Vitamin B12 (or Methylcobalamin), you could say, has the most publicity out of all the B vitamins. It is common opinion that it is the most important and has the most use in the human body but continuous research will keep changing that opinion. It is, if nothing else, the most chemically complex out of all the vitamins.

Uses of B12
Vitamin B12 is the general name for a group of biological compounds called cobalamins. These are like haemoglobin except that they carry cobalt in the blood instead of iron. An important use of vitamin B12 is its use for the growth and protection of the nervous system. A study in 1994 found that vitamin B12 actually had the ability to repair nerve damage. All the B vitamins aid in the maintenance of the skin, eyes, liver and mouth as well as aiding in maintaining normal brain function and healthy muscle tone in the gastrointestinal tract. It is essential in the process in which protein is built and then synthesised for use by the cardiovascular system. It is also important for the prevention of anaemia as is aids folic acid in the regulation of red blood cells

Sources
Vitamin B6 is found in all foods, however the best sources of Vitamin B12 is found in meats, eggs, herring, kidney, liver, milk and dairy products and a variety of seafood. It is also found in many vegetables and many nutritionists argue that this is the best source to obtain a dietary form of vitamin B12 (along with numerous other nutrients). However to obtain the correct amount, a normal vegetarian would have to take a vitamin B12 supplement as they would not be able to consume enough in their diet. Most of the vitamin B12 in the body is synthesised by bacteria present in the large intestine.