nonheme iron, and its rate of absorption is less influ-
enced by other foods that simultaneously are present
in the digestive system.
The following list gives the approximate iron con-
tent for some common sources of heme iron:
chicken liver, cooked, 3 ounces: 12.8 mg
beef, cooked, 3 ounces: 3.2 mg
turkey light meat, cooked, 3 ounces: 2.3 mg
chicken dark meat, cooked, 3 ounces: 1.13 mg
pork loin, cooked, 3 ounces: 0.8 mg
oysters, 6 medium: 5.04 mg
shrimp, cooked, 8 large: 1.36 mg
tuna, light, canned, 3 ounces: 1.3 mg
halibut, cooked, 3 ounces: 0.9 mg
crab, cooked, 3 ounces: 0.8 mgAbout 40–45% of iron in animal tissue and func-
tionally all the iron in plants is nonheme iron. Non-
heme iron is also the type of iron found indietary
supplementsand added to iron-fortified foods. Non-
heme iron is less easily used by humans; it must be
changed in the digestive system before it can be
absorbed. Only about 2–10% of nonheme iron in
food is absorbed compared to 20–25% of heme iron.
In addition, the absorption of nonheme iron is
strongly influenced by other substances present in
the digestive system. The ability of the body to absorb
nonheme iron is decreased by the simultaneous pres-
ence of tea, coffee, dairy products, phytic acid (a sub-
stance found in grains, dried beans and rice), eggs,soy
protein, and some chocolates. Absorption of nonhemeiron is increased by the simultaneous presence ofvita-
min C, certain organic acids, and a small amount of
meat, fish, or poultry, which boosts the absorption of
nonheme iron as well as providing heme iron. Vegeta-
rians and vegans should take into consideration the
influence of other foods on iron absorption when
planning meals.
The following list gives the approximate iron con-
tent for some common foods that contain nonheme
iron:
cereal, 100% iron fortified, 1 cup: 18 mg
soybeans, boiled, 1 cup: 8.8 mg
tofu, firm, 1/2 cup: 6.22 mg
kidney beans, cooked, 1 cup: 5.2 mg
lima beans, cooked, 1 cup: 4.5
pinto beans, cooked, 1 cup: 3.6 mg
blackstrap molasses, 1 tablespoon: 3.5 mg
raisins, small box, 1.5 ounces: .89 mg
potato, medium with skin: 2.75 mg
cashew nuts, 1 ounce: 1.70 mg
whole wheat bread, 1 slice: 0.9 mgNormal iron requirements
The United States Institute of Medicine (IOM) of
the National Academy of Sciences has developed val-
ues calledDietary Reference Intakes(DRIs) forvita-
minsandminerals. The DRIs consist of three sets of
numbers. The Recommended Dietary Allowance
(RDA) defines the average daily amount of the
nutrient needed to meet the health needs of 97–98%
of the population. The Adequate Intake (AI) is an
estimate set when there is not enough information to
determine an RDA. The Tolerable Upper Intake Level
(UL) is the average maximum amount that can be
taken daily without risking negative side effects. The
DRIs are calculated for children, adult men, adult
women, pregnant women, andbreastfeedingwomen.
Iron requirements vary substantially at different
ages. Periods of rapid growth in children increase the
need for iron. Women who menstruate need more iron
because of blood loss during menstruation. Pregnancy
puts high demands on the iron supply in the body
because of increased production of red blood cells to
supply the developing fetus. In 2001, the IOM set
RDAs for iron based on preventing iron deficiency at
each age. Iron passes into breast milk, and infants can
meet their iron needs through breast milk or iron-
fortified formula. RDAs and ULs for iron are meas-
ured in milligrams (mg).KEY TERMS
Cell differentiation—The process by which stem
cells develop into different types of specialized
cells such as skin, heart, muscle, and blood cells.
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.
Mineral—An inorganic substance found in the
earth that is necessary in small quantities for the
body to maintain a health. Examples: zinc, copper,
iron.Iron