Dementia is not a specific disease but is rather a general term for the impaired ability to remember, think, or make decisions. Alzheimer’s disease (AD) is a devastating progressive neurodegenerative disease and the most common form of dementia for which no effective cure was found until today. Alzheimer’s disease is characterized by memory loss, impaired spatial and temporal orientation, agnosia, language disturbance, mood disturbance, wandering, and other cognitive and neuropsychiatric functions that reduce the ability to carry out the activities of daily living. B vitamins, including vitamin B12 (cobalamin), are essential water-soluble micronutrients that have to be taken up in sufficient quantities from one’s diet. They are crucial for maintaining neuronal health and hematopoiesis. Vitamin B12 is believed to be an antioxidant vitamin by different mechanisms, including direct scavenging of reactive oxygen species (ROS), particularly superoxide in the cytosol and mitochondria, and indirectly stimulating ROS scavenging by preservation of glutathione. Vitamin B12 supplementation exerts positive effects in respect to AD pathology not only in transgenic AD model mice but also in wildtype animals. Vitamin B12 supplementation in hyperhomocysteinemic rats could antagonize homocysteine-induced changes in APP processing and tau phosphorylation. Vitamin B12 protected scopolamine-injected rats and inhibited hippocampal inflammation and apoptosis and preserved pre- and post-synaptic proteins and possibly synaptic integrity in hippocampus by increasing synaptic plasticity