Prevalence and Associations of Abnormal Levels of Vitamin B6 in People with Parkinson's Disease

BACKGROUND: In people with Parkinson's disease, abnormal levels of vitamin B6 may be associated with polyneuropathy and epileptic seizures, including medication-refractory status epilepticus. OBJECTIVES: To estimate the prevalence and explore associations of abnormal levels of vitamin B6 in people with Parkinson's disease. METHODS: In this cross-sectional study, fasting serum levels of vitamin B6 and related metabolites were measured in 144 people with Parkinson's disease randomly recruited from eligible clinic patients, compared with 144 historical controls matched for age, sex, diet, and vitamin supplementation. Mixed-effects logistic regression was used to compare the prevalences of abnormal B6 levels, and mixed-effects analysis of variance was used to compare mean B6 levels between groups. Mixed effects regression models were used to examine associations between B6 levels and pre-defined demographic and clinical variables. RESULTS: Mean age was 71 years (range = 43-87) and 38.2% were female. Almost all were treated with carbidopa/levodopa (n = 140/144, mean levodopa dosage = 800 mg/day, mean treatment duration = 78 months). The prevalence of B6 deficiency in people with Parkinson's disease was 36.1% compared to 4.9% in controls (OR = 11.4, 95% CI = 4.9-26.5, p < 0.001). The average B6 level in people with Parkinson's disease was approximately half of that in controls (ratio of geometric means = 0.49, 95% CI = 0.41-0.58, p < 0.001). The severity of levodopa-associated motor complications (p = 0.04) and the presence of epileptic seizures (p = 0.006) were associated with lower log-transformed B6 levels. CONCLUSIONS: Vitamin B6 deficiency is highly prevalent in people with Parkinson's disease. Active monitoring should be conducted in those with levodopa-associated motor complications or epileptic seizures.