What is vitamin B12?

Vitamin B₁₂ helps maintain healthy nerve cells and red blood cells . It is also needed to help make DNA, the genetic material in all cells. Vitamin B₁₂ is also called cobalamin because it contains the metal cobalt .

Vitamin B₁₂ is bound to the protein in food. Hydrochloric acid in the stomach releases vitamin B₁₂ from proteins in foods during digestion. Once released, vitamin B₁₂ combines with a substance called intrinsic factor (IF). This complex can then be absorbed by the intestinal tract.

What foods provide vitamin B12?

Vitamin B₁₂ is naturally found in foods that come from animals, including fish, meat, poultry, eggs, milk, and milk products. Fortified breakfast cereals are a particularly valuable source of vitamin B₁₂ for vegetarians . Table 1 lists a variety of food sources of vitamin B₁₂.

Table 1: Selected food sources of vitamin B₁₂

Food	Micrograms (μg) per serving	Percent DV*
Mollusks, clam, mixed species, cooked, 3 ounces	84.1	1400
Liver, beef, braised, 1 slice	47.9	780
Fortified breakfast cereals, (100%) fortified), ¾ cup	6.0	100
Trout, rainbow, wild, cooked, 3 ounces	5.4	90
Salmon, sockeye, cooked, 3 ounces	4.9	80
Trout, rainbow, farmed, cooked, 3 ounces	4.2	50
Beef, top sirloin, lean, choice, broiled, 3 ounces	2.4	40
Fast Food, Cheeseburger, regular, double patty & bun, 1 sandwich	1.9	30
Fast Food, Taco, 1 large	1.6	25
Fortified breakfast cereals (25% fortified), ¾ cup	1.5	25
Yogurt, plain, skim, with 13 grams protein per cup, 1 cup	1.4	25
Haddock, cooked, 3 ounces	1.2	20
Clams, breaded & fried, ¾ cup	1.1	20
Tuna, white, canned in water, drained solids, 3 ounces	1.0	15
Milk, 1 cup	0.9	15
Pork, cured, ham, lean only, canned, roasted, 3 ounces	0.6	10
Egg, whole, hard boiled, 1	0.6	10
American pasteurized cheese food, 1 ounces	0.3	6
Chicken, breast, meat only, roasted, ½ breast	0.3	6

*DV = Daily Value. DVs are reference numbers developed by the Food and Drug Administration (FDA) to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for vitamin B₁₂ is 6.0 micrograms (μg). Most food labels do not list a food's vitamin B₁₂ content. The percent DV (%DV) listed on the table indicates the percentage of the DV provided in one serving. A food providing 5% of the DV or less is a low source while a food that provides 10% to 19% of the DV is a good source. A food that provides 20% or more of the DV is high in that nutrient. It is important to remember that foods that provide lower percentages of the DV also contribute to a healthful diet.

What is the recommended dietary intake for vitamin B12?

Recommendations for vitamin B₁₂ are provided in the Dietary Reference Intakes (DRIs) developed by the Institute of Medicine of the National Academies. Dietary Reference Intakes is the general term for a set of reference values used for planning and assessing nutrient intake for healthy people. Three important types of reference values included in the DRIs are Recommended Dietary Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL). The RDA recommends the average daily intake that is sufficient to meet the nutrient requirements of nearly all (97% to 98%) healthy individuals in each age and gender group. An AI is set when there is insufficient scientific data available to establish an RDA. AIs meet or exceed the amount needed to maintain a nutritional state of adequacy in nearly all members of a specific age and gender group. The UL, on the other hand, is the maximum daily intake unlikely to result in adverse health effects. Table 2 lists the RDAs for vitamin B₁₂, in micrograms, for children and adults.

Table 2: Recommended Dietary Allowances (RDA) for vitamin B₁₂ for children and adults

Age (years)	Males and Females (μg/day)	Pregnancy (μg/day)	Lactation (μg/day)
1-3	0.9	N/A	N/A
4-8	1.2	N/A	N/A
9-13	1.8	N/A	N/A
14-18	2.4	2.6	2.8
19 and older	2.4	2.6	2.8

Information on vitamin B₁₂ is insufficient to establish an RDA for infants. Therefore, an AI has been established that is based on the amount of vitamin B₁₂ consumed by healthy infants who are fed breast milk . Table 3 lists the AIs for vitamin B₁₂, in micrograms, for infants.

Table 3: Adequate Intake (AI) for vitamin B₁₂ for infants

Age (months)	Males and Females (μg/day)
0-6 months	0.4
7-12 months	0.5

When is a deficiency of vitamin B12 likely to occur?

Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III-1988-94) and the Continuing Survey of Food Intakes by Individuals (CSFII 1994-96) found that most children and adults in the United States (US) consume recommended amounts of vitamin B₁₂ . A deficiency may still occur as a result of an inability to absorb vitamin B₁₂ from food and in strict vegetarians who do not consume any foods that come from animals. As a general rule, most individuals who develop a vitamin B₁₂ deficiency have an underlying stomach or intestinal disorder that limits the absorption of vitamin B₁₂ . Sometimes the only symptom of these intestinal disorders is subtly reduced cognitive function resulting from early vitamin B₁₂ deficiency. Anemia and dementia follow later.

Signs, symptoms, and health problems associated with vitamin B₁₂ deficiency:

Characteristic signs, symptoms, and health problems associated with vitamin B₁₂ deficiency include anemia, fatigue, weakness, constipation, loss of appetite, and weight loss.

Deficiency also can lead to neurological changes such as numbness and tingling in the hands and feet .

Additional symptoms of vitamin B₁₂ deficiency are difficulty in maintaining balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue.

Signs of vitamin B₁₂ deficiency in infancy include failure to thrive, movement disorders, delayed development, and megaloblastic anemia.

Many of these symptoms are very general and can result from a variety of medical conditions other than vitamin B₁₂ deficiency. It is important to have a physician evaluate these symptoms so that appropriate medical care can be given.