Vitamin B12, also known as cobalamin, has a central role in how the entire nervous system functions; something which is especially important for cognitive abilities. Vitamin B12 is involved in the synthesis of DNA and red blood cells, as well as the synthesis of fatty acids. Vitamin B12 blood levels below 200pg/ml indicates a deficiency. A healthy diet gives the body sufficient amounts of vitamin B12. The lack of vitamin B12 is common in vegetarians, vegans, older people and people who are genetically prone to the lack of vitamin B12.