There is a known association in the research literature. Data suggest people with Parkinson's may have lower vitamin B12 levels, see this meta-analysis, and that B12 levels may decrease at Parkinson's progresses.
There is also some evidence that lower B12 levels may be linked to greater memory and thinking issues. Studies have also investigated the link between B12 intake and Parkinson's risk, but there seems to be no association here.
The studies suggest that taking B12 supplements may benefit some individuals with Parkinson's, but there is a lack of research evidence about how much or how often this should be prescribed. I hope this information is of use, but for advice we would recommend speaking to your specialist, Parkinson's nurse or GP.
With best wishes,
The Parkinson's UK Research Team