Middle adulthood, generally defined as the period between 40 and 65 years of age, is a period marked by prominent physical and metabolic changes, such as loss of muscle strength, increased body fat, and heightened insulin resistance, which result from various factors, including a decline in basal metabolic rate, hormonal changes, and reduced physical activity due to aging [1]. These changes lead to the onset of major chronic diseases, and effective health management during middle adulthood becomes a critical factor that influences the quality of life in later years [2].

Among chronic diseases, diabetes is closely associated with individual lifestyle habits, such as diet and physical activity, and its onset can directly lead to a decline in quality of life [3]. In particular, individuals in their 50s and 60s, considered middle-aged, account for more than half of all patients with diabetes [4]. Previous studies based on national data have reported changes in physical activity patterns among Korean adults compared with the pre-pandemic period in 2019, particularly among older age groups [5]. These epidemiological trends suggest that diabetes is not merely a health issue in older adulthood, but a significant public health concern among middle-aged populations, highlighting the importance of early prevention and management efforts during midlife. Furthermore, inadequate prevention and management of diabetes can lead to severe complications such as cardiovascular and kidney diseases [6]. These complications not only reduce individual quality of life but also impose a substantial burden on national healthcare costs [7]. Therefore, prevention and early intervention for diabetes during middle adulthood are key determinants of health status in old age and are essential from a national public health policy perspective [2,8]. Consequently, regardless of whether diabetes has been diagnosed, both preventive and therapeutic management are necessary for middle-aged adults. Preventive management includes lifestyle modifications such as maintaining a healthy diet, engaging in regular physical activity, and monitoring metabolic risk factors, whereas therapeutic management involves the ongoing management of diagnosed conditions through medical treatment, lifestyle regulation, and adherence to recommended health behaviors. Therefore, self-care behaviors constitute a central component of health management during this life stage [9].

Orem’s [10] self-care theory emphasizes the importance of self-care, which refers to the actions that individuals must perform to maintain their health and well-being. This theory explains the need for and role of nursing based on an individual’s self-care capabilities and presents a structured framework involving the interaction among self-care demands, agency, and behaviors, thereby theoretically supporting the necessity of nursing intervention when individuals fail to meet their self-care demands [10,11].

Within this theoretical framework, diabetes represents a chronic condition characterized by high self-care demands, as it is closely associated with daily lifestyle habits such as diet and physical activity. Accordingly, the self-care behaviors required to manage diabetes may vary depending on individuals’ cognitive and functional capacities [12]. Among various self-care behaviors, aerobic physical activity plays a particularly important role, as it positively influences blood glucose regulation [13] and improves insulin sensitivity [14], thereby contributing substantially to the prevention and management of diabetes. However, despite its clinical importance, physical activity levels tend to decline with age among middle-aged adults [15]. This decline has been attributed to multiple internal and environmental barriers, including lack of motivation, limited time, insufficient social support, and existing health conditions [16]. Therefore, the simple provision of health-related knowledge alone is insufficient to promote sustained adherence to physical activity. Instead, nursing interventions that strengthen self-care agent, such as health literacy, are required to promote sustained self-care behaviors, including aerobic physical activity adherence.

Lifestyle behaviors such as regular physical activity, healthy dietary habits, and weight management play an important role in health promotion and the prevention of chronic diseases. Accordingly, growing attention has been paid to factors that facilitate the adoption and maintenance of healthy lifestyle behaviors [17]. However, studies have demonstrated that individuals’ abilities to interpret and implement health information vary depending on their level of understanding [18]. Given these differences, the ability to access, comprehend, evaluate, and utilize health-related information—known as health literacy—has emerged as a critical competency that enables individuals to effectively engage in self-care behaviors [19].

A previous study demonstrated that health literacy significantly influences disease understanding and self-care behaviors among individuals with diabetes [20]. Furthermore, low levels of health literacy were associated with difficulties in blood glucose control and an increased risk of complications [20]. Additionally, a significant correlation has been reported between health literacy and physical activity [21], suggesting that health literacy may play a role in explaining adherence to physical activity. Although previous studies have suggested that low health literacy may contribute to inadequate diabetes prevention and management [20], this study adopted a theory-driven analytical perspective grounded in Orem’s self-care framework. Based on Orem’s self-care theory, disease-related conditions are conceptualized as health deviation self-care requisites that generate new learning requirements and adaptive self-care capacities [10,12]. Accordingly, diabetes status was conceptualized not as a disease outcome variable but as a contextual condition that precedes and shapes changes in self-care agent, including health literacy [10].

