Rapid population aging has positioned multimorbidity and medication burden among older adults as major global public health concerns [1, 2]. As chronic conditions accumulate with age, many older adults require multiple medications, increasing the risk of drug–drug interactions and adverse drug reactions (ADRs) [3, 4]. Polypharmacy, commonly defined as the concurrent use of five or more medications per day, has therefore been recognized as a critical indicator of vulnerability and clinical complexity in later life [5, 6]. Evidence consistently links polypharmacy to frailty, hospitalization, functional decline, and mortality [7, 8].

Medications used by older adults can influence sensory, oral, and dietary functions through diverse biological pathways. Certain drug classes, including cardiovascular agents, diuretics, and psychotropic medications, have been implicated in auditory or visual disturbances [9, 10]. Such impairments may exacerbate social isolation, communication barriers, and functional dependency, further diminishing quality of life. Despite these concerns, sensory health has rarely been examined alongside oral and dietary function in the context of polypharmacy.

Polypharmacy also directly affects the oral environment through xerogenic mechanisms. Several commonly used medications in older adults—including antihypertensives and antidepressants have been shown to induce hyposalivation and contribute to xerostomia [11, 12]. In addition, drugs with anticholinergic properties and diuretics further compromise salivary gland function, exacerbating oral dryness and mucosal discomfort [13]. As salivary flow declines, older adults are more likely to experience impaired mastication and swallowing, which negatively influences oral comfort and daily eating behaviors [12, 13]. Clinical studies have also reported that exposure to xerogenic medications increases the risk of periodontal disease and oral functional limitations, including difficulty chewing and swallowing [14]. These combined oral impairments may restrict dietary diversity and accelerate declines in nutritional and functional health.

Oral function plays an essential role in maintaining dietary intake and general health. Poor dental status, reduced masticatory performance, and inadequate denture function have been shown to limit the consumption of fruits, vegetables, and protein-rich foods [15, 16]. Furthermore, tooth loss and reduced chewing ability are associated with insufficient nutrient intake and increased risk of frailty, disability, and cognitive decline [17–19], demonstrating the central role of oral function in supporting functional independence in later life.

Dietary intake is another key health determinant that interacts with both chronic disease burden and medication use. Malnutrition and inadequate dietary intake are major threats to older adults and often coexist with multimorbidity and polypharmacy [20, 21]. Numerous medications can alter appetite, impair taste, or reduce gastrointestinal absorption, contributing to weight loss, sarcopenia, and impaired immunity [22, 23]. Given these associations, it is essential to understand how polypharmacy influences dietary patterns in older adults.

Despite the growing recognition of the risks associated with polypharmacy, few studies have assessed its combined associations with sensory, oral, and dietary functions. Moreover, it is unclear whether these associations persist after accounting for sociodemographic variables and multimorbidity, which are major determinants of medication burden in older adults. This gap limits understanding of how polypharmacy may contribute to multisystem functional decline.

Therefore, this study aimed to examine the effects of polypharmacy on three essential functional domains: sensory function, oral function, and dietary intake in a nationally representative sample of Korean older adults. By adjusting for sociodemographic characteristics and the number of chronic diseases, this study sought to clarify the independent contribution of polypharmacy to functional health outcomes and to provide foundational evidence for integrated geriatric care and oral health promotion.

This study evaluated the associations between polypharmacy (≥ 5 medications, 5.3%) and sensory, oral, and dietary functions among older adults using data from the 2023 Korean Elderly Survey (10,078 participants). Older adults with polypharmacy exhibited a higher prevalence of functional impairments compared with those without polypharmacy, including vision difficulty (60.5% vs. 40.6%), hearing difficulty (48.7% vs. 20.6%), chewing difficulty (58.9% vs. 30.1%), and difficulty eating or swallowing (20.9% vs. 6.7%) (Tables 3 and 4; all p < 0.001). These patterns are consistent with previous literature reporting greater functional vulnerability among individuals with higher medication burden [1, 2].

