Globally, the population is aging rapidly [1]. In 2023, the elderly population in South Korea accounted for 18.4% of the total population, showing a rapid pace of aging [2]. In 2022, the number of elderly individuals aged 65 and over covered by health insurance was 8.75 million, with medical expenses for the elderly totaling 45.7 trillion 647 billion won, which is a 1.4-fold increase compared to 2018, indicating an increasing social and national burden [3]. Therefore, preparation for preventing and managing health issues from middle age onwards is necessary for a stable retirement. However, due to experiencing declines in physical, mental, and biological capacities and health, improper management of middle age can lead to significant challenges in old age [4]. Therefore, preventive care is crucial for preparing for life in old age, and various strategies need to be developed to enhance the quality of life (QoL) in middle age.

Aging is a universal process that all humans undergo throughout their growth and development. When aging leads to visual impairment, hearing impairment, or cognitive decline, it can significantly influence QoL [5-7]. Vision, being one of the most critical sensory functions of the human body, when impaired, can negatively affect an individual's daily life and may lead to functional disabilities and other health issues [8]. Visual impairment affects work performance, mobility, and contributes to depression and anxiety, with more severe visual impairment leading to a greater reduction in QoL [5,9]. Presbyopia, which occurs due to a decrease in the ability to adjust focus, often first manifests in the early 40s, leading to the alternative term 'middle-aged vision [10].' These symptoms of presbyopia during middle age can significantly impede daily activities, occasionally diminishing work productivity and overall life contentment. In the United States, the prevalence of visual impairment is 17% among adults aged 45 and older, rising to 26.5% among those aged 75 and older [11]. Aging is a prominent risk factor for visual impairment, with a higher incidence among the elderly compared to middle-aged adults. Despite this, the influence of visual impairment on QoL among middle-aged adults should not be underestimated, underscoring the need for targeted management and intervention.

People experiencing hearing impairment negative influences in both physical and mental domains. According to a study utilizing census data from the UK, it was reported that one out of every ten middle-aged individuals suffers from significant hearing impairment, with the prevalence increasing particularly with advancing age, especially after the mid-50s [12]. Hearing impairment is associated with an increased risk of dementia [13], depression, higher levels of stress, somatization, loneliness, and a negative influence on QoL [6,14,15]. This is increasingly considered a significant public health issue, highlighting the growing need for hearing care management among the middle-aged population.

People with low mastication ability are associated with dementia and Alzheimer's disease [16], which leads to a lower QoL and decreased survival rates [17,18]. Based on a study investigating masticatory discomfort according to types of dental prostheses using the Korea National Health and Nutrition Examination Survey (KNHANES), the incidence of discomfort stood at 14.2% among those in their 40s, showing a marked rise among individuals in their 50s. Additionally, the proportion of those experiencing masticatory discomfort increased with age [19]. Masticatory ability influences the enjoyment of meals and diet, and it is also linked to QoL. Hence, it is crucial to explore the connection between the QoL in middle age and issues such as visual and hearing impairments, as well as masticatory discomfort.

Coexistence of sensory impairments negatively influences depression, loneliness, social isolation, self-esteem, and autonomy, leading to reduced quality in physical, mental, and social functions [20,21]. Dual sensory impairment of visual and hearing in middle-aged individuals increased ninefold among those in the oldest age group, 65-69 years, compared to those in the 40-44 years age group. Additionally, visual and hearing impairments often occur concurrently, and when both sensory issues are present, the age-related proportional increase is greater than when either visual or hearing impairment is experienced independently [22].

Dental health can also affect hearing. Sound stimuli through the teeth and jaw are transmitted to the cochlea via bone conduction, a phenomenon known as "dentauralhearing [23]." When a sound source is applied to the skull, vibrations can pass through it due to the skull's fibrous-elastic properties. It is unclear how this mechanical energy affects the ear sac, middle ear structures, and external auditory canal [24]. People who have lost more than half of their teeth are 1.64 times more likely to experience hearing impairment compared to those who have not [25]. Additionally, in a study evaluating hearing after providing implant-supported complete dentures to completely edentulous individuals, it was reported that implants improved bone conduction similar to teeth, enhancing hearing 1 month after implant placement [26]. Furthermore, individuals without occlusal vertical dimension, which is the vertical distance when the teeth of the maxilla and mandible come into contact, showed higher rates of hearing impairment compared to those with occlusal vertical dimension [27]. Based on these studies confirming the association between dental and hearing health, it is necessary to consider sensory impairments and masticatory function together.