Previous studies have reported that individuals with diabetes are less likely to meet recommended levels of physical activity compared with individuals without metabolic disorders [22]. Among various forms of physical activity, aerobic exercise is particularly emphasized in diabetes prevention and management guidelines because it plays a central role in improving glycemic control and metabolic health [13,14]. In addition, glycemic status may influence health literacy, as individuals diagnosed with diabetes are required to acquire disease-related knowledge and develop skills for self-management [23]. Furthermore, health literacy has been identified as an important determinant of health behaviors, including physical activity, because individuals with higher health literacy are more likely to adopt and maintain recommended lifestyle behaviors [24].Therefore, based on Orem’s self-care theory, this study aimed to examine the mediating effect of health literacy, conceptualized as a core component of self-care agent, on the relationship between self-care demands—classified by glycemic status as prediabetes, or diabetes—and the self-care behavior of aerobic physical activity adherence among middle-aged adults. By including middle-aged populations requiring both diabetes prevention and management, this study aims to provide theoretical evidence for understanding the relationships among glycemic status, health literacy, and physical activity within the framework of Orem’s self-care theory and to inform the development of nursing interventions that strengthen health literacy.

This study aimed to investigate the relationship between diabetes status and adherence to aerobic physical activity among middle-aged adults in Korea based on Orem’s self-care theory, and to verify the mediating effect of health literacy. The frequency analysis showed that 48.4% of middle-aged adults were classified as having prediabetes or diabetes, indicating that nearly half of this population falls into the at-risk group for diabetes. These findings emphasize the relevance of diabetes prevention and management during midlife and underscore the importance of improving health behaviors through the enhancement of self-care capabilities.

In this study, diabetes was not treated merely as a health outcome indicator, but was conceptualized as an indicator of self-care demands based on Orem’s self-care theory and was set as an independent variable. The association between diabetes and aerobic physical activity—a representative self-care behavior—was analyzed. Among the sociodemographic characteristics that exhibited significant differences in the chi-square analysis, sex, educational level, household income, and physical activity limitations were included as control variables. A complex sample hierarchical logistic regression analysis was performed. Model 1 confirmed that educational level and household income function as important socioeconomic contextual factors influencing adherence to aerobic physical activity, which is consistent with previous domestic and international findings [28,29]. These variables were therefore retained in subsequent models to control for background conditions affecting self-care behavior. Model 2 demonstrated that diabetes, but not prediabetes, was associated with reduced adherence to aerobic physical activity. From the perspective of chronic disease management, psychological burden, reduced self-efficacy, and disease-related physical limitations may constrain individuals’ ability to maintain regular physical activity [27]. These factors may suppress motivation and hinder the translation of self-care intentions into sustained behavioral practice. The observed differences between prediabetes and diabetes indicate that self-care behavior patterns vary according to disease stage and that diabetes substantially increases self-care demands, highlighting the need for targeted nursing interventions to support effective behavioral performance. Model 3 further demonstrated that health literacy plays a significant role in promoting adherence to aerobic physical activity, while educational level, household income, and diabetes status remained significant predictors. These findings suggest that health literacy functions as a core competency that enables individuals to interpret health-related information accurately and translate it into practical self-care behavior [30,31]. Although previous studies have suggested a potential bidirectional relationship between health literacy and diabetes-related outcomes, the present study, grounded in Orem’s self-care theory, interpreted health literacy as a cognitive capacity that is shaped and activated in response to increasing self-care demands during chronic disease management [10,12].

Orem [10] defined self-care performance as a complex and learned ability, indicating that self-care competence encompasses knowledge acquisition, cognitive judgment, and behavioral execution [32]. This suggests that self-care cannot be achieved solely through knowledge delivery, but rather requires the ability to understand and apply information in a practical context. Therefore, the findings of this study support the significance of cognitive ability as emphasized in Orem’s self-care theory. This study identified a significant difference in the adherence to aerobic physical activity between individuals with prediabetes and those with diabetes. Individuals with prediabetes may lack motivation to engage in health behaviors due to being undiagnosed or having low awareness of their condition; moreover, it has been reported that public health interventions and health education for this group are often insufficient [24]. While patients diagnosed with diabetes are more likely to receive ongoing care and education from healthcare professionals, those in the pre-diabetic stage often do not receive such support. Consequently, differences in access to information, educational opportunities, and the clarity of health messages may arise between the two groups, potentially leading to disparities in self-care behaviors [33]. Therefore, in this study, the diabetes status was conceptualized as a condition of health-deviating self-care demands, as proposed by Orem’s self-care theory. Diabetes and prediabetes were set as independent variables, and an additional mediation analysis was conducted to examine the role of health literacy in its relationship with adherence to aerobic physical activity.

