Oral microbiome and Frailty: Insights from NHANES 2009-2012 and Mendelian Randomization Analysis

Background Frailty is associated with increased risks of disability, hospitalization, and mortality. Emerging evidence suggests that the oral microbiome may influence frailty development, but population-based evidence is limited and causal relationships remain unclear. This study explored the link between oral bacteria and frailty, using genetic analysis to investigate causality. Methods We analyzed data from 2,696 adults aged ≥50 years in NHANES 2009-2012. Oral microbiome diversity was assessed using 16S rRNA gene sequencing. Frailty was measured using a 36-item Frailty Index. Survey-weighted linear regression and restricted cubic spline models examined associations between four α-diversity indices and frailty. β-diversity was quantified using Bray-Curtis dissimilarities and compared by frailty status using PERMANOVA. Bidirectional two-sample Mendelian randomization (MR) using GWAS data assessed causal relationships between taxa and frailty. Results Lower α-diversity across all four indices were associated with higher frailty scores (P < 0.050). β-diversity differed by frailty (P = 0.001). MR analyses indicated that in saliva, Campylobacter_A, Saccharimonadaceae, and TM7x were protective, whereas Gemella was associated with increased frailty risk. In tongue samples, Saccharimonadaceae was a risk factor, while Fusobacterium, TM7x, and Solobacterium showed protective effects. Conclusions Oral microbiome diversity is inversely associated with frailty in U.S. adults, and MR analyses identify specific oral taxa potentially involved in frailty development. These findings provide population-level evidence and genetic support for the oral microbiome as a potential modifiable target to promote healthy aging.