Individuals with masticatory issues and comorbidities are more likely to require dental treatment compared to those without these conditions [28]. When multiple tooth loss and masticatory dysfunction occur, the likelihood of cognitive impairment is significantly higher [15]. If malocclusion and temporomandibular joint disorders accompany these issues, masticatory dysfunction becomes more pronounced, negatively influencing oral health-related QoL [29]. Such sensory and masticatory function impairments have long-term effects on the QoL, leading to a deterioration in physical, emotional, and social functioning over the years [21]. With the aging demographic trend persisting, age-related diseases will become a growing concern not only domestically but also globally for decades to come.

However, research on sensory and functional impairments has mainly focused on individuals aged 65 and above due to rapid aging, with limited and insufficient studies targeting the middle-aged population in the transitional period to old age. While several previous studies have explored the influence of dual sensory impairment, encompassing both visual and hearing impairments, on QoL, it was challenging to find research specifically examining the effects of three or more coexisting issues such as masticatory discomfort on QoL.

This study aims to understand the influence of coexisting visual impairment, hearing impairment, and masticatory discomfort on the QoL during middle age, with the goal of highlighting the importance of health management and providing foundational data for developing effective nursing practices to facilitate a healthy transition from middle age to old age.

This study sought to explore the imfluence of the coexistence of visual impairment, hearing impairment, and masticatory discomfort on the QoL among adults aged 40 to 64 using the raw data from the 8th KNHANES conducted in 2019 and 2020.

In this study, a diminished QoL was observed among women, those with lower educational levels, non-drinkers, and non-obesity individuals, as well as those with diabetes. A study investigating factors influencing QoL among middle-aged individuals also found that general characteristics and health-related behaviors such as sex, educational level, drinking frequency, and obesity status significantly affected QoL [32]. Among characteristics related to chronic conditions, although measurement tools varied across study targeting adults, those with diabetes complications consistently exhibited lower QoL [34]. Furthermore, a study investigating the prevalence of chronic diseases among adults under 64 according to their QoL found a significantly higher prevalence of diabetes among those with lower QoL [33], which aligns with the results of this study. A study measuring QoL among adults found that as age increases from the 30s to the 40s and beyond, QoL tends to decline [35]. Therefore, it is important to manage the QoL during middle age to prepare for old age, emphasizing the need for strategies to address health-risk behaviors and disease prevention during middle age.

The results of this study indicate that visual impairment, hearing impairment, and masticatory discomfort each had a significant influence on QoL when present individually. A previous study, utilizing the KNHANES to measure vision among adults aged 19 and above, found that visual impairment and ocular diseases had an influence on activity limitation and QoL [36]. In a previous study focusing on middle-aged individuals using self-report measures, hearing impairment was found to significantly impair QoL [12]. Additionally, a study on the association between oral health status and QoL among adults under 64 found that masticatory discomfort had an influence on QoL [37], aligning with the findings of our study.

However, in this study, among participants with coexisting visual and hearing impairments and masticatory discomfort, those with only visual impairment, only hearing impairment, or only masticatory discomfort (Category A) did not show a significant influence on QoL. This difference is likely due to variances in the analysis methods between previous studies and our study. In previous studies, respondents with single occurrences of each independent variable might have been mixed with those who responded to other variables as well. However, in our study, individuals with only one of the three main independent variables—visual impairment only, hearing impairment only, or masticatory discomfort only—did not include respondents who answered to other variables. Furthermore, since our study focused on middle-aged individuals and had a limited number of participants in the categories of visual impairment only, hearing impairment only, and masticatory discomfort only among the coexistence states, this might have contributed to the findings. Therefore, it is suggested that future research, using not only the raw data from the 2019 and 2020 KNHANES but also a larger sample, is needed. Furthermore, the measurement tools for variables in our study were self-report measures, whereas previous studies utilized objective measurement tools, leading to methodological differences. Therefore, future research utilizing the same measurement tools is necessary for comparability.

Among the coexistence of two variables from visual impairment, hearing impairment, and masticatory discomfort (Category B), only visual impairment and hearing impairment, as well as visual impairment and masticatory discomfort, had a significant influence on QoL. This is consistent with previous studies showing that when visual and hearing impairments coexist, the QoL is lower than when each condition occurs alone [23]. Both visual and hearing impairments strongly affect subsequent functions such as physical function, mental health, and social function. However, visual impairment has a broader influence on functional status compared to hearing impairment [38]. Thus, while managing hearing impairment and masticatory discomfort is important, the management of visual impairment is of even greater significance due to its more extensive influence on daily life. The coexistence of both hearing impairment and masticatory discomfort did not exert a significant influence on QoL. Previous studies have reported an association between dental conditions and hearing [25-27,39], but research on the coexistence of masticatory function and hearing impairment is rare. Further investigations are required to examine the influence of the coexistence of hearing and masticatory function on QoL.

