Association of serum homocysteine, folate, and vitamin B₁₂ levels with cognitive function in levodopa-naïve patients with Parkinson’s disease and mild cognitive impairment

INTRODUCTION: The aim of this study was to examine changes in serum concentrations of total homocysteine (tHcy), folate, and vitamin B₁₂ (vit B₁₂) in levodopa-naïve patients with Parkinson's disease and mild cognitive impairment (PD-MCI) and to evaluate their association with cognitive function. MATERIAL AND METHODS: A retrospective analysis was conducted in 192 levodopa-naïve patients with early idiopathic Parkinson's disease (PD). On the basis of Montreal Cognitive Assessment (MoCA) scores, participants were classified into a PD-MCI group (n = 89) and a Parkinson's disease with normal cognitive function (PD-NCI) group (n = 103). In addition, 89 healthy individuals who underwent physical examination during the same period were included as a control group. Serum levels of tHcy, folate, and vit B₁₂, as well as cognitive function scores, were compared among the three groups. RESULTS: Compared with the PD-NCI group, patients in the PD-MCI group demonstrated significantly lower scores in visuospatial and executive function, attention and calculation, abstraction, and delayed recall (p < 0.05). Serum tHcy levels were significantly higher in the PD-MCI group than in both the PD-NCI and control groups, whereas folate and vit B₁₂ levels were significantly reduced (p < 0.01). Among patients with PD, MoCA scores in the high tHcy subgroup were lower than those in the normal tHcy subgroup. Partial correlation analysis demonstrated that MoCA scores were negatively correlated with tHcy levels and positively correlated with folate and vit B₁₂ levels in patients with PD-MCI. CONCLUSIONS: These findings suggest an association between elevated serum tHcy, reduced folate/vit B₁₂ levels, and cognitive impairment in PD-MCI. Folate and vit B₁₂ supplementation warrants further investigation in longitudinal or interventional studies.