Sensory function showed distinct patterns after adjustment. In Model 2, vision difficulty (OR = 1.11, 95% CI = 0.91–1.36, p = 0.902), use of visual aids (OR = 0.96, p = 0.650), and use of hearing aids (OR = 1.22, p = 0.142) were no longer statistically significant, whereas hearing difficulty remained independently associated with polypharmacy (OR = 1.57, 95% CI = 1.27–1.93, p < 0.001) (Table 5). These findings suggest that sensory decline among older adults may be driven more by underlying multimorbidity than by direct pharmacologic effects of polypharmacy, aligning with earlier evidence on medication-related auditory and visual disturbances [9, 10].

In contrast, oral function remained significantly associated with polypharmacy even after adjusting for chronic diseases. Chewing difficulty (OR = 1.39, p = 0.002), denture use (OR = 1.67, p < 0.001), swallowing difficulty (OR = 1.48, p = 0.002), and unmet dental care needs (OR = 1.51, p = 0.021) all remained significant in Model 2 (Table 6). These findings are consistent with previous evidence showing that xerogenic medications such as antihypertensives, antidepressants, anticholinergics, and diuretics contribute to hyposalivation [12–15], which can translate into measurable declines in oral function. Reduced salivary flow interferes with bolus formation, lubrication, and swallowing efficiency [24], and similar mechanisms were reflected in the present study.

Dietary function showed significant differences in the crude analysis, including higher rates of non-consumption of fruits, non-consumption of vegetables, and eating fewer than two meals per day among adults with polypharmacy. However, these associations were no longer statistically significant after adjusting for chronic disease burden in Model 2, suggesting that the relationship between polypharmacy and dietary behaviors may be indirectly mediated through oral functional decline and multimorbidity rather than representing a direct pharmacologic effect. Reduced masticatory capacity often leads older adults to avoid fibrous and protein-rich foods, resulting in inadequate nutrient intake, a pattern consistent with previous evidence linking oral frailty with nutritional and functional decline [25, 26]. Dietary diversity has also been identified as an important determinant of cognitive and overall health status in older adults [27]. Furthermore, certain medications commonly prescribed in this population have been shown to influence appetite regulation and physiological functioning, thereby negatively affecting dietary behaviors [28].

The concurrent decline in sensory and oral function identified in this study also aligns with emerging concepts of oral frailty and frailty trajectories among older adults [29, 30]. Oral function decline is considered an early marker of systemic frailty, and the observed association between hearing impairment and declines in cognitive and physical functioning is consistent with previous evidence [31, 32]. These findings indicate that multisystem functional vulnerabilities tend to co-occur among older adults with polypharmacy, underscoring the need for clinical intervention.

Furthermore, polypharmacy has been described not merely as a numerical count of medications but as an indicator of underlying systemic vulnerability and multimorbidity [33, 34]. In the present study, oral functional impairments remained independently associated with polypharmacy even after adjustment for chronic disease burden, reinforcing the clinical relevance of this relationship. These findings emphasize the importance of comprehensive geriatric strategies that integrate deprescribing, xerostomia management, improved access to dental care, and nutritional counseling [35, 36]. Such approaches may help disrupt the cycle between polypharmacy and functional decline and promote healthy aging.

This study has several limitations. First, the cross-sectional design precludes causal inference regarding whether polypharmacy directly contributes to functional decline. Second, all sensory, oral, and dietary measures were based on self-report, which may introduce recall or social desirability bias. Third, detailed information on medication classes, dosages, and pharmacologic interaction burden, including cumulative anticholinergic load, was not available, which limits mechanistic interpretation. Future research that incorporates longitudinal designs and medication-specific analyses is warranted.

This study demonstrates that polypharmacy is closely linked to functional vulnerability in older adults, with oral function showing persistent independent associations even after adjusting for multimorbidity. These results highlight the need for integrated geriatric care that combines medication review, oral function management, and nutritional support to mitigate the adverse functional impacts of polypharmacy and promote healthy aging.