Finally, when all three conditions of visual impairment, hearing impairment, and masticatory discomfort coexisted (Category C), the QoL was significantly lower compared to individuals without all three conditions. Since vision allows people to detect clues about their environment and plan physical movements, a decline in visual acuity can lead to reduced ability to detect environmental hazards, potentially resulting in a decrease in physical functionality [40,41]. Similarly, hearing impairment increases the effort required to understand speech, altering neural activity in key auditory processing areas, which affects cognitive functions and may lead to impairments in memory and activities of daily living [42]. Issues with the primary function of teeth—mastication—can lead to decreased secretion of digestive enzymes, resulting in digestive problems. It can impair an individual's ability to eat, speak, socialize, and perform various everyday activities [7,43]. It is known from previous studies that while the visual and hearing impairments, as well as masticatory discomfort [20-22,29], each have a negative influence on an individual's QoL, the QoL is even lower when two or more of these issues coexist. Research on the influence on QoL when three factors—visual and hearing impairments, and masticatory discomfort—coexist is scarce. However, the results of this study confirm that when these issues are present together, they affect basic living activities, leading to a decline in QoL. If these impairments coexist in middle age, it can be assumed that they may persist into old age, with a cumulative influence on reducing QoL. The significance of this study lies in its confirmation that the coexistence of age-related sensory and functional impairments has a significantly greater influence on QoL than when they exist in isolation. This highlights the need to promote awareness of preventive healthcare for middle-aged individuals, as they are at a critical stage preceding old age. As aging progresses, visual and hearing impairments, and masticatory discomfort are often viewed as natural occurrences, leading to a lack of attention to potential comorbidities when interacting with patients in clinical nursing practice. In clinical nursing practice, it's essential to consider whether visual impairment, hearing impairment, and masticatory discomfort are co-occurring, rather than addressing them individually when assessing patients. This approach is crucial because when assessing patients, those with coexisting visual impairment, hearing impairment, and masticatory discomfort typically have lower QoL compared to those without such co-occurrences. This necessitates more attentive nursing care. By educating junior practitioners about this approach and implementing it in clinical nursing practice, the quality of nursing care can be improved, which is expected to lead to more effective health management for patients. In the midst of the human life cycle, it's crucial for those in middle age, transitioning between life stages and nearing old age, to prevent the coexistence of health conditions and prioritize consistent healthcare management. The prevalence of visual impairment, hearing impairment, and masticatory discomfort increases with age, influencing QoL. Middle-aged individuals experiencing sensory and functional impairments will continue to face quality-of-life challenges as they age. Given this, it's crucial to focus on health management at both personal and national levels to address these ongoing influences. On a personal level, maintaining healthy habits and regular physical activity are essential. On a national level, it's important to focus efforts on education, promotion, and support for early detection and prevention of coexisting health issues through initiatives such as health screenings.

This study aimed to investigate the influence of coexistence of visual impairment, hearing impairment, and masticatory discomfort on QoL. Nevertheless, there are certain constraints to take into account. Firstly, the sample size was limited as the study only focused on middle-aged individuals using raw data from 2019 and 2020, which may restrict the generalizability of the findings. Secondly, the measurement methods for visual impairment, hearing impairment, and masticatory discomfort tools involve a mixture of disease diagnosis and self-reporting, potentially reducing objectivity.

This study examined how the coexistence of visual impairment, hearing impairment, and masticatory discomfort influences the QoL in middle-aged individuals, using raw data from the 8th KNHANES 2019, 2020. When these conditions existed singly, they did not significantly affect the QoL compared to individuals without any of the three conditions. However, when two conditions coexisted, only visual impairment with hearing impairment, and visual impairment with masticatory discomfort had an effect on QoL. Individuals with all three conditions experienced a significantly lower QoL.

The significance of this study lies in demonstrating that when visual impairment, hearing impairment, and masticatory discomfort—commonly seen as natural processes of aging—coexist, they influence the QoL in middle-aged individuals. Therefore, proper health management during middle age is crucial for a healthy transition into old age, necessitating both personal and national support to enhance the QoL.

Drawing from the conclusions of this study, the following suggestions are put forward. Conduct more research on how combined sensory and masticatory function impairments influence QoL, focusing on middle-aged individuals with a larger sample size. Use objective assessment tools to evaluate key variables for improved accuracy in future studies. Investigate how hearing impairment and masticatory discomfort affect QoL.