Is oral frailty a cause or a consequence?

We read with interest the study by Iwasaki et al., which demonstrates that oral frailty is indirectly associated with physical frailty through the mediation of low dietary variety and social isolation.1 This study has significant implications for stratifying physical frailty among older adults with oral frailty, potentially unveiling the underlying mechanisms of its impact. However, two critical knowledge gaps remain in the literature. First, it remains unclear whether oral frailty is associated with physical frailty through the mediation of social isolation. While it is plausible that changes in dietary variety mediate the association between oral and physical frailty, it seems unlikely that oral function issues alone are responsible for social isolation from an "ecological perspective." If the impact of oral frailty were sufficiently substantial to cause dysarthria, it might indeed be linked to social isolation. However, this association is speculative, given that oral frailty in this study—defined as oral issues that are not severe enough to cause dysarthria, such as difficulties in swallowing and chewing—might not directly cause social isolation. The authors suggest that older adults with severe tooth loss often feel embarrassment and, therefore, may avoid face-to-face social interactions, such as smiling, speaking, and eating, which reduces social activities. However, this speculation is unfounded for the same reason: tooth loss is included in the authors' definition of oral frailty but is not a necessary condition. We are not dismissing the relationship between oral frailty and social isolation in research data analysis. However, the apparent mediating effect of social isolation on the relationship between oral and physical frailty, along with prior findings on the association between oral function and social activity,2, 3 likely reflects simple correlations, spurious associations, or reverse causation (see the next comment). Second, while this and previous studies4, 5 suggest that oral frailty increases the risk of physical frailty, we must reconsider whether oral frailty is always a risk factor among older adults living in the community or if it might also be a consequence or phenotype of physical frailty. Oral frailty may contribute to changes in eating habits, but it could equally be a consequence of or a co-occurring outcome alongside other conditions, including physical frailty. Current research defines individual functional decline as frailty (Fig. 1a). However, all functional components, including social and lifestyle behaviors, are interrelated rather than independent.6 Therefore, frailty should be perceived as a health condition with multiple interconnected aspects, not as individual functional impairments (Fig. 1b).7 This perspective is particularly relevant in population-based approaches to frailty screening. Oral frailty in community settings should be considered as one aspect of oral function within the broader context of frailty, synergistically rather than solely affecting health conditions. Predisposing factors for frailty include life-course determinants such as socioeconomic status, early childhood development, and lifestyle, followed by physical inactivity, chronic disease, and anorexia/malnutrition in later adulthood, forming a cycle of deterioration.7 Frailty predisposes individuals to marked declines in physical and mental function from even minor stressors, often manifesting as a "domino" effect.8 In Japan, this domino effect is proposed to often begin with social factors;9 however, there is no conclusive evidence on which factor initiates it. Therefore, a comprehensive assessment of the overall health of older adults living in community, rather than a focus on individual functional impairments, is necessary to screen for adverse outcomes (Fig. 1b).7 While we acknowledge the importance of oral function in public health and its relevance as a research topic, frailty in community-dwelling older adults should not be viewed solely through the lens of individual risk factors. Instead, frailty should be approached holistically, considering its multifaceted nature. Frailty is not just a research topic but also a clinical and public health issue within the community. Although identifying individual risk factors may be essential from a research perspective, it is crucial to promote awareness from multiple perspectives, recognizing oral frailty as both a risk factor and a consequence. None. All authors declare no competing interests. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.