Vitamin B12 is a water-soluble vitamin. Water-soluble vitamins dissolve in water. After the body uses these vitamins, leftover amounts leave the body through the urine.

Typically, water-soluble vitamins can not be stored by the body. Vitamin B12 is special, because the body can store it for years in the liver. Because of this, a vitamin B12 deficience is very rare.

Vitamin B12, like the other B vitamins, is important for metabolism. It helps in the formation of red blood cells and in the maintenance of the central nervous system.

Vitamin B12 is found in eggs, meat, poultry, shellfish, milk, and milk products.

Vitamin B12 deficiencies occur when the body is unable to properly use the vitamin. Pernicious anemia can make the body unable to absorb vitamin B12 from the intestinal tract.

Because vitamin B12 comes primarily from animal products, people who follow a strict vegetarian or vegan diet and do not consume eggs or dairy products may require vitamin B12 supplements. (Non-animal sources of vitamin B12 exist but are highly variable in their B12 content. They are considered unreliable sources of the vitamin.)

Those who had surgery on specific parts of the small intestine or stomach are also prone to a deficiency if they do not take B12 supplements.

Low levels of B12 can cause anemia, numbness or tingling in the arms and legs, weakness, and loss of balance.

Recommended dietary allowances (RDAs) are defined as the levels of intake of essential nutrients that, on the basis of scientific knowledge, the Food and Nutrition Board believes meets the known nutrient needs of practically all healthy persons.

The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods from the food guide pyramid.

Specific recommendations for each vitamin depend on age, gender, and other factors (such as pregnancy).

Goldman L, Ausiello D. Cecil Textbook of Medicine. 22nd ed. Philadelphia, Pa: WB Saunders; 2004.

Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes: Thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline. Washington, DC: National Academy Press; 1998.