Vitamin B12: What is it?
What foods provide vitamin B12?
What is the Recommended Dietary
Allowance for vitamin B12 for adults?
When is a deficiency of vitamin
B12 likely to occur?
Who may need a vitamin B12
supplement to prevent a deficiency?
Individuals with pernicious
Individuals with gastrointestinal disorders
Caution: Folic acid may mask
signs of vitamin B12 deficiency
What is the relationship
between vitamin B12, homocysteine, and heart disease?
What is the health risk of too
much vitamin B12?
Selected Food Sources of Vitamin
Table of food sources of vitamin B12
B12 : What is it?
Vitamin B12, also called cobalamin, is important
to good health. It helps maintain healthy nerve cells and red blood cells, and
is also needed to make DNA, the genetic material in all cells (1-4). Vitamin
B12 is bound to the protein in food. Hydrochloric acid in the stomach releases
B12 from protein during digestion. Once released, B12 combines with a substance
called intrinsic factor (IF) before it is absorbed into the bloodstream.
foods provide vitamin B12?
Vitamin B12 is naturally found in animal foods
including fish, milk and milk products, eggs, meat, and poultry. Fortified breakfast
cereals are an excellent source of vitamin B12 and a particularly valuable source
for vegetarians (5, 6, 7). The table of selected food sources of vitamin B12
suggests dietary sources of vitamin B12.
is the Recommended Dietary Allowance for vitamin B12 for adults?
The Recommended Dietary Allowance (RDA) is the
average daily dietary intake level that is sufficient to meet the nutrient requirements
of nearly all (97 to 98 percent) healthy individuals in each life-stage and
gender group (7). The 1998 RDAs for vitamin B12 (in micrograms) for adults (7)
|| 2.8 mcg
of two national surveys, the National Health and Nutrition Examination Survey
(NHANES III-1988-91) (8) and the Continuing Survey of Food Intakes by Individuals
(CSFII 1994-96) (7) found that most adult men and women consume recommended
amounts of vitamin B12 (6-8).
is a deficiency of vitamin B12 likely to occur?
Diets of most
adult Americans provide recommended intakes of
vitamin B12, but deficiency may
still occur as a result of an inability to absorb B12 from food. It can also
occur in individuals with dietary patterns that exclude animal or fortified
foods (9). 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 (10). Sometimes the only symptom of these intestinal disorders
is anemia resulting from B12 deficiency.
Characteristic signs of
B12 deficiency include fatigue, weakness, nausea, constipation, flatulence (gas),
loss of appetite, and weight loss (1, 3, 11). Deficiency also can lead to neurological
changes such as numbness and tingling in the hands and feet (7, 12). Additional
symptoms of B12 deficiency are difficulty in maintaining balance, depression,
confusion, poor memory, and soreness of the mouth or tongue (13). Some of these
symptoms can also 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.
may need a vitamin B12 supplement to prevent a deficiency?
with pernicious anemia
is a form of anemia that occurs when there is an absence of intrinsic factor,
a substance normally present in the stomach.
Vitamin B12 binds with intrinsic
factor before it is absorbed and used by your body (7,14,15). An absence of
intrinsic factor prevents normal absorption of B12 and results in pernicious
Anyone with pernicious anemia
usually needs intramuscular (IM) injections (shots) of vitamin B12. It is very
important to remember that pernicious anemia is a chronic condition that should
be monitored by a physician. Anyone with pernicious anemia has to take lifelong
supplemental vitamin B12.
with gastrointestinal disorders
stomach and small intestinal disorders may not absorb enough
vitamin B12 from
food to maintain healthy body stores (16). Sprue and celiac disease are intestinal
disorders caused by intolerance to protein in wheat and wheat products. Regional
enteritis, localized inflammation of the stomach or small intestine, also results
in generalized malabsorption of vitamin B12 (7). Excess bacteria in the stomach
and small intestine also can decrease vitamin B12 absorption.
Surgical procedures of
the gastrointestinal tract such as surgery to remove all or part of the stomach
often result in a loss of cells that secrete stomach acid and intrinsic factor
(7, 17, 18). Surgical removal of the distal ileum, a section of the intestines,
also can result in the inability to absorb
B12. Anyone who has had either of
these surgeries usually requires lifelong supplemental B12 to prevent a deficiency.
Vitamin B12 must be separated from protein in food before it can bind with
intrinsic factor and be absorbed by your body. Bacterial overgrowth in the stomach
and/or atrophic gastritis, an inflammation of the stomach, contribute to vitamin
B12 deficiency in adults by limiting secretions of stomach acid needed to separate
vitamin B12 from protein in food (10, 20-24). Adults 50 years of age and older
with these conditions are able to absorb the B12 in fortified foods and dietary
supplements. Health care professionals may advise adults over the age of 50
to get their vitamin B12 from a dietary supplement or from foods fortified with
vitamin B12 because 10 to 30 percent of older people may be unable to absorb
vitamin B12 in food (7, 19).
