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| Iron
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Iron, one of the most abundant metals on Earth, is essential to most
life forms and to normal human physiology. Iron is an integral part of
many proteins and enzymes that maintain good health. In humans, iron is
an essential component of proteins involved in oxygen transport. It is
also essential for the regulation of cell growth and differentiation.
A deficiency of iron limits oxygen delivery to cells, resulting in fatigue,
poor work performance, and decreased immunity. On the other hand, excess
amounts of iron can result in toxicity and even death.
Almost two-thirds of iron in the body is found in hemoglobin,
the protein in red blood cells that carries oxygen to tissues.
Smaller amounts of iron are found in myoglobin, a protein that
helps supply oxygen to muscle, and in enzymes that assist biochemical
reactions. Iron is also found in proteins that store iron for
future needs and that transport iron in blood. Iron stores are
regulated by intestinal iron absorption.
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There are two forms of dietary iron: heme and nonheme. Heme
iron is derived from hemoglobin, the protein in red blood cells
that delivers oxygen to cells. Heme iron is found in animal foods
that originally contained hemoglobin, such as red meats, fish,
and poultry. Iron in plant foods such as lentils and beans is
arranged in a chemical structure called nonheme iron. This
is the form of iron added to iron-enriched and iron-fortified
foods. Heme iron is absorbed better than nonheme iron, but most
dietary iron is nonheme iron. A variety
of heme and nonheme sources of iron are listed in Tables 1 and
2.
Table 1: Selected Food Sources of Heme Iron
| Food |
Milligrams
per serving |
% DV* |
| Chicken liver, cooked, 3½ ounces |
12.8 |
70 |
| Oysters, breaded and fried, 6 pieces |
4.5 |
25 |
| Beef, chuck, lean only, braised, 3 ounces |
3.2 |
20 |
| Clams, breaded, fried, ¾ cup |
3.0 |
15 |
| Beef, tenderloin, roasted, 3 ounces |
3.0 |
15 |
| Turkey, dark meat, roasted, 3½ ounces |
2.3 |
10 |
| Beef, eye of round, roasted, 3 ounces |
2.2 |
10 |
| Turkey, light meat, roasted, 3½ ounces |
1.6 |
8 |
| Chicken, leg, meat only, roasted, 3½ ounces |
1.3 |
6 |
| Tuna, fresh bluefin, cooked, dry heat, 3 ounces |
1.1 |
6 |
| Chicken, breast, roasted, 3 ounces |
1.1 |
6 |
| Halibut, cooked, dry heat, 3 ounces |
0.9 |
6 |
| Crab, blue crab, cooked, moist heat, 3 ounces |
0.8 |
4 |
| Pork, loin, broiled, 3 ounces |
0.8 |
4 |
| Tuna, white, canned in water, 3 ounces |
0.8 |
4 |
| Shrimp, mixed species, cooked, moist heat, 4 large |
0.7 |
4 |
Table 2: Selected Food Sources of Nonheme Iron
| Food |
Milligrams
per serving |
% DV* |
| Ready-to-eat cereal, 100% iron fortified, ¾ cup |
18.0 |
100 |
| Oatmeal, instant, fortified, prepared with water, 1
cup |
10.0 |
60 |
| Soybeans, mature, boiled, 1 cup |
8.8 |
50 |
| Lentils, boiled, 1 cup |
6.6 |
35 |
| Beans, kidney, mature, boiled, 1 cup |
5.2 |
25 |
| Beans, lima, large, mature, boiled, 1 cup |
4.5 |
25 |
| Beans, navy, mature, boiled, 1 cup |
4.5 |
25 |
| Ready-to-eat cereal, 25% iron fortified, ¾ cup |
4.5 |
25 |
| Beans, black, mature, boiled, 1 cup |
3.6 |
20 |
| Beans, pinto, mature, boiled, 1 cup |
3.6 |
20 |
| Molasses, blackstrap, 1 tablespoon |
3.5 |
20 |
| Tofu, raw, firm, ½ cup |
3.4 |
20 |
| Spinach, boiled, drained, ½ cup |
3.2 |
20 |
| Spinach, canned, drained solids ½ cup |
2.5 |
10 |
| Black-eyed peas (cowpeas), boiled, 1 cup |
1.8 |
10 |
| Spinach, frozen, chopped, boiled ½ cup |
1.9 |
10 |
| Grits, white, enriched, quick, prepared with water,
1 cup |
1.5 |
8 |
| Raisins, seedless, packed, ½ cup |
1.5 |
8 |
| Whole wheat bread, 1 slice |
0.9 |
6 |
| White bread, enriched, 1 slice |
0.9 |
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 FDA requires all food labels to
include the percent DV (%DV) for iron. The percent DV tells you what percent
of the DV is provided in one serving. The DV for iron is 18 milligrams (mg).
