL), defined as the ability to access, understand, appraise, and use information to inform health-related decisions and actions has widely recognized as a key determinant of health behaviors (Sørensen et al., 2012). While HL is associated with diverse health-promoting behaviors, it is also relevant to dietary decision-making, which requires individuals to navigate complex and often conflicting information regarding nutrient sources, dietary recommendations, and commercial health claims (Forray et al., 2023; Ma et al., 2024). Thus, HL is associated with individual dietary choices, including what to eat, how much to eat, and what combinations to eat.

One of the important component of healthy diets is adequate consumption of fruits and vegetables (FV). FV are rich sources of vitamins, minerals, fiber, and phytochemicals, and high intake has been consistently linked to reduced risks of chronic diseases such as obesity, hypertension, cancer, and mortality (Aune et al., 2017). Accordingly, dietary guidelines recommend consuming at least 400–500g of FV per day, preferably in whole food form to prevent non-communicable diseases and micronutrient deficiencies (Ministry of Health and Welfare & The Korean Nutrition Society, 2020; World Health Organization, 2003). Due to the high consumption of salted vegetables, such as kimchi, the dietary guidelines for Koreans recommend a daily FV intake of 500g or more, which is higher than international recommendations (Ministry of Health and Welfare & The Korean Nutrition Society, 2020). In contrast to this whole FV consumption recommendation, reliance on DS as a means of meeting nutritional needs has increased (Korea Health Functional Food Association, 2025). While DS may be beneficial for specific populations, such as folic acid supplementation for pregnant women, whole foods are recognized as superior due to their synergistic matrix of micronutrients and phytochemicals that DS cannot replicate (Liu, 2003). Thus, public health guidelines consistently emphasize a food-first approach, recommending that DS should not be prioritized over whole foods (US Department of Agriculture & US Department of Health and Human Services, 2020). This distinction underscores the importance of understanding whether individuals prioritize whole-food sources, such as FV, or rely on DS as an alternative strategy for nutrient intake.

Existing evidence suggests that higher HL is associated with better diet quality and higher FV consumption (Forray et al., 2023; Ma et al., 2024). From this perspective, individuals with higher HL may be expected to recognize the limited benefits of DS and to prioritize nutrient intake from whole-food sources such as FV. However, it is also possible that higher HL does not necessarily lead to healthier dietary choices, such as adopting a food-first approach. Recent studies have highlighted that, as the nutrition and health information environment becomes increasingly complex and commercially driven, the ability to merely access and understand nutrition information may be insufficient. Instead, greater emphasis has been placed on critical nutrition literacy, defined as the capacity to critically evaluate nutrition-related information and claims (Bedoyan et al., 2021; Guttersrud et al., 2014). In particular, DS market is characterized by aggressive marketing strategies that strongly emphasize health benefits. In this context, individuals are required to possess the ability to critically evaluate such claims in light of established dietary guidelines and scientific evidence.

To our knowledge, the relationship between HL, DS use, and FV intake has not been fully understood. Notably, a meta-analysis reported that higher HL is associated with increased DS use (Intarakamhang & Prasittichok, 2022), whereas another study showed that among DS non-users, greater knowledge about DS was associated with lower trust in DS advertisements (Karbownik et al., 2019). This discrepancy suggests that higher HL does not necessarily translate into critical skepticism toward DS use in practice, highlighting the need for further investigation.

Therefore, the purpose of this study was to investigate the association between HL and combined patterns of FV intake and DS use among Korean adults. Using nationally representative data, this study classified individuals into four distinct groups based on whether they met the FV intake recommendation and whether they used DS. By examining how HL relates to these combined dietary patterns, this study aims to provide deeper insight into the role of HL in shaping real-world nutritional strategies and to inform future nutrition education and public health interventions.

Ⅱ. Methods

Ⅲ. Results

1. Characteristics of study participants by health literacy level

Among all study participants, 25.3% had low HL, 36.9% had moderate HL, and 26.7% had high HL (data not shown). HL levels differed significantly across all covariates included in this study. Individuals who were women, aged 19-39 years, had higher educational attainment, had higher income, engaged in healthier lifestyles such as no alcohol drinking, non-smoking, and participation in more than 150 minutes/week of physical activity, had normal weight, reported better subjective health, and did not have a chronic disease were more likely to have higher HL compared with their counterparts (p<.01) <Table 1>.

