Parkinson’s Disease and Frailty: A Two-Way Link Across Aging

<b>Background:</b> Parkinson's disease (PD) and frailty frequently co-occur and may interact bidirectionally through shared mechanisms of aging biology, mitochondrial dysfunction, inflammation, and reduced physiological reserve. <b>Objective:</b> We aimed to synthesize current evidence on prevalence, directionality, clinical overlap, adverse outcomes, and management implications of the PD-frailty nexus. <b>Methods:</b> A narrative review of epidemiologic, cohort, and interventional studies was performed, examining frailty in PD and PD risk in prefrail/frail populations, plus trials of multimodal interventions. <b>Results:</b> Frailty is common in PD, affecting approximately one-third of patients overall and becoming more prevalent as the disease advances. It independently predicts falls, cognitive decline, hospitalization, institutionalization, and mortality. Large cohorts suggest prefrailty/frailty is associated with incident PD risk, supporting a potential bidirectional association rather than direct causation. Diagnostic complexity arises because PD motor and non-motor features overlap with frailty constructs, risking misclassification. Management based on Comprehensive Geriatric Assessment (CGA) enhances personalized, multidisciplinary care. Exercise, particularly combined aerobic and resistance training reduces frailty and improves mobility, postural control, and quality of life. Complementary nutritional strategies, including muscle-targeted supplementation, can further strengthen rehabilitation outcomes, while careful attention to social determinants and polypharmacy remains essential to optimizing overall health and functional independence. <b>Conclusions:</b> Frailty is best understood as a clinical marker of vulnerability within PD and a correlate of more adverse trajectories rather than a proven causal determinant. Systematic frailty assessment integrated into PD care may help refine prognosis, individualize treatment, and support efforts to preserve independence. Priorities include PD-adapted frailty tools, CGA implementation, and rigorous trials of combined exercise-nutrition programs.