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.
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Iron absorption refers to the amount of dietary iron that
the body obtains and uses from food. Healthy adults absorb about
10% to 15% of dietary iron, but individual absorption is influenced
by several factors .
Storage levels of iron have the greatest influence on iron absorption.
Iron absorption increases when body stores are low. When iron
stores are high, absorption decreases to help protect against
toxic effects of iron overload. Iron
absorption is also influenced by the type of dietary iron consumed.
Absorption of heme iron from meat proteins is efficient. Absorption
of heme iron ranges from 15% to 35%, and is not significantly
affected by diet. In
contrast, 2% to 20% of nonheme iron in plant foods such as rice,
maize, black beans, soybeans and wheat is absorbed. Nonheme
iron absorption is significantly influenced by various food components
.
Meat proteins and vitamin C will improve the absorption of nonheme
iron.
Tannins (found in tea), calcium, polyphenols, and phytates (found
in legumes and whole grains) can decrease absorption of nonheme
iron.
Some proteins found in soybeans also inhibit nonheme iron absorption. It
is most important to include foods that enhance nonheme iron absorption
when daily iron intake is less than recommended, when iron losses
are high (which may occur with heavy menstrual losses), when iron
requirements are high (as in pregnancy), and when only vegetarian
nonheme sources of iron are consumed. Return to top
Recommendations for iron are provided in the Dietary Reference
Intakes (DRIs) developed by the Institute of Medicine of the National
Academy of Sciences. 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. 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. The UL, on the other hand, is the maximum
daily intake unlikely to result in adverse health effects. Table
3 lists the RDAs for iron, in milligrams, for infants, children
and adults.
Table 3: Recommended Dietary Allowances for Iron for Infants
(7 to 12 months), Children, and Adults
| Age |
Males
(mg/day) |
Females
(mg/day) |
Pregnancy
(mg/day) |
Lactation
(mg/day) |
| 7 to 12 months |
11 |
11 |
N/A |
N/A |
| 1 to 3 years |
7 |
7 |
N/A |
N/A |
| 4 to 8 years |
10 |
10 |
N/A |
N/A |
| 9 to 13 years |
8 |
8 |
N/A |
N/A |
| 14 to 18 years |
11 |
15 |
27 |
10 |
| 19 to 50 years |
8 |
18 |
27 |
9 |
| 51+ years |
8 |
8 |
N/A |
N/A |
Healthy full term infants are born with a supply of iron that
lasts for 4 to 6 months. There is not enough evidence available
to establish a RDA for iron for infants from birth through 6 months
of age. Recommended iron intake for this age group is based on
an Adequate Intake (AI) that reflects the average iron intake
of healthy infants fed breast milk. Table
4 lists the AI for iron, in milligrams, for infants up to 6 months
of age.