<Table 1>

Characteristics of study participants by health literacy levelUnit: N (weighted %)

2. Fruit and vegetable intake and dietary supplement use by health literacy level

[Figure 1] presents FV-DS group membership, classifying participants by combined FV intake and DS use, according to HL levels. The proportion of individuals meeting FV intake recommendation did not differ significantly by HL level (28.5% for those with high HL, 31.2% for those with moderate HL, and 30.1% for those with low HL). The proportion of DS users was the highest among individuals with high HL (72.8%), followed by individuals with moderate HL (68.6%), and individuals with low HL (62.5%) (p<.001). FV–DS group membership differed significantly by HL level (p<.001). Individuals with low HL had the highest proportion in FV-only (9.4%) and None (28.1%) groups; while individuals with high HL had the lowest proportions of those in FV-only (6.3%) and None (20.9%) groups, and the highest proportion of in the DS-only (50.5%) group.

[Figure 1]

Fruit and vegetable intake and dietary supplement use by health literacy levelNotes. FV=fruits and vegetables; DS=dietary supplement; FV-only=Meeting FV intake recommendation(≥500g/day) and not using DS; DS-only=using DS and not meeting FV intake recommendation; FV&DS=Meeting FV intake recommendation and using DS; None=Not meeting FV intake recommendation and not using DS.          Proportion of FV-DS group membership by health literacy level was significantly different (p<.001).

3. Association between fruit and vegetable intake, dietary supplement, and health literacy level

As shown in <Table 2>, individuals with moderate or high HL had significantly higher odds of belonging to the FV&DS or DS-only groups rather than the None group compared with those with low HL, in both crude and adjusted models. However, HL level was not associated with the likelihood of being in the FV-only group relative to the None group.

<Table 2>

Association between fruit and vegetable intake, dietary supplement use, and health literacyUnit: Odds ratio (95% confidence interval)

Ⅳ. Discussion

This study examined the association between HL, FV intake, and DS use among Korean adults. By categorizing participants into four combined FV–DS groups, this study provided a nuanced understanding of how HL relates not only to individual health behaviors, but also to distinct dietary strategies for meeting nutritional needs. The findings demonstrated that higher HL was associated with greater DS use, whereas HL was not associated with meeting FV intake recommendations without DS use. Our findings revealed a complex relationship in which individuals with higher HL were more likely to report DS use, but not necessarily greater adherence to a food-first dietary approach.

Individuals with moderate or high HL had significantly higher odds of belonging to the FV&DS or DS-only groups compared with the None group. These findings may reflect health consciousness of people with higher HL. Previous studies reported that individuals with higher HL are more proactive about their health status and often engage in a cluster of healthy behaviors (Buja et al., 2020; Choi et al., 2025). Individuals with higher HL in this study were also more likely to engage in other health-promoting behaviors, supporting the interpretation that HL reflects a general tendency toward proactive health management. They may choose DS use as one of strategies to manage their health. Previous research in Korea also has similarly reported a positive association between the purchase of healthy whole foods and DS (Kang et al., 2017), indicating that DS use may be perceived as a component of a healthy lifestyle, rather than just a remedy for nutrient deficiency.

A noteworthy finding of this study was that individuals with high HL had a significantly higher likelihood of using DS without meeting the FV intake recommendation. Specifically, compared with individuals with low HL, they had 1.51 times higher odds of belonging to the DS-only group rather than the None group. This result suggests that higher HL does not necessarily translate into prioritizing nutrient intake from whole foods, which is a fundamental principle emphasized in dietary guidelines (World Health Organization, 2003). Although individuals with higher HL are generally expected to make more evidence-based health decisions, the present findings indicate that they may still adopt DS use as an alternative strategy for meeting perceived nutritional needs rather than increasing FV consumption. Several factors may explain this pattern. Meeting FV intake recommendations requires not only nutritional knowledge, but also economic resources to purchase fresh produce and sustained behavioral effort, including meal planning, food preparation, and healthy food choices in out-of-home food environments (Pinho et al., 2018). These requirements impose substantial time and cognitive costs, which may not be sufficiently addressed by higher levels of HL alone. In addition, high prices for fresh produce in Korea have been identified as a significant barrier to adequate FV intake (Hwang, 2024). As a result, even individuals with high HL may perceive DS use a low-effort and highly accessible strategy and favor DS over exclusive reliance on FV to meet their nutritional needs (Hoseini et al., 2021).

