Vitamin B12 Status and Response to Vitamin B12 Supplementation in Patients With Parkinson's Disease

Based on Parkinson's disease (PD)/vitamin B12 deficiency symptom overlap and PD patients' propensity to avoid protein (the dietary source of vitamin B12), this study proposes to prospectively investigate the vitamin B12 status of PD patients over time. In addition, this study will provide critical pilot data evaluating the efficacy of treating those patients considered to have below-normal vitamin B12 levels in serum. Further, it will also explore the concept that supplementing PD patients having "low-normal" vitamin B12 levels with vitamin B12 improves either the non-motor PD symptoms or homocysteine levels in PD patients receiving levodopa. Study Hypotheses: 1. Serum cobalamin (B12) concentrations in patients with Parkinson's disease (PD) are significantly lower than B12 concentrations in a) cohabiting spousal caregiver controls; and b) population-based, age-matched controls. 2. Supplementation with B12 in levodopa-treated PD patients with low (\<200 pg/ml) or low-normal (200-300 pg/ml) serum B12 levels is associated with significant improvement in their non-motor symptoms and reduces total plasma homocysteine concentration \[Hcy\], a known biomarker for risk of dementia and cerebrovascular disease.