Table 4: Adequate Intake for Iron for Infants (0 to 6
months)
Age
(months) |
Males and Females
(mg/day) |
| 0 to 6 |
0.27 |
Iron in human breast milk is well absorbed by infants. It is estimated
that infants can use greater than 50% of the iron in breast milk
as compared to less than 12% of the iron in infant formula. The amount
of iron in cow's milk is low, and infants poorly absorb it. Feeding
cow's milk to infants also may result in gastrointestinal bleeding.
For these reasons, cow's milk should not be fed to infants until
they are at least 1 year old. The American
Academy of Pediatrics (AAP) recommends that infants be exclusively
breast fed for the first six months of life. Gradual introduction
of iron-enriched solid foods should complement breast milk from
7 to 12 months of age. Infants
weaned from breast milk before 12 months of age should receive
iron-fortified infant formula. Infant
formulas that contain from 4 to 12 milligrams of iron per liter
are considered iron-fortified.
Data from the National Health and Nutrition Examination Survey
(NHANES) describe dietary intake of Americans 2 months of age
and older. NHANES (1988-94) data suggest that males of all racial
and ethnic groups consume recommended amounts of iron. However,
iron intakes are generally low in females of childbearing age
and young children.
Researchers also examine specific groups within the NHANES population.
For example, researchers have compared dietary intakes of adults
who consider themselves to be food insufficient (and therefore
have limited access to nutritionally adequate foods) to those
who are food sufficient (and have easy access to food). Older
adults from food insufficient families had significantly lower
intakes of iron than older adults who are food sufficient. In
one survey, twenty percent of adults age 20 to 59 and 13.6% of
adults age 60 and older from food insufficient families consumed
less than 50% of the RDA for iron, as compared to 13% of adults
age 20 to 50 and 2.5% of adults age 60 and older from food sufficient
families.
Iron intake is negatively influenced by low nutrient density foods,
which are high in calories but low in vitamins and minerals. Sugar
sweetened sodas and most desserts are examples of low nutrient
density foods, as are snack foods such as potato chips. Among
almost 5,000 children and adolescents between the ages of 8 and
18 who were surveyed, low nutrient density foods contributed almost
30% of daily caloric intake, with sweeteners and desserts jointly
accounting for almost 25% of caloric intake. Those children and
adolescents who consumed fewer "low nutrient density" foods were
more likely to consume recommended amounts of iron.
Data from The Continuing Survey of Food Intakes by Individuals
(CSFII1994-6 and 1998) was used to examine the effect of major
food and beverage sources of added sugars on micronutrient intake
of U.S. children aged 6 to 17 years. Researchers found that consumption
of presweetened cereals, which are fortified with iron, increased
the likelihood of meeting recommendations for iron intake. On
the other hand, as intake of sugar-sweetened beverages, sugars,
sweets, and sweetened grains increased, children were less likely
to consume recommended amounts of iron. Return to top
The World Health Organization considers iron deficiency the
number one nutritional disorder in the world. As
many as 80% of the world's population may be iron deficient, while
30% may have iron deficiency anemia.
Iron deficiency develops gradually and usually begins with a negative
iron balance, when iron intake does not meet the daily need for
dietary iron. This negative balance initially depletes the storage
form of iron while the blood hemoglobin level, a marker of iron
status, remains normal. Iron deficiency anemia is an advanced
stage of iron depletion. It occurs when storage sites of iron
are deficient and blood levels of iron cannot meet daily needs.
Blood hemoglobin levels are below normal with iron deficiency
anemia.
Iron deficiency anemia can be associated with low dietary intake
of iron, inadequate absorption of iron, or excessive blood loss
. Women
of childbearing age, pregnant women, preterm and low birth weight
infants, older infants and toddlers, and teenage girls are at
greatest risk of developing iron deficiency anemia because they
have the greatest need for iron. Women
with heavy menstrual losses can lose a significant amount of iron
and are at considerable risk for iron deficiency. Adult
men and post-menopausal women lose very little iron, and have
a low risk of iron deficiency.