From a public health perspective, this finding highlights a potential mismatch between general HL and evidence-based dietary practices. The elevated odds of DS-only use among individuals with high HL suggest that general HL alone may be insufficient to promote a food-first dietary approach. It may reflect limited critical nutrition literacy, which enables individuals to critically evaluate DS marketing in light of established dietary guidelines (Velardo, 2015). While critical nutrition literacy was not directly measured in this study, our findings suggest that higher HL does not necessarily guarantee such specialized competency. In particular, higher HL may increase exposure to DS-related information through healthcare settings, digital media, and commercial marketing, without necessarily enhancing critical appraisal of their health claims. In this sense, DS-only behavior does not reflect a lack of health knowledge, but rather a pattern of health engagement in the absence of strong critical nutrition literacy. Nutrition education strategies should therefore place greater emphasis on fostering HL as well as critical nutrition literacy, enabling individuals to critically evaluate DS marketing claims and to understand the comparative benefits of whole foods versus DS. For example, public health interventions could incorporate educational programs that train individuals to critically assess DS advertisements and online nutrition information, interpret nutrition labels and health claims, and apply dietary guidelines to real-world food choices through practical learning activities such as supermarket tours or food label reading workshops.

Individuals with low HL were significantly more likely to belong to the “None” group—meeting neither the FV intake recommendation nor using DS. This pattern may reflect a general lack of engagement in nutritional health and dietary behaviors. Given that HL is a key determinant of health (Sørensen et al., 2012), this group should be prioritized as a primary target for public health interventions. Individuals in this group are likely to face multiple barriers, including limited access to health information, lower socioeconomic status, and poorer health status (Choi et al., 2025). In addition, limited HL may restrict individuals’ ability to recognize nutritional inadequacies and to seek appropriate dietary guidance, further reinforcing disengagement from healthy eating practices. Addressing these compounded barriers requires interventions that combine basic nutrition education with improved access to affordable and healthy food options. Targeted strategies are therefore needed to improve their access to, and understanding of, nutritional information and dietary requirements.

This study had several limitations that should be considered when interpreting the results. First, given its cross-sectional design, we could not establish a causal relationship between HL, FV intake, and DS use. For example, while higher HL may influence dietary strategies, it is also plausible that DS users have greater exposure to health-related information and commercial marketing, which in turn could result in higher HL scores. Second, the KNHANES data lacked information on the specific types of DS consumed and the exact dosages of nutrients obtained from them. According to the Korea Health Functional Food Association (2025), however, red ginseng and vitamins account for the largest share of the DS market. We can therefore infer that a significant portion of participants may have used DS to supplement micronutrients found in FV. Third, FV intake was estimated based on a single 24-hour dietary recall, thus it may not reflect an individual’s usual FV intake. Furthermore, DS use was defined as the consumption of supplements for more than two weeks during the past year. This discrepancy in assessment periods between FV intake and DS use poses a significant challenge to the internal validity of the group classification. Specifically, this potential mismatch may lead to misclassification bias. For example, individuals who consumed less FV on the recall day than their usual intake might have been erroneously classified into the ‘DS-only’ or ‘None’ groups. Such inconsistencies in measurement scales may lead to an over- or under- estimation of the observed associations. Finally, we used general HL rather than nutrition- or food-specific literacy. As the HLIC, HL measurement of KNHANES, does not include diet-specific items, the HL levels reported may not fully capture participants’ specific capacity related to dietary practices. However, we performed a sensitivity analysis using “nutrition label use” as a proxy for nutritional literacy and observed consistent results. Nutrition label use was associated with significantly increased odds of belonging to the FV&DS (OR: 1.65) or DS-only groups (OR: 1.71), using the None group as the reference (data not shown). This suggests that the potential bias arising from the use of a general HL measurement tool is likely limited.

Ⅴ. Conclusion

This study found that individuals with higher HL were more likely to report DS use without meeting the FV intake recommendation, suggesting that higher HL does not necessarily guarantee adherence to a food-first dietary approach. Therefore, increasing individual HL levels is not the sole solution for promoting healthy dietary behaviors such as FV consumption. To promote healthy diets, future nutrition education and communication strategies should be designed to empower individuals to effectively apply their HL competencies. Specifically, these strategies need to clarify that healthy diets are not just about the quantitative fulfillment of nutrients. Instead, emphasis must be placed on the superior, long-term health benefits of obtaining nutrients through diverse whole foods, such as FV, rather than DS. In addition, interventions aimed at strengthening critical nutrition literacy—particularly the ability to critically evaluate commercial food and DS information—are needed to support more evidence-based dietary decision-making. Alongside individual-level strategies, environmental and policy-level efforts that makes FV intake the easier choice for everyone. Comprehensive approach is required, including pricing policies to ensure affordability of FV, enhancing the accessibility of FV as snack options, and providing FV in ready-to-eat forms. These multi-faceted efforts would be beneficial to enable healthy eating for all individuals, regardless of their HL level.

Acknowledgments

This work was supported by the 2025 Research Fund of the University of Seoul.

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