Vitamin B12 is an essential water-soluble vitamin that is commonly found in a variety of foods such as fish, shellfish, meat, and dairy products. Vitamin B12 is frequently used in combination with other B vitamins in a vitamin B complex formulation. It helps maintain healthy nerve cells and red blood cells, cofactor for enzymatic reactions; it also helps in the metabolism of odd chain fatty acids, and methylation of homocysteine. DEFICIENCY of vitamin B12 (found in almost 30% of people above 60 years) results from inadequate absorption; vegans who do not take vitamin supplements, patients with gastrointestinal disease and in chronic alcoholics. It can lead to abnormal neurologic and psychiatric symptoms. These symptoms may include: ataxia (shaky movements and unsteady gait), muscle weakness, spasticity, incontinence, hypotension (low blood pressure), vision problems, dementia, psychoses, and mood disturbances. Vitamin B12 deficiency is also associated with megaloblastic anemia, damage to the white matter of the spinal cord and brain, and peripheral neuropathy. HIGH levels of vitamin B12 are associated with hematological disorders and liver disease, and occasionally in subjects with no other pathology (idiopathic hypervitaminosis).