Individuals with kidney failure, especially those being treated
with dialysis, are at high risk for developing iron deficiency
anemia. This is because their kidneys cannot create enough erythropoietin,
a hormone needed to make red blood cells. Both iron and erythropoietin
can be lost during kidney dialysis. Individuals who receive routine
dialysis treatments usually need extra iron and synthetic erythropoietin
to prevent iron deficiency.
Vitamin A helps mobilize iron from its storage sites, so a deficiency
of vitamin A limits the body's ability to use stored iron. This
results in an "apparent" iron deficiency because hemoglobin levels
are low even though the body can maintain normal amounts of stored
iron.
While uncommon in the U.S., this problem is seen in developing
countries where vitamin A deficiency often occurs.
Chronic malabsorption can contribute to iron depletion and deficiency
by limiting dietary iron absorption or by contributing to intestinal
blood loss. Most iron is absorbed in the small intestines. Gastrointestinal
disorders that result in inflammation of the small intestine may
result in diarrhea, poor absorption of dietary iron, and iron
depletion.
Signs of iron deficiency anemia include:
feeling tired and weak
decreased work and school performance
slow cognitive and social development during childhood
difficulty maintaining body temperature
decreased immune function, which increases susceptibility
to infection
glossitis (an inflamed tongue)
Eating nonnutritive substances such as dirt and clay, often
referred to as pica or geophagia, is sometimes seen in persons
with iron deficiency. There is disagreement about the cause
of this association. Some researchers believe that these eating
abnormalities may result in an iron deficiency. Other researchers
believe that iron deficiency may somehow increase the likelihood
of these eating problems.
People with chronic infectious, inflammatory, or malignant disorders
such as arthritis and cancer may become anemic. However, the
anemia that occurs with inflammatory disorders differs from
iron deficiency anemia and may not respond to iron supplements.
Research suggests that inflammation may over-activate a protein
involved in iron metabolism. This protein may inhibit iron absorption
and reduce the amount of iron circulating in blood, resulting
in anemia.
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Three groups of people are most likely to benefit from iron
supplements: people with a greater need for iron, individuals
who tend to lose more iron, and people who do not absorb iron
normally. These individuals include :
pregnant women
preterm and low birth weight infants
older infants and toddlers
teenage girls
women of childbearing age, especially those with heavy menstrual
losses
people with renal failure, especially those undergoing routine
dialysis
people with gastrointestinal disorders who do not absorb iron normally
Celiac Disease and Crohn's Syndrome are associated with gastrointestinal
malabsorption and may impair iron absorption. Iron supplementation may
be needed if these conditions result in iron deficiency anemia.
Women taking oral contraceptives may experience less bleeding during
their periods and have a lower risk of developing an iron deficiency.
Women who use an intrauterine device (IUD) to prevent pregnancy may
experience more bleeding and have a greater risk of developing an iron
deficiency. If laboratory tests indicate iron deficiency anemia, iron
supplements may be recommended.
Total dietary iron intake in vegetarian diets may meet recommended levels;
however that iron is less available for absorption than in diets that
include meat. Vegetarians who exclude all animal products from their
diet may need almost twice as much dietary iron each day as non-vegetarians
because of the lower intestinal absorption of nonheme iron in plant
foods. Vegetarians should consider consuming nonheme iron sources together
with a good source of vitamin C, such as citrus fruits, to improve the
absorption of nonheme iron.
There are many causes of anemia, including iron deficiency. There are
also several potential causes of iron deficiency. After a thorough evaluation,
physicians can diagnose the cause of anemia and prescribe the appropriate
treatment.
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Nutrient requirements increase during pregnancy to support fetal
growth and maternal health. Iron requirements of pregnant women are
approximately double that of non-pregnant women because of increased
blood volume during pregnancy, increased needs of the fetus, and blood
losses that occur during delivery. If iron intake does not meet increased
requirements, iron deficiency anemia can occur. Iron deficiency anemia
of pregnancy is responsible for significant morbidity, such as premature
deliveries and giving birth to infants with low birth weight .
