Vitamin B12 exists in several forms and has the most complex chemical structure of all the vitamins. This is because it binds to cobalt, forming a cobalamin compound. B12 is a water soluble vitamin, meaning some of the leftover amount is flushed away in the urine. Most water soluble vitamins cannot be stored by the body, but B12 compounds can be stored in the liver. The body uses vitamin B12 in the form of 5-deoxyadenosylcobalamin and methylcobalamin. Vitamin B12 is found in some foods and is available by prescription or as a dietary supplement.
Normal B12 Levels and RDA
The normal blood level of vitamin B12, measured in picograms per deciliter, is 200 to 900 pg/dL. Any level below 200 pg/dL indicates a deficiency of B12. Vitamin B12 is measured using a fasting blood test, so you will not be able to eat or drink anything for six to eight hours prior to having your blood drawn. Some drug and herbal supplements, including colchicine and phenytoin can affect the results, so be sure to advise your physician of everything you are taking.
The Office of Dietary Supplements lists the RDA, or Recommended Dietary Allowance, of vitamin B12 for adults as 2.4 to 2.8 mcg. This is the amount of vitamin B12 that you need to ingest daily in order to keep your levels in the normal range.
Food Sources of Vitamin B12
Vitamin B12 is synthesized by bacteria present in a variety of animal products. It needs to bind to protein so it is not found in many plant products. Liver, clams and mussels contain the highest amounts of vitamin B12. Other foods that contain vitamin B12 include rainbow trout, crab, salmon, beef, haddock, chicken, eggs and milk. Some processed foods, such as breakfast cereals, are fortified with B12.
Functions
The body needs vitamin B12 for a variety of important functions. It is crucial for maintaining the proper functioning of nerves, as well as the production of red blood cells and hemoglobin. It is also necessary for the synthesis of DNA, the genetic material specific for each person that is found in all cells. Since B12 is bound to protein in food, it is released by the action of the stomach acids during digestion. Dietary supplements contain vitamin B12 in its free form, which is readily available for use by the body.
B12 Deficiency
A deficiency of vitamin B12 is rare because the liver can store it in adequate amounts for years. Deficiencies are liable to develop in the elderly, vegetarians and vegans who don't ingest enough B12-containing foods and in people who have pernicious anemia, which causes problems in absorbing B12 due to inflammation of the lining of the stomach. The symptoms of a B12 deficiency include anemia, fatigue, loss of appetite, weight loss, numbness in the hands and feet, confusion and a sore mouth.
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