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Vitamin B12 is also called cobalamin because it contains
the metal cobalt. This vitamin 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 bound
to the protein in food. Hydrochloric acid in the stomach
releases B12 from proteins in foods during digestion. Once
released, vitamin B12 combines with a substance called gastric
intrinsic factor. This complex can then be absorbed by the
intestinal tract.
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 (U.S.)
consume recommended amounts of vitamin B12. A deficiency
may still occur as a result of an inability to absorb B12
from food and in strict vegetarians who do not consume any
animal foods. 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 B12 deficiency.
Anemia and dementia follow later.
Characteristic
signs, symptoms, and health problems associated with 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 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.
B12
Information from NIH. Elderly, Anemic etc.
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Dietary Supplement Fact Sheet: Vitamin B12
Office of Dietary Supplements • NIH Clinical Center • National
Institutes of Health
Table of Contents
What is vitamin B12?
What foods provide vitamin B12?
What is the recommended dietary intake for vitamin B12?
When is a deficiency of vitamin B12 likely to occur?
Do pregnant and/or lactating women need extra Vitamin B12?
Who else may need a vitamin B12 supplement to prevent a
deficiency?
Drug : Nutrient Interactions
Caution: Folic Acid and vitamin B12 deficiency
What is the relationship between vitamin B12 homocysteine,
and cardiovascular disease?
Do healthy young adults need a vitamin B12 supplement?
What is the health risk of too much vitamin B12?
Selecting a healthful diet
References
Reviewers
What is vitamin B12?
Vitamin B12 is also called cobalamin because it contains
the metal cobalt. This vitamin helps maintain healthy nerve
cells and red blood cells [1-4]. It is also needed to help
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 proteins in foods
during digestion. Once released, vitamin B12 combines with
a substance called gastric intrinsic factor (IF). This complex
can then be absorbed by the intestinal tract.
What foods provide vitamin B12?
Vitamin B12 is naturally found in animal foods including
fish, meat, poultry, eggs, milk, and milk products. Fortified
breakfast cereals are a particularly valuable source of
vitamin B12 for vegetarians [5-7]. Table 1 lists a variety
of food sources of vitamin B12.
Table 1: Selected food sources
of vitamin B12 [5]
FoodMicrograms
(?g)
per serving Percent
DV*Mollusks, clam, mixed species, cooked, 3 ounces 84.11400Liver,
beef, braised, 1 slice47.9780Fortified breakfast cereals,
(100%) fortified), ¾ cup6.0100Trout, rainbow, wild,
cooked, 3 ounces5.490Salmon, sockeye, cooked, 3 ounces4.980Trout,
rainbow, farmed, cooked, 3 ounces4.250Beef, top sirloin,
lean, choice, broiled, 3 ounces2.440Fast Food, Cheeseburger,
regular, double patty & bun, 1 sandwich1.930Fast Food,
Taco, 1 large1.625Fortified breakfast cereals (25% fortified),
¾ cup1.525Yogurt, plain, skim, with 13 grams protein
per cup, 1 cup1.425Haddock, cooked, 3 ounces1.220Clams,
breaded & fried, ¾ cup1.120Tuna, white, canned
in water, drained solids, 3 ounces1.015Milk, 1 cup0.915Pork,
cured, ham, lean only, canned, roasted, 3 ounces0.610Egg,
whole, hard boiled, 10.610American pasteurized cheese food,
1 ounces0.36Chicken, breast, meat only, roasted, ½
breast0.36
*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 (?g). 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 10-19%
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. For foods not
listed in this table, please refer to the U.S. Department
of Agriculture's Nutrient Database Web site: http://www.nal.usda.gov/
fnic/cgi-bin/nut_search.pl.
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 Academy of Sciences [7]. 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 (97-98%)
healthy individuals in each age and gender group [7]. An
AI is set when there is insufficient scientific data available
to establish a 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 [7]. The UL,
on the other hand, is the maximum daily intake unlikely
to result in adverse health effects [7]. Table 2 lists the
RDAs for vitamin B12, in micrograms (?g), for children and
adults.