Low levels of hemoglobin and hematocrit may indicate iron deficiency.
Hemoglobin is the protein in red blood cells that carries oxygen to
tissues. Hematocrit is the proportion of whole blood that is made up
of red blood cells. Nutritionists estimate that over half of pregnant
women in the world may have hemoglobin levels consistent with iron deficiency.
In the U.S., the Centers for Disease Control (CDC) estimated that 12%
of all women age 12 to 49 years were iron deficient in 1999-2000. When
broken down by groups, 10% of non-Hispanic white women, 22% of Mexican-American
women, and 19% of non-Hispanic black women were iron deficient. Prevalence
of iron deficiency anemia among lower income pregnant women has remained
the same, at about 30%, since the 1980s.
The RDA for iron for pregnant women increases to 27 mg per day. Unfortunately,
data from the 1988-94 NHANES survey suggested that the median iron intake
among pregnant women was approximately 15 mg per day. When median iron
intake is less than the RDA, more than half of the group consumes less
iron than is recommended each day.
Several major health organizations recommend iron supplementation during
pregnancy to help pregnant women meet their iron requirements. The CDC
recommends routine low-dose iron supplementation (30 mg/day) for all
pregnant women, beginning at the first prenatal visit. When a low hemoglobin
or hematocrit is confirmed by repeat testing, the CDC recommends larger
doses of supplemental iron. The Institute of Medicine of the National
Academy of Sciences also supports iron supplementation during pregnancy.
Obstetricians often monitor the need for iron supplementation during
pregnancy and provide individualized recommendations to pregnant women.
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Iron supplementation is indicated when diet alone cannot restore
deficient iron levels to normal within an acceptable timeframe. Supplements
are especially important when an individual is experiencing clinical
symptoms of iron deficiency anemia. The goals of providing oral iron
supplements are to supply sufficient iron to restore normal storage
levels of iron and to replenish hemoglobin deficits. When hemoglobin
levels are below normal, physicians often measure serum ferritin, the
storage form of iron. A serum ferritin level less than or equal to 15
micrograms per liter confirms iron deficiency anemia in women, and suggests
a possible need for iron supplementation.
Supplemental iron is available in two forms: ferrous and ferric. Ferrous
iron salts (ferrous fumarate, ferrous sulfate, and ferrous gluconate)
are the best absorbed forms of iron supplements. Elemental iron is the
amount of iron in a supplement that is available for absorption. Figure
1 lists the percent elemental iron in these supplements.
Figure 1: Percent Elemental Iron in Iron Supplements
The amount of iron absorbed decreases with increasing doses. For this
reason, it is recommended that most people take their prescribed daily
iron supplement in two or three equally spaced doses. For adults who
are not pregnant, the CDC recommends taking 50 mg to 60 mg of oral elemental
iron (the approximate amount of elemental iron in one 300 mg tablet
of ferrous sulfate) twice daily for three months for the therapeutic
treatment of iron deficiency anemia. However, physicians evaluate each
person individually, and prescribe according to individual needs.
Therapeutic doses of iron supplements, which are prescribed for iron
deficiency anemia, may cause gastrointestinal side effects such as nausea,
vomiting, constipation, diarrhea, dark colored stools, and/or abdominal
distress. Starting with half the recommended dose and gradually increasing
to the full dose will help minimize these side effects. Taking the supplement
in divided doses and with food also may help limit these symptoms. Iron
from enteric coated or delayed-release preparations may have fewer side
effects, but is not as well absorbed and not usually recommended.
Physicians monitor the effectiveness of iron supplements by measuring
laboratory indices, including reticulocyte count (levels of newly formed
red blood cells), hemoglobin levels, and ferritin levels. In the presence
of anemia, reticulocyte counts will begin to rise after a few days of
supplementation. Hemoglobin usually increases within 2 to 3 weeks of
starting iron supplementation.
