Vitamins in Alzheimer's and Parkinson's Disease

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the most common neurodegenerative disorders, with slow cognitive and motor decline, high societal costs, and a dearth of disease-modifying therapies. There is an increasing body of research that supports the role of nutritional neuroscience, especially as it relates to vitamin biology, in establishing a pathological state for these diseases. Vitamins are most often used as important cofactors in metabolic pathways, but research suggests they have more extensive neuroprotective mechanisms for the regulation of oxidative stress, mitochondrial function, neurotransmission, neuroinflammation, and epigenetic mechanisms. This chapter will detail mechanistic and therapeutic perspectives of the roles of vitamins in AD and PD. Vitamin A and its derivatives affect neurodevelopment and amyloid–tau pathology; B-complex vitamins affect homocysteine metabolism, DNA methylation, and neuronal energy status; vitamin C can act as a strong antioxidant and cofactor for dopamine biosynthesis; vitamin D is involved in calcium signaling and immune function; and vitamin E protects neuronal membranes from lipid peroxidation and amyloid toxicity. Newer information on the role of vitamin K, niacin, and biotin also illustrates their roles in synaptic function, NAD⁺ metabolism, and neuronal cytoprotection. Preclinical and clinical evidence suggests that vitamins may provide therapeutic benefit, although conflicting results arise from heterogeneity of study design, dose, bioavailability, and stage of disease. The chapter stressed the additive effects of combined vitamin supplementation; interactions with minerals and phytochemicals; and integration with pharmacological therapies. This chapter also highlighted the translational challenges associated with vitamins, including the need for biomarker-based precision nutrition, delivery systems using nanocarriers, and large-scale randomized controlled trials. This chapter suggests that vitamins have promise as add-on therapies to pharmacological treatments in the context of a clinical perspective, while considering all of the mechanistic data reviewed. While we cannot consider them as effective monotherapy, vitamin-based strategies for AD and PD may provide a multi-targeted approach that slows neurodegeneration. Additionally, used in conjunction with lifestyle modification and pharmacological therapies, vitamin-based strategies could promote resilient brains for patients.