Table
2: Recommended Dietary Allowances (RDA) for vitamin B12
for children and adults [7]
Age
(years)Males and Females
(?g/day) Pregnancy
(?g/day)Lactation
(?g/day)1-30.9N/AN/A4-81.2N/AN/A9-
131.8N/AN/A14-182.42.62.819
and older2.42.62.8
There is insufficient information
on vitamin B12 to establish a RDA for infants. Therefore,
an Adequate Intake (AI) has been established that is based
on the amount of vitamin B12 consumed by healthy infants
who are fed breast milk [7]. Table 3 lists the Adequate
Intakes for vitamin B12, in micrograms (?g), for infants.
Table 3: Adequate Intake
for vitamin B12 for infants [7]
Age
(months)Males and Females
(?g/day) 0-6 months0.47-12 months0.5
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) [8] and
the Continuing Survey of Food Intakes by Individuals (CSFII
1994-96) found that most children and adults in the United
States (U.S.) consume recommended amounts of vitamin B12
[6-8]. A deficiency may still occur as a result of an inability
to absorb B12 from food and in strict vegetarians who do
not consume any animal 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 subtly reduced cognitive
function resulting from early B12 deficiency. Anemia and
dementia follow later [1,11].
Signs, symptoms, and health
problems associated with vitamin B12 deficiency
* Characteristic signs, symptoms, and health problems associated
with B12 deficiency include anemia, fatigue, weakness, constipation,
loss of appetite, and weight loss [1,3,12].
* Deficiency also can lead to neurological changes such
as numbness and tingling in the hands and feet [7,13].
* Additional symptoms of B12 deficiency are difficulty in
maintaining balance, depression, confusion, dementia, poor
memory, and soreness of the mouth or tongue [14].
* Signs of vitamin B12 deficiency in infancy include failure
to thrive, movement disorders, delayed development, and
megaloblastic anemia [15].
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.
Do pregnant and/or lactating women need extra Vitamin B12?
During pregnancy, nutrients travel from mother to fetus
through the placenta. Vitamin B12, like other nutrients,
is transferred across the placenta during pregnancy. Breast-fed
infants receive their nutrition, including vitamin B12,
through breast milk. Vitamin B12 deficiency in infants is
rare but can occur as a result of maternal insufficiency
[15]. For example, breast-fed infants of women who follow
strict vegetarian diets have very limited reserves of vitamin
B12 and can develop a vitamin B12 deficiency within months
of birth [7,16]. This is of particular concern because undetected
and untreated vitamin B12 deficiency in infants can result
in permanent neurologic damage. Consequences of such neurologic
damage are severe and can be irreversible. Mothers who follow
a strict vegetarian diet should consult with a pediatrician
regarding appropriate vitamin B12 supplementation for their
infants and children [7]. They should also discuss their
own need for vitamin B12 supplementation with their personal
physician.
Who else may need a vitamin B12 supplement to prevent a
deficiency?
* Individuals with pernicious anemia or with gastrointestinal
disorders may benefit from or require a vitamin B12 supplement.
* Older adults and vegetarians may benefit from a vitamin
B12 supplement or an increased intake of foods fortified
with vitamin B12.
* Some medications may decrease absorption of vitamin B12.
Chronic use of those medications may result in a need for
supplemental B12.
Individuals with pernicious
anemia
Anemia is a condition that occurs when there is insufficient
hemoglobin in red blood cells to carry oxygen to cells and
tissues. Common signs and symptoms of anemia include fatigue
and weakness. Anemia can result from a variety of medical
problems, including deficiencies of vitamin B12, vitamin
B6, folate and iron. Pernicious anemia is the name given
more than a century ago to describe the then-fatal vitamin
B12 deficiency anemia that results from severe gastric atrophy,
a condition that prevents gastric cells from secreting intrinsic
factor. Intrinsic factor is a substance normally present
in the stomach. Vitamin B12 must bind with intrinsic factor
before it can be absorbed and used by your body [7,17-18].
An absence of intrinsic factor prevents normal absorption
of B12 and results in pernicious anemia.
Most individuals with pernicious
anemia need parenteral (deep subcutaneous) injections (shots)
of vitamin B12 as initial therapy to replenish depleted
body B12 stores. Body stores of vitamin B12 can then be
managed by a daily oral supplement of B12. A physician will
manage the treatment required to maintain the vitamin B12
status of individuals with pernicious anemia.
