In a recent study of early Parkinson disease (PD), low B12 status was common and, at baseline, predicted greater worsening of mobility among patients. In addition, elevated homocysteine predicted greater cognitive decline in patients with early PD. Researchers measured vitamin B12 and other B12 status determinants (methylmalonic acid, homocysteine, and holotranscobalamin) in 680 baseline and 456 follow-up serum samples collected from DATATOP participants with early, untreated PD. Borderline low B12 status was defined as serum B12 <184 pmol/L (250 pg/mL), and elevated homocysteine was defined as >15 µmol/L. Outcomes included the Unified Parkinson Disease Rating Scale (UPDRS), ambulatory capacity score, and Mini Mental State Examination (MMSE), calculated as annualized rates of change. They found:

• At baseline, 13% had borderline low B12 levels, 7% had elevated homocysteine, whereas 2% had both.
• Elevated homocysteine at baseline was associated with worse scores on the baseline MMSE.
• Analysis of study outcomes showed that, compared with the other tertiles, participants in the low B12 tertile (<234 pmol/L; 317 pg/mL) developed greater morbidity as assessed by greater annualized worsening of the ambulatory capacity score.