Associations of comprehensive oral health with body composition, physical performance, and sarcopenia among middle-aged and older adults in rural western China: Potential causal mediating mechanisms

Background Sarcopenia is a key contributor to functional decline in aging populations, yet the role of oral health in its development remains unclear. Understanding this relationship and its underlying pathways is critical for designing effective interventions to promote healthy aging. Methods We conducted the first cross-sectional study among middle-aged and older adults (aged 44–90 years) from December 2024 to January 2025 in economically disadvantaged villages of western China. A convenience sample was recruited via local health centers. Comprehensive oral health and sarcopenia risk were assessed by oral frailty index (OFI-8) and SARC-F scale, respectively. In addition, body composition, grip strength, and gait speed were standardly measured, with appendicular skeletal muscle mass index (ASMI) calculated to indicate muscle mass. Generalized linear model was conducted to examine the associations between comprehensive oral health and sarcopenia risk. Further, a general causal mediation estimated the natural indirect effects of comprehensive oral health on sarcopenia risk and the corresponding proportions mediated through muscle mass, physical performance, and dietary-intake indicators. Results Among 263 participants (mean age 64.4 ± 8.5 years; 57.8% female), 71.4% were aged ≥ 60 years. Oral frailty prevalence was high (68.4%), with 88.8% experiencing tooth loss, only 52.7% using dentures, and 6.9% visiting dentists annually. After adjusting a range of confounders, higher OFI-8 scores were statistically associated with lower ASMI, reduced grip strength, slower gait speed and an elevated risk of sarcopenia. Specifically, each 1-point increase in OFI-8 score was associated with a 30% (adjusted odds ratio 1.30, 95% CI 1.06, 1.60) higher likelihood of sarcopenia. Causal mediation analysis showed that ASMI, grip strength, gait speed, and dietary-intake indicators mediated only a modest proportion of this association: around 10% for ASMI and muscle strength, 20% for gait speed, around 5% for protein and minerals contents, and 26% for all combined. Conclusions Poor oral health was significantly associated with higher sarcopenia risk. However, conventional mediators explained only a modest proportion of this relationship, suggesting that other mechanisms, such as inflammatory or psychosocial pathways, may be involved. These findings highlight the need for integrated oral-systemic health strategies in aging populations.