The Red Blood Cell Distribution Width-to-Albumin Ratio’s Role in Parkinson’s Disease: A Cross-Sectional Study

Background: The red blood cell distribution width-to-albumin ratio (RAR) serves as an indicator of systemic inflammation and nutritional status. The precise relationship between the RAR and Parkinson’s disease (PD) prevalence remains unclear. Methods: This study examines the association between the RAR and PD in U.S. adults aged over 40, utilizing data from the NHANES (2003–2018). Logistic regression, subgroup analyses, and restricted cubic spline (RCS) models were utilized to evaluate the relationship between the RAR and PD prevalence. Results: Of 22,617 participants, 287 had PD. The mean RAR was higher in PD (3.32 ± 0.04) vs. that in non-PD (3.16 ± 0.01; p < 0.0001). Each unit increase in the RAR was linked to a 47% rise in the PD odds (OR = 1.47; 95% CI, 1.16–1.86; p < 0.05). The prevalence of PD in the highest quintile (Q3) was 1.921 times higher than that in the lowest quintile (Q1) (OR = 1.921; 95% CI, 1.128–3.270). Higher RAR values were significantly associated with increased odds of PD prevalence (p-values for trend < 0.05). The RCS analysis indicated a nonlinear association between the RAR and PD prevalence odds (p = 0.0423), with RARs ≥ 3.12 associated with increased odds of PD prevalence. Subgroup analyses and interaction tests validated the robustness of the findings regarding the association. Conclusions: This study found a positive nonlinear relationship between the RAR and PD prevalence. The odds of PD prevalence increased notably when the RAR exceeded approximately 3.12, and they continued to rise with increasing RARs. Due to the cross-sectional design, causality cannot be confirmed. Further research is needed to explore the mechanisms linking the RAR and PD.