Vegetarians who do not eat meats, fish, eggs, milk or milk products, or
B12 fortified foods consume no vitamin B12 and are at high risk of developing
a deficiency of vitamin B12 (9, 25). When adults adopt a vegetarian diet, deficiency
symptoms can be slow to appear because it usually takes years to deplete normal
body stores of B12. However, severe symptoms of B12 deficiency, most often featuring
poor neurological development, can show up quickly in children and breast-fed
infants of women who follow a strict vegetarian diet (26).
Fortified cereals are one
of the few plant food sources of vitamin B12, and are an important dietary source
of B12 for vegetarians who consume no eggs, milk or milk products. Vegetarian
adults who do not consume plant foods fortified with vitamin B12 need to consider
taking a B12-containing supplement. Vegetarian mothers should consult with a
pediatrician regarding appropriate vitamin B12 supplementation for their infants
Folic acid may mask signs of vitamin B12 deficiency
Folic acid can
correct the anemia that is caused by vitamin B12 deficiency. Unfortunately,
folic acid will not correct the underlying B12 deficiency (1, 27, 28). Permanent
nerve damage can occur if vitamin B12 deficiency is not treated. Folic acid
intake from food and supplements should not exceed 1,000 micrograms (mcg) daily
because large amounts of folic acid can hide the damaging effects of vitamin
B12 deficiency (7). Adults older than 50 years are advised to consult with their
physician about the advisability of taking folic acid without also taking a
vitamin B12 supplement.
is the relationship between vitamin B12, homocysteine, and heart disease?
A deficiency of
vitamin B12, folate, or vitamin B6 may increase your blood level of homocysteine,
an amino acid normally found in your blood. There is evidence that an elevated
blood level of homocysteine is an independent risk factor for heart disease
and stroke (29-38). The evidence suggests that high levels of homocysteine may
damage coronary arteries (34) or make it easier for blood clotting cells called
platelets to clump together and form a clot. However, there is currently no
evidence available to suggest that lowering homocysteine level with vitamins
will actually reduce your risk of heart disease. Clinical intervention trials
are needed to determine whether supplementation with vitamin B12, folic acid,
or vitamin B6 can help protect you against developing coronary heart disease.
is the health risk of too much vitamin B12?
Vitamin B12 has
a very low potential for toxicity. The Institute of Medicine states that "no
adverse effects have been associated with excess vitamin B12 intake from food
and supplements in healthy individuals (7)." The Institute recommends that adults
over 50 years of age get most of their vitamin B12 from supplements or fortified
food because of the high incidence of impaired absorption of B12 from unfortified
foods in this population (7).
Food Sources of Vitamin B12
As the 2000 Dietary
Guidelines for Americans state, "Different foods contain different nutrients
and other healthful substances. No single food can supply all the nutrients
in the amounts you need" (39). As the following table indicates, vitamin B12
is found naturally in animal foods. It is also found in fortified foods such
as fortified breakfast cereals.
Table of Food
Sources of Vitamin B12 (5)
liver, cooked, 3 oz
cereals, (100%) fortified),
rainbow, cooked, 3 oz
sockeye, cooked, 3 oz
cereals (25% fortified),
cooked, 3 oz
breaded and fried, 3/4 c
breaded and fried, 6 pieces
canned in water, 3 oz
Cheese, 1 oz
cooked, 3 oz
cheese, 1 oz
cheese, 1 oz
|* DV =
Daily Value. DVs are reference numbers based on the Recommended Dietary
Allowance (RDA). They were developed 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 (mcg). The percent DV (%DV) listed on the nutrition facts
panel of food labels tells adults what percentage of the DV is provided
by one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily
Values may be higher or lower depending on your calorie needs. Foods that
provide lower percentages of the DV also contribute to a healthful diet.
This fact sheet was developed
by the Clinical Nutrition Service, Warren Grant Magnuson Clinical Center,
National Institutes of Health (NIH), Bethesda, MD, in conjunction with the
Office of Dietary Supplements (ODS) in the Office of the Director of NIH.
The mission of ODS is to strengthen knowledge and understanding of dietary
supplements by evaluating scientific information, stimulating and supporting
research, disseminating research results, and educating the public to foster
an enhanced quality of life and health for the U.S. population. The Clinical
Nutrition Service and the ODS would like to thank the expert scientific
reviewers for their role in ensuring the scientific accuracy of the information
discussed in this fact sheet.