Individuals
with gastrointestinal disorders
Individuals with stomach and small intestinal disorders
may be unable to absorb enough vitamin B12 from food to
maintain healthy body stores [19]. Intestinal disorders
that may result in malabsorption of vitamin B12 include:
* Sprue, often referred to as Celiac Disease (CD), is a
genetic disorder. People with CD are intolerant to a protein
called gluten. In CD, gluten can trigger damage to the small
intestines, where most nutrient absorption occurs. People
with CD often experience nutrient malabsorption. They need
to follow a gluten free diet to avoid malabsorption and
other symptoms of CD.
* Crohn's Disease is an inflammatory bowel disease that
affects the small intestines. People with Crohn's disease
often experience diarrhea and nutrient malabsorption.
* Surgical procedures in 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 [7,20-21]. Surgical removal of the distal ileum,
a section of the intestines, also can result in the inability
to absorb vitamin B12. Anyone who has had either of these
surgeries usually requires lifelong supplemental B12 to
prevent a deficiency. These individuals would be under the
routine care of a physician, who would periodically evaluate
vitamin B12 status and recommend appropriate treatment.
Older adults
Gastric acid helps release vitamin B12 from the protein
in food. This must occur before B12 binds with intrinsic
factor and is absorbed in your intestines. Atrophic gastritis,
which is an inflammation of the stomach, decreases gastric
secretion. Less gastric acid decreases the amount of B12
separated from proteins in foods and can result in poor
absorption of vitamin B12 [10,22-26]. Decreased gastric
secretion also results in overgrowth of normal bacterial
flora in the small intestines. The bacteria may take up
vitamin B12 for their own use, further contributing to a
vitamin B12 deficiency [27].
Up to 30 percent of adults
50 years and older may have atrophic gastritis, an overgrowth
of intestinal flora, and be unable to normally absorb vitamin
B12 in food. They are, however, able to absorb the synthetic
B12 added to fortified foods and dietary supplements. Vitamin
supplements and fortified foods may be the best sources
of vitamin B12 for adults over the age of 50 [7].
Researchers have long been
interested in the potential connection between vitamin B12
deficiency and dementia [28]. A recent review examined correlations
between cognitive skills, homocysteine levels, and blood
levels of folate, vitamin B12 and vitamin B6. The authors
suggested that vitamin B12 deficiency may decrease levels
of substances needed for the metabolism of neurotransmitters
[29]. Neurotransmitters are chemicals that transmit nerve
signals. Reduced levels of neurotransmitters may result
in cognitive impairment. In 142 individuals considered at
risk for dementia, researchers found that a daily supplement
providing 2 milligrams (mg) folic acid and 1 mg B12, taken
for 12 weeks, lowered homocysteine levels by 30%. They also
demonstrated that cognitive impairment was significantly
associated with elevated plasma total homocysteine. However,
the decrease in homocysteine levels seen with vitamin supplementation
did not improve cognition [30]. It is too soon to make any
recommendations, but is an intriguing area of research.
Vegetarians
The popularity of vegetarian diets has risen along with
an interest in avoiding meat and meat products for environmental,
philosophical, and health reasons. However, the term vegetarianism
is subject to a wide range of interpretations. Some people
consider themselves to be vegetarian when they avoid red
meat. Others believe that vegetarianism requires avoidance
of all animal products, including meat, poultry, fish, eggs,
and dairy foods. The most commonly described forms of vegetarianism
include:
* "Lacto-ovo vegetarians", who avoid meat, poultry,
and fish products but consume eggs and dairy foods
* "Strict vegetarians", who avoid meat, poultry,
fish, eggs, and dairy foods
* "Vegans", who avoid meat, poultry, fish, eggs,
and dairy foods but also do not use animal products such
as honey, leather, fur, silk, and wool
Strict vegetarians and vegans
are at greater risk of developing vitamin B12 deficiency
than lacto-ovo vegetarians and non-vegetarians because natural
food sources of vitamin B12 are limited to animal foods
[7]. Fortified cereals are one of the few sources of vitamin
B12 from plants, and are an important dietary source of
B12 for strict vegetarians and vegans. Strict vegetarians
and vegans who do not consume plant foods fortified with
vitamin B12 need to consider taking a dietary supplement
that contains vitamin B12 and should discuss the need for
B12 supplementation with their physician.
There is wide belief that
vitamin B12 can be consistently obtained from nutritional
yeasts. Consumers should be aware that these products may
or may not contain added nutrients such as vitamin B12.
