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. About 15 percent of
your body’s iron is stored for future needs and mobilized when dietary
intake is inadequate. The remainder is in your body’s tissues as part of
proteins that help your body function. Adult men and post-menopausal women
lose very little iron except through bleeding. Women with heavy monthly
periods can lose a significant amount of iron. Your body usually maintains
normal iron status by controlling the amount of iron absorbed from
food
IMPORTANCE: Its major function is to combine with
protein and copper in making hemoglobin. Hemoglobin transports oxygen in
the blood from the lungs to the tissues which need oxygen to maintain
basic life functions. Iron builds up the quality of the blood and
increases resistance to stress and disease. It is also necessary for the
formation of myoglobin which is found only in muscle tissue. Myoglobin
supplies oxygen to muscle cells for use in the chemical reaction that
results in muscle contraction. Iron also prevent fatigue and promotes good
skin tone.
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. Also
may result in weakness, paleness of skin, constipation, anemia.
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. |