 Based on Parkinsons disease PDvitamin 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. 