Dietary supplements are regulated as foods rather than drugs,
and companies that sell supplements such as nutritional
yeasts fortified with vitamin B12 can legally change their
formulation at any time. If you choose to supplement, select
reliable sources of vitamin B12 and read product labels
carefully.
When adults adopt a strict
vegetarian diet, deficiency symptoms can be slow to appear.
It may take years to deplete normal body stores of B12.
However, breast-fed infants of women who follow strict vegetarian
diets have very limited reserves of vitamin B12 and can
develop a vitamin B12 deficiency within months [7]. This
is of particular concern because undetected and untreated
vitamin B12 deficiency in infants can result in permanent
neurologic damage. Consequences of such neurologic damage
are severe and can be irreversible. There are many case
reports in the literature of infants and children who suffered
consequences of vitamin B12 deficiency. It is very important
for mothers who follow a strict vegetarian diet to consult
with a pediatrician regarding appropriate vitamin B12 supplementation
for their infants and children [7].
Drug : Nutrient Interactions
Table 4 summarizes several drugs that potentially influence
vitamin B12 absorption.
Table 4: Important vitamin
B12/drug interactions
DrugPotential Interaction* Proton Pump Inhibitors (PPIs)
are used to treat gastroesophageal reflux disease (GERD)
and peptic ulcer disease. Examples of PPIs are Omeprazole
(Prilosec©) and Lansoprazole (Prevacid©)PPI medications
can interfere with vitamin B12 absorption from food by slowing
the release of gastric acid into the stomach [31-33]. This
is a concern because acid is needed to release vitamin B12
from food prior to absorption. So far, however, there is
no evidence that these medications promote vitamin B12 deficiency,
even after long-term use [34].* H2 receptor antagonists
are used to treat peptic ulcer disease. Examples are Tagament©,
Pepsid©, and Zantac©H2 receptor antagonists can
interfere with vitamin B12 absorption from food by slowing
the release of gastric acid into the stomach. This is a
concern because acid is needed to release vitamin B12 from
food prior to absorption. So far, however, there is no evidence
that these medications promote vitamin B12 deficiency, even
after long-term use [34].* Metformin© is a drug used
to treat diabetes.Metformin© may interfere with calcium
metabolism [35]. This may indirectly reduce vitamin B12
absorption because vitamin B12 absorption requires calcium
[35]. Surveys suggest that from 10% to 30% of patients taking
Metformin© have evidence of reduced vitamin B12 absorption
[35].
In a study involving 21
subjects with type 2 diabetes, researchers found that 17
who were prescribed Metformin© experienced a decrease
in vitamin B12 absorption. Researchers also found that supplementation
with calcium carbonate (1200 milligrams per day) helped
limit the effect of Metformin© on vitamin B12 absorption
in these individuals [35].
Although
these medications may interact with the absorption of vitamin
B12, they are necessary to take for certain conditions.
It is important to consult with a physician and registered
dietitian to discuss the best way to maintain vitamin B12
status when taking these medications.
Caution: Folic Acid and vitamin B12 deficiency
Folic acid can correct the anemia that is caused by vitamin
B12 deficiency. Unfortunately, folic acid will not correct
the nerve damage also caused by B12 deficiency [1,36]. 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 (?g) daily in healthy individuals
because large amounts of folic acid can trigger the damaging
effects of vitamin B12 deficiency [7]. Adults older than
50 years who take a folic acid supplement should ask their
physician or qualified health care provider about their
need for vitamin B12 supplementation.
What is the relationship between vitamin B12 homocysteine,
and cardiovascular disease?
Cardiovascular disease involves any disorder of the heart
and blood vessels that make up the cardiovascular system.
Coronary heart disease occurs when blood vessels which supply
the heart become clogged or blocked, increasing the risk
of a heart attack. Vascular damage can also occur to blood
vessels supplying the brain, and can result in a stroke.
Cardiovascular disease is
the most common cause of death in industrialized countries
such as the U.S., and is on the rise in developing countries.
The National Heart, Lung, and Blood Institute of the National
Institutes of Health has identified many risk factors for
cardiovascular disease, including an elevated LDL-cholesterol
level, high blood pressure, a low HDL-cholesterol level,
obesity, and diabetes [37]. In recent years, researchers
have identified another risk factor for cardiovascular disease,
an elevated homocysteine level. Homocysteine is an amino
acid normally found in blood, but elevated levels have been
linked with coronary heart disease and stroke [38-47]. Elevated
homocysteine levels may impair endothelial vasomotor function,
which determines how easily blood flows through blood vessels.