Since complex sample data are constructed using stratified and clustered designs, caution is required when making estimates and interpretations compared to those based on simple random sampling. Particularly, model-based approaches such as structural equation modeling face limitations in application because they are less capable of incorporating weights and standard errors derived from complex designs [34]. Therefore, this study employed the traditional regression coefficient-based mediation analysis procedure proposed by Baron and Kenny [35], which considers a complex sampling structure to indirectly assess the significance of the mediation effect. The results indicated that prediabetes and diabetes had a negative direct effect on adherence to aerobic physical activity and that health literacy significantly increased adherence through a partial mediating effect. While logistic regression analysis indicated that prediabetes did not significantly affect adherence to aerobic physical activity, the mediation model revealed a clearer negative effect of prediabetes when the influence of the cognitive variable of health literacy was considered. This suggests that even when the same variables are used, the interpretation of results can vary depending on the analytical method employed, and that the mediation model allows for the identification of latent influences between variables through indirect pathway analysis [36]. These findings provide evidence that individuals in the pre-diabetic group, despite having lower disease awareness than those with diabetes, can still be influenced in their behavior by cognitive capacities such as health literacy. The discrepancy between the non-significant direct effect of prediabetes and the significant indirect effect observed in the mediation analysis may reflect the unique clinical and behavioral characteristics of the prediabetic stage. Prediabetes is often asymptomatic and may not be perceived as an immediate health threat, which can reduce individuals’ motivation to initiate behavioral change [24]. In this context, cognitive factors such as health literacy may function as a critical activating mechanism that facilitates risk recognition and interpretation of health information [30,37]. From the perspective of Orem’s self-care theory, prediabetes may increase self-care demands without automatically translating into behavioral action unless sufficient self-care agent is mobilized [10,12]. This finding suggests that behavioral change in the prediabetic stage is more likely to occur through cognitive and informational pathways rather than through direct disease-driven motivation.

A growing body of research suggests that health literacy plays a significant role in shaping health behaviors, a finding that is further supported by the results of this study. Given that diabetes often progresses silently or presents only mild symptoms that go unnoticed, early prevention is critical. This study conceptualized aerobic physical activity adherence as a key strategy for the prevention and management of diabetes, and demonstrated that improved health literacy can significantly enhance adherence to this approach. As reported in previous studies, individuals with higher health literacy levels tend to engage more actively in self-care behaviors such as aerobic physical activity [30], which highlights the importance of cognitive competence in translating health knowledge into practice. Therefore, it is imperative to develop nursing interventions that aim to enhance health literacy as a means of promoting preventive behaviors in diabetes care.

Orem’s self-care theory is particularly appropriate for explaining the health behaviors of individuals with chronic diseases who require ongoing self-management, as it posits that self-care demands increase in response to disease conditions. In this study, the theory served as an analytical framework, whereby diabetes status was conceptualized as an indicator of self-care demand, and health literacy was positioned as a key component of self-care agent, functioning as a mediating variable. The theoretical structure and empirical verification of the relationships among diabetes status, health literacy, and adherence to aerobic physical activity highlight the significance of this study. Moreover, by applying a mediation analysis to a large-scale, nationally representative dataset with a complex sampling design, this study provides a meaningful empirical example that may serve as a methodological reference for future research employing similar designs.

However, as aerobic physical activity represents only a part of self-care behavior and health literacy does not fully capture the entirety of self-care agent, this study constitutes a preliminary application of Orem’s self-care theory. Moreover, the reliance on self-reported questionnaires imposes limitations on the depth of measurement, which necessitates caution when generalizing the findings. In addition, although middle-aged adults were defined as individuals aged 40-64 years, heterogeneity within this age range was not examined, which may limit age-specific interpretation. Given that individuals with diabetes and prediabetes differ in self-care demands and patterns of practice, future research should stratify the analysis based on group characteristics and age subgroups and continue to link Orem’s theory with a broader range of variables beyond aerobic physical activity to provide a more comprehensive understanding.

This study applied Orem’s self-care theory to examine adherence to aerobic physical activity among Korean middle-aged adults according to diabetes status. The findings indicate that health literacy functions as a key cognitive component of self-care agent that supports behavioral change in both prediabetic and diabetic populations. In particular, the mediating role of health literacy highlights its importance as a core target for nursing interventions aimed at promoting preventive and self-management behaviors.

These results suggest that nursing strategies should prioritize health literacy enhancement to improve adherence to aerobic physical activity, especially during the prediabetic stage when behavioral change may depend more strongly on cognitive and informational pathways. Aerobic physical activity is closely associated with physiological regulation related to metabolic health, including glucose control and cardiovascular function. Therefore, improving health literacy may contribute to maintaining physiological stability and preventing the progression of chronic diseases. These findings suggest that basic nursing plays a fundamental role in assessing and monitoring physiological responses, as well as in promoting self-care behaviors through patient education and the enhancement of health literacy.

Furthermore, the application of a theory-based analytic framework using nationally representative complex sampling data provides empirical support for integrating self-care theory into population-level chronic disease prevention and management programs. Overall, this study offers practical implications for the development of theory-driven, stage-specific nursing interventions and provides a methodological reference for future research applying self-care theory to large-scale health datasets.