Twenty-five PD patients were studied, with 15 (60%) developing dementia. Patients not developing dementia had higher baseline levels of vitamin B12 at PD diagnosis (648.5 ng/L vs 452 ng/L, p=0.02). Higher dementia risk trended toward significance (RR 4.8, 95% CI 0.96-23.8) in the 1^st tertile and was significantly higher in the 2^nd tertile (RR 5.5, 95% CI 1.1-27.9) compared with the 3^rd tertile. Vitamin B12 cutoff of 587 ng/L was the most sensitive (87%) and  specific (70%, AUC 0.79) distinguishing patients without dementia. PD patients with vitamin B12 levels <587ng/L were 5.4 times more likely to develop dementia, with 50% having dementia within 5 years of PD diagnosis compared with 11% in those with a vitamin B12 level of >587ng/L (p=0.03).

Higher levels of vitamin B12 at PD diagnosis are associated with reduced risk of dementia. This relationship is complex and potentially related to cholinergic neurotransmission and alpha-synuclein accumulation. Vitamin B12 supplementation as a symptomatic and potentially disease modifying therapy in Parkinson’s disease deserves further study.