High levels of homocysteine also may damage coronary arteries
and make it easier for blood clotting cells called platelets
to clump together a form a clot, which may lead to a heart
attack [43].
Vitamin B12, folate, and
vitamin B6 are involved in homocysteine metabolism. In fact,
a deficiency of vitamin B12, folate, or vitamin B6 may increase
blood levels of homocysteine. Recent studies found that
supplemental vitamin B12 and folic acid decreased homocysteine
levels in subjects with vascular disease and in young adult
women. The most significant drop in homocysteine level was
seen when folic acid was taken alone [48-49]. A significant
decrease in homocysteine levels also occurred in older men
and women who took a multivitamin/ multimineral supplement
for 56 days [50]. The supplement taken provided 100% of
Daily Values (DVs) for nutrients in the supplement.
Evidence
supports a role for supplemental folic acid and vitamin
B12 for lowering homocysteine levels, however this does
not mean that these supplements will decrease the risk of
cardiovascular disease. Clinical intervention trials are
underway to determine whether supplementation with folic
acid, vitamin B12, and vitamin B6 can lower risk of coronary
heart disease. It is premature to recommend vitamin B12
supplements for the prevention of heart disease until results
of ongoing randomized, controlled clinical trials positively
link increased vitamin B12 intake from supplements with
decreased homocysteine levels AND decreased risk of cardiovascular
disease.
Do healthy young adults need a vitamin B12 supplement?
It is generally accepted that older adults are at greater
risk of developing a vitamin B12 deficiency than younger
adults. One study, however, suggests that the prevalence
of B12 deficiency in young adults may be greater than previously
thought. This study found that the percentage of subjects
in three age groups (26 to 49y, 50 to 64y, and 65y and older)
with deficient blood levels of vitamin B12 was similar across
all age groups but that symptoms of B12 deficiency were
not as apparent in younger adults. This study also suggested
that those who did not take a supplement containing vitamin
B12 were twice as likely to be B12 deficient as supplement
users, regardless of age group. However, non-supplement
users who consumed fortified cereal more than 4 times per
week did appear to be protected from deficient blood levels
of B12. Better tools and standards to diagnose B12 deficiencies
are needed to make specific recommendations about the appropriateness
of vitamin B12 supplements for younger adults [51].
What is the health risk of too much vitamin B12?
The Institute of Medicine of the National Academy of Sciences
did not establish a Tolerable Upper Intake Level for this
vitamin because 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]. In fact, the Institute recommends that adults over
50 years of age get most of their vitamin B12 from vitamin
supplements or fortified food because of the high incidence
of impaired absorption of B12 from animal foods in this
age group [7].
Selecting a healthful diet
As the 2000 Dietary Guidelines for Americans states, "Different
foods contain different nutrients and other healthful substances.
No single food can supply all the nutrients in the amounts
you need" [52]. For more information about building
a healthful diet, refer to the Dietary Guidelines for Americans
http://www.usda.gov/cnpp/DietGd.pdf [52] and the US Department
of Agriculture's Food Guide Pyramid http://www.nal.usda.gov/fnic/Fpyr/pyramid.html
[53].
About ODS and the NIH Clinical CenterGeneral Safety AdvisoryDisclaimerPrint-friendly
version
Posted Date:
10/7/2004Updated:
5/25/2005 6:31 PM
References
1.
Herbert V. Vitamin B12 in Present Knowledge in Nutrition.
17th ed. Washington, D.C.: International Life Sciences Institute
Press, 1996.
2. Herbert V and Das K. Vitamin B12 in Modern Nutrition
in health and disease. 8th ed. Baltimore: Williams &
Wilkins, 1994.
3. Combs G. Vitamin B12 in The Vitamins. New York: Academic
Press, Inc, 1992.
4. Zittoun J and Zittoun R. Modern clinical testing strategies
in cobalamin and folate deficiency. Sem Hematol 1999;36:35-46.
[PubMed abstract]
5. U.S. Department of Agriculture, Agricultural Research
Service. 2003. USDA Nutrient Database for Standard Reference,
Release 16. Nutrient Data Laboratory Home Page, http://www.nal.usda.gov/fnic/cgi-bin/nut_search.pl.
http://www.wonderlabs.com/
sublingual-b12/index.html