Iron (Fe) is an essential nutrient that carries oxygen and forms part
of the oxygen-carrying proteins, hemoglobin in red blood cells and
myoglobin in muscle. It is also a necessary component of various enzymes.
Body iron is concentrated in the storage forms, ferritin and hemosiderin,
in bone marrow, liver, and spleen. Body iron stores can usually be
estimated from the amount of ferritin protein in serum. Transferrin
protein in the blood transports and delivers iron to cells.
Deficiencies: Severe iron deficiency results in anemia
with small, pale, red blood cells that have a low hemoglobin
concentration. Iron deficiency anemia in pregnancy increases the risk of
premature and low birth weight babies. In young children, iron deficiency
is associated with behavioral abnormalities (such as reduced attention
span), and reduced cognitive performance that may not be fully reversible
by iron replacement. In adults, severe iron deficiency anemia impairs
physical work capacity. In the US, iron deficiency anemia is relatively
rare, but affects 5% of women 20 - 49 years old. Moderate iron deficiency
without anemia is most common in 1 - 2 year-old children (9%), and females
12 - 49 years old (9 - 11%), reflecting rapid growth or menstrual iron
loss, and is less common in other groups.
Dietary recommendations: The 1989 Recommended Dietary
Allowance (RDA) for iron is 6 mg for infants through 6 months of age; 10
mg for older infants and children through 10 years old, men 18 years and
older, and women over 50 years; 12 mg for 11-18 year-old males; 15 mg for
11-50 year-old females, including nursing mothers; and 30 mg (a
recommendation which requires supplementation) during pregnancy. The 1989
- 91 USDA Food Consumption Survey indicates that average diets meet or
exceed the RDA for all groups except 1-2 year-old children (91% of RDA)
and women ages 12-49 years (75-80 % of RDA). Iron supplements are not
needed by most people and, because of potential adverse effects of
excessive iron, should not be taken by adult men or postmenopausal women
without demonstrable need.
Food sources: In the US, grain products are a
principal source of dietary iron, followed by meat, poultry and fish, then
vegetables, then legumes, nuts, and soy. Red meat is a rich source of iron
that is well absorbed. Heme iron (about 40% of the iron in meat, poultry,
or fish, and 7-12% of the iron in US diets) is 15-45% absorbed, depending
on iron stores (persons with low iron stores compensate by absorbing more
iron). Nonheme iron, the remaining majority of dietary iron, is 1-15%
absorbed, depending on iron stores and on absorption enhancers (e.g.,
ascorbic acid, an unidentified factor in meat, poultry and fish) or
inhibitors (e.g., phytic acid in whole grains and legumes, polyphenols in
tea, coffee, or red wine, calcium in dairy products or supplements) eaten
concurrently. In the US refined grain products are enriched routinely with
iron. Iron-fortified formula or cereals are useful in preventing iron
deficiency in infants.
Toxicity: Iron supplements intended for other
household members are the most common cause of pediatric poisoning deaths
in the US. In populations of European origin, approximately 1 in 300
people have hemochromatosis, a genetic abnormality of excessive iron
stores. Ten percent of these populations carry a gene (are heterozygous)
for hemochromatosis. Researchers are testing hypotheses that high iron
stores may increase the risk of chronic diseases, such as cancer and heart
disease, through oxidative mechanisms.