In rare situations parenteral iron (provided by injection or I.V.) is
required. Doctors will carefully manage the administration of parenteral
iron.
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Iron deficiency is uncommon among adult men and postmenopausal
women. These individuals should only take iron supplements when prescribed
by a physician because of their greater risk of iron overload. Iron
overload is a condition in which excess iron is found in the blood and
stored in organs such as the liver and heart. Iron overload is associated
with several genetic diseases including hemochromatosis, which affects
approximately 1 in 250 individuals of northern European descent. Individuals
with hemochromatosis absorb iron very efficiently, which can result
in a build up of excess iron and can cause organ damage such as cirrhosis
of the liver and heart failure . Hemochromatosis is often not diagnosed
until excess iron stores have damaged an organ. Iron supplementation
may accelerate the effects of hemochromatosis, an important reason why
adult men and postmenopausal women who are not iron deficient should
avoid iron supplements. Individuals with blood disorders that require
frequent blood transfusions are also at risk of iron overload and are
usually advised to avoid iron supplements.
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Iron and heart disease:
Because known risk factors cannot explain all cases of heart disease,
researchers continue to look for new causes. Some evidence suggests
that iron can stimulate the activity of free radicals. Free radicals
are natural by-products of oxygen metabolism that are associated with
chronic diseases, including cardiovascular disease. Free radicals may
inflame and damage coronary arteries, the blood vessels that supply
the heart muscle. This inflammation may contribute to the development
of atherosclerosis, a condition characterized by partial or complete
blockage of one or more coronary arteries. Other researchers suggest
that iron may contribute to the oxidation of LDL ("bad") cholesterol,
changing it to a form that is more damaging to coronary arteries.
As far back as the 1980s, some researchers suggested that the regular
menstrual loss of iron, rather than a protective effect from estrogen,
could better explain the lower incidence of heart disease seen in pre-menopausal
women. After menopause, a woman's risk of developing coronary heart
disease increases along with her iron stores. Researchers have also
observed lower rates of heart disease in populations with lower iron
stores, such as those in developing countries. In those geographic areas,
lower iron stores are attributed to low meat (and iron) intake, high
fiber diets that inhibit iron absorption, and gastrointestinal (GI)
blood (and iron) loss due to parasitic infections.
In the 1980s, researchers linked high iron stores with increased risk
of heart attacks in Finnish men. However, more recent studies have not
supported such an association.
One way of testing an association between iron stores and coronary heart
disease is to compare levels of ferritin, the storage form of iron,
to the degree of atherosclerosis in coronary arteries. In one study,
researchers examined the relationship between ferritin levels and atherosclerosis
in 100 men and women referred for cardiac examination. In this population,
higher ferritin levels were not associated with an increased degree
of atherosclerosis, as measured by angiography. Coronary angiography
is a technique used to estimate the degree of blockage in coronary arteries.
In a different study, researchers found that ferritin levels were higher
in male patients diagnosed with coronary artery disease. They did not
find any association between ferritin levels and risk of coronary disease
in women.
A second way to test this association is to examine rates of coronary
disease in people who frequently donate blood. If excess iron stores
contribute to heart disease, frequent blood donation could potentially
lower heart disease rates because of the iron loss associated with blood
donation. Over 2,000 men over age 39 and women over age 50 who donated
blood between 1988 and 1990 were surveyed 10 years later to compare
rates of cardiac events to frequency of blood donation. Cardiac events
were defined as (1) occurrence of an acute myocardial infarction (heart
attack), (2) undergoing angioplasty, a medical procedure that opens
a blocked coronary artery; or (3) undergoing bypass grafting, a surgical
procedure that replaces blocked coronary arteries with healthy blood
vessels. Researchers found that frequent donors, who donated more than
1 unit of whole blood each year between 1988 and 1990, were less likely
to experience cardiac events than casual donors (those who only donated
a single unit in that 3-year period). Researchers concluded that frequent
and long-term blood donation may decrease the risk of cardiac events.
