IRON

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.

For further information:

Yip, R., Parvanta, I., Cogswell, M. E., Bowman, B. A., Grummer-Strawn, L. M. & Trowbridge, F. R. (1998) Recommendations to Prevent and Control Iron Deficiency in the United States. No. RR-3. US Dept. Health and Human Services, Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report. No. 47: April 3.

Prepared By:

Janet Hunt, Ph.D.
Research Nutritionist
USDA-ARS Human Nutrition Research Ctr
P.O. Box 9034
University Station
Grand Forks, ND 58202-9034
Phone: 701-795-8328
FAX: 701-795-8395
Email: jhunt@gfhnrc.ars.usda.gov