Vitamin B12 is a water-soluble vitamin in the B-complex of vitamins. Most people obtain adequate vitamin B12 from the foods they eat, but some people still choose to supplement, or your doctor may recommend a supplement. Unlike some vitamins, vitamin B12 is measured in micrograms, not milligrams. A micrograms is a thousandth of a milligram, so 500 mg of vitamin B12 is 500,000 micrograms; the recommended daily intake is between 2 and 2.8 micrograms.
Overview of Vitamin B12
The body uses vitamin B12, along with the B-complex vitamin folate, to help produce DNA. B12 also helps to keep levels of some amino acids stable and to prevent damage to your nerve cells. Found primarily in animal products such as fish, poultry, eggs, milk and other dairy products, B12 is also used to enrich some grain products. According to the University of Florida, adults who are not pregnant or breastfeeding require 2.4 micrograms of B12 a day, while pregnant women should get 2.6 micrograms and women who are breastfeeding should get 2.8 micrograms. You usually can get these amounts in your daily diet.
Vitamin B12 Deficiency
While vitamin B12 deficiency is generally rare in healthy adults, occasionally strict vegetarians, older adults or people whose bodies do not properly process vitamin B12 may suffer from a deficiency. According to the National Institutes of Health, situations in which your physician may check to see if you have a vitamin B12 deficiency include when another condition called megaloblastic anemia is suspected, if you have been suffering from delirium or dementia, if you suffer from a disorder like celiac or Crohn's disease, or sometimes if you are pregnant. Vitamin B12 deficiency is usually treated by supplements of B12, either in pill form or as injections.
Vitamin B12 and Anemia
A deficiency of vitamin B12 can contribute to your developing a type of anemia called megaloblastic or pernicious anemia. Because vitamin B12 is used in the production of red blood cells and the maintenance of the nervous system, a lack of B12 can cause your body to manufacture inadequate red blood cells. Pernicious anemia may have no symptoms and occurs most frequently in people who suffer either from an autoimmune disorder or who have a disease of malabsorption that prevents their bodies from absorbing enough vitamin B12. Treatment for this type of anemia depends on its severity, but usually involves B12 supplements.
Contraindications of Vitamin B12
While vitamin B12 is naturally found in many foods, there are some situations in which you should not take supplements or high doses of vitamin B12. If you have Leber's disease, large doses of vitamin B12 could lead to damage in your optic nerve and even blindness. If you have an allergy to cobalt, you should avoid vitamin B12 supplements until you have discussed it with your physician. Let your doctor know if you are pregnant or breastfeeding, and discuss any other medications or supplements you are taking.