pregnant women: RDA 2.6 mcg;
breastfeeding women: RDA 2.8 mcg
Sources of vitamin B 12
Vitamin B 12 is found in food that comes from
animals, including meat, fish, poultry, eggs, milk,
and cheese. It is also added to fortified breakfast cere-
als and is found in some fermented bean products.
Heating or cooking foods does not reduce their vita-
min B 12 content very much.
The following list gives the approximate vitamin
B 12 content for some common foods:
calf’s liver, cooked, 4 ounces: 41 mcg
salmon, baked or broiled, 4 ounces: 3.3 mcg
shrimp, steamed or boiled, 4 ounces: 1.7 mcg
mollusks or clams, cooked, 3 ounces: 84 mcg
tuna, white, canned in water, 3 ounces: 1.0 mcg
beef, top sirloin, broiled, 3 ounces: 2.4 mcg
cheeseburger, fast food, double patty: 1.9 mcg
taco, fast food, 1 large: 1.6 mcg
ham, canned or roasted, 3 ounces: 0.6 mcg
chicken breast, roasted, 1/2 breast: 0.3mcg
milk, 1 cup: 0.9 mcg
egg, 1 whole, cooked: 0.3 mcg
breakfast cereal, fortified 100%, 3/4 cup: 6.0 mcg
breakfast cereal, fortified 25%, 3/4 cup: 1.5 mcg
Vitamin B 12 deficiency
Vitamin B 12 deficiency is hard to determine, and
there is little agreement on how many people are vita-
min B 12 deficient. This is partly because the body can
store 5–10 year’s worth of vitamin B 12 , so symptoms of
deficiency are slow to show up, especially in adults.
Researchers estimate that anywhere from 300,000–3
million Americans are vitamin B 12 deficient.
Most meat-eating Americans get enough vitamin
B 12 from diet alone. However, the elderly are at higher
risk than younger people of developing mild vitamin
B 12 deficiency. Other people at greater risk of vitamin
B 12 deficiency include:
vegans who eat no animal products
breastfed babies of vegan mothers
people who have had part of their stomach or intes-
tine removed
people with diseases that interfere with the absorp-
tion of nutrients such as Crohn’s disease, celiac dis-
ease, or ulcerative colitis.
people with alcoholism
people with liver or kidney damage
people with HIV/AIDS
Symptoms of vitamin B 12 deficiency include shaky
movements, loss of balance, muscle weakness and
spasms, vision problems, reduced mental functioning,
and changes in mood and mental state. These symp-
toms are quite general and have many other causes
besides vitamin B 12 deficiency.PrecautionsBreast-fed infants of strict vegan mothers are par-
ticularly likely to develop vitamin B 12 deficiency, as
they have little or no B 12 stored in their bodies at birth.
Failure to get enough B 12 during the infancy and child-
hood can result in permanent damage to the nervous
system. Vegan mothers should consult a pediatrician
about appropriate Vitamin B 12 supplementation.
Individuals with the eye disorder Leber’s optic
atrophy should not use vitamin B 12 supplements.
High levels of B 12 will accelerate degeneration of the
optic nerve, leading to blindness.
Folic acid may mask vitamin B 12 deficiency. Folic
acid supplements will reverse anemia symptoms, but
they do not stop nerve damage caused by B 12 defi-
ciency. Permanent nerve damage may result. People
with suspected folic acid deficiency who begin taking
folic acid supplements should also be evaluated for
vitamin B 12 deficiency.KEY TERMS
Amino acid—Molecules that are the basic building
blocks of proteins.
Dietary supplement—A product, such as a vitamin,
mineral, herb, amino acid, or enzyme, that is
intended to be consumed in addition to an individ-
ual’s diet with the expectation that it will improve
health.
Enzyme—A protein that change the rate of a chem-
ical reaction within the body without themselves
being used up in the reaction.
Vitamin—A nutrient that the body needs in small
amounts to remain healthy but that the body cannot
manufacture for itself and must acquire through
diet.
Water-soluble vitamin—A vitamin that dissolves in
water and can be removed from the body in urine.Vitamin B12