Conflicting results, and different methods to measure iron stores, make
it difficult to reach a final conclusion on this issue. However, researchers
know that it is feasible to decrease iron stores in healthy individual
through phlebotomy (blood letting or donation). Using phlebotomy, researchers
hope to learn more about iron levels and cardiovascular disease.
Iron and intense exercise:
Many men and women who engage in regular, intense exercise such as jogging,
competitive swimming, and cycling have marginal or inadequate iron status.
Possible explanations include increased gastrointestinal blood loss
after running and a greater turnover of red blood cells. Also, red blood
cells within the foot can rupture while running. For these reasons,
the need for iron may be 30% greater in those who engage in regular
intense exercise.
Three groups of athletes may be at greatest risk of iron depletion and
deficiency: female athletes, distance runners, and vegetarian athletes.
It is particularly important for members of these groups to consume
recommended amounts of iron and to pay attention to dietary factors
that enhance iron absorption. If appropriate nutrition intervention
does not promote normal iron status, iron supplementation may be indicated.
In one study of female swimmers, researchers found that supplementation
with 125 milligrams (mg) of ferrous sulfate per day prevented iron depletion.
These swimmers maintained adequate iron stores, and did not experience
the gastrointestinal side effects often seen with higher doses of iron
supplementation.
Iron and mineral interactions
Some researchers have raised concerns about interactions between iron,
zinc, and calcium. When iron and zinc supplements are given together
in a water solution and without food, greater doses of iron may decrease
zinc absorption. However, the effect of supplemental iron on zinc absorption
does not appear to be significant when supplements are consumed with
food. There is evidence that calcium from supplements and dairy foods
may inhibit iron absorption, but it has been very difficult to distinguish
between the effects of calcium on iron absorption versus other inhibitory
factors such as phytate.
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There is considerable potential for iron toxicity because very
little iron is excreted from the body. Thus, iron can accumulate in
body tissues and organs when normal storage sites are full. For example,
people with hemachromatosis are at risk of developing iron toxicity
because of their high iron stores.
In children, death has occurred from ingesting 200 mg of iron. It
is important to keep iron supplements tightly capped and away from children's
reach. Any time excessive iron intake
is suspected, immediately call your physician or Poison
Control Center, or visit your local emergency room. Doses of iron prescribed
for iron deficiency anemia in adults are associated with constipation,
nausea, vomiting, and diarrhea, especially when the supplements are
taken on an empty stomach.
In 2001, the Institute of Medicine of the National Academy of Sciences
set a tolerable upper intake level (UL) for iron for healthy people.
There may be times when a physician prescribes an intake higher than
the upper limit, such as when individuals with iron deficiency anemia
need higher doses to replenish their iron stores. Table 5 lists the
ULs for healthy adults, children, and infants 7 to 12 months of age.
Table 5: Tolerable Upper Intake Levels for Iron for Infants
7 to 12 months, Children, and Adults
| Age |
Males
(mg/day) |
Females
(mg/day) |
Pregnancy
(mg/day) |
Lactation
(mg/day) |
| 7 to 12 months |
40 |
40 |
N/A |
N/A |
| 1 to 13 years |
40 |
40 |
N/A |
N/A |
| 14 to 18 years |
45 |
45 |
45 |
45 |
| 19 + years |
45 |
45 |
45 |
45 |
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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". Beef
and turkey are good sources of heme iron while beans and lentils are
high in nonheme iron. In addition, many foods, such as ready-to-eat
cereals, are fortified with iron. It is important for anyone who is
considering taking an iron supplement to first consider whether their
needs are being met by natural dietary sources of heme and nonheme iron
and foods fortified with iron, and to discuss their potential need for
iron supplements with their physician.
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