Iron
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Iron

Image for iron Iron is a mineral that is found in every living cell. Iron exists in two forms—heme and nonheme. Heme iron is part of the hemoglobin and myoglobin molecules in animal tissues. About 40% of the iron in meat is in the heme form. Nonheme iron comes from animal tissues other than hemoglobin and myoglobin and from plant tissues. It is found in meats, eggs, milk, vegetables, grains, and other plant foods. The body absorbs heme iron much more efficiently than nonheme iron. Much of the iron in our diet comes from foods, such as breads and cereals that are fortified with this mineral. Worldwide, iron deficiency anemia is the most common form of malnutrition.

Functions

Iron's functions include:

  • In hemoglobin, carrying oxygen to cells throughout the body
  • In myoglobin, holding oxygen within the cells, especially heart and skeletal muscle cells
  • Forming collagen, which is the major protein that makes up connective tissue, cartilage, and bone
  • Helping fight infection by synthesizing certain enzymes needed for immune function
  • Helping convert beta carotene to vitamin A
  • Helping make amino acids, which are the building blocks of protein
  • Aiding drug detoxification pathways in the liver
  • Forming part of an enzyme that is essential for the production of several neurotransmitters
  • Synthesizing cellular components that are important to metabolism

Recommended Intake

Iron needs are greatest during times of rapid growth—childhood, adolescence, and pregnancy. Also, women have higher requirements than men, to replace the iron that is lost with monthly menstruation.

Age Group Recommended Dietary Allowance (RDA)
(mg/day)
MaleFemale
0-6 months No RDA;
Adequate Intake (AI) = 0.27
No RDA;
Adequate Intake (AI) = 0.27
7-12 months1111
1-3 years77
4-8 years1010
9-13 years88
14-18 years1115
19-50 years818
51+ years88
Pregnancyn/a27
Lactation, equal to or less than 18 yearsn/a10
Lactation, 19-50 yearsn/a9

Iron Deficiency

Groups of people who are susceptible to being iron deficient are:

  • Women of childbearing years
  • Women runners
  • Infants (depending on their diet)
  • Children
  • The elderly
  • Low-income groups
  • Minorities
  • Crohn’s disease or celiac disease patients. Iron is absorbed from a small intestine, and diseases affecting it may lead to poor absorption from food sources.

Iron-Deficiency Anemia

There are no symptoms of iron deficiency unless you become anemic. If not corrected, iron deficiency can progress to anemia. Symptoms of anemia include:

  • Fatigue: feeling tired all the time or getting tired easily with activities you used to be able to do without difficulty
  • Shortness of breath
  • Lightheadedness or dizziness, especially as you stand up
  • Heart palpitations: a pounding or racing heart when you exert yourself or even at rest
  • Very pale skin, especially the pink lining to your lower eyelids, under your fingernails, or your gums
  • Unusual cravings for substances like ice, dirt, etc. (called pica)

Iron-deficiency anemia is usually treated by increasing iron intake through dietary sources and iron supplementation.

Iron Toxicity

At high levels, iron is toxic. And since the body has no effective means of excreting excess iron, it is possible, although not very common, for iron to accumulate. Iron pills and supplements containing iron that are designed for adults can cause poisoning in children.

Other effects of too much iron include:

  • Damage to the liver and other tissues
  • Reduced ability to use other trace minerals (zinc, iodine, and selenium)

Major Food Sources

Food Sources of Mostly Heme Iron and Some Nonheme Iron

FoodServing size Iron content
(mg)
Oysters, pacific, cooked by moist heat3 ounces7.8
Oysters, eastern, canned3 ounces5.7
Beef liver, braised3 ounces5.8
Lean sirloin, broiled3 ounces2.9
Extra-lean ground beef, broiled3 ounces1.8
Tuna, canned in water, light, drained3 ounces1.3
Skinless chicken, roasted dark meat3 ounces1.1
Skinless chicken, roasted white meat3 ounces1.0
Pork, lean, roasted3 ounces1.0
Salmon, canned with bone3 ounces0.7

Food Sources of Nonheme Iron

FoodServing size Iron content
(mg)
Fortified breakfast cereal1 cup 4.5-18
(check Nutrition Facts label)
Pumpkin seeds1 ounce4.3
Bran1/2 cup3.5
Blackstrap molasses1 tablespoon3.5
Soybean nuts1/2 cup4.0
Spinach, boiled1/2 cup3.2
Red kidney beans, cooked1/2 cup2.6
Lima beans, cooked1/2 cup2.5
Cashews, dry roasted1 ounce1.7
Enriched rice, cooked1/2 cup1.2
Acorn squash, baked1/2 cup cubes1.0
Whole-wheat bread1 slice0.9
Egg yolk1 large yolk0.7
Raisins, seedless1/3 cup1.1
Prunes, dried5 prunes1.1
Peanut butter, chunky2 tablespoons0.6
Apricots, dried3 apricots0.6
White bread, made with enriched flour1 slice0.7
Cod, broiled3 ounces0.4

Other Health Implications Related to Iron

Hemochromatosis

People with the genetic disease hemochromatosis absorb excessive amounts of iron. This leads to a buildup of iron in the bloodstream and in certain organs, including the liver, muscles, pancreas, and heart. Signs and symptoms of disease usually do not appear until midlife. People of Northern European descent and men are at higher risk. Without treatment, high levels of iron can damage these organs. Treatment involves eating a diet low in iron and donating blood regularly.

Heart Disease and Cancer

Some research has suggested that excess levels of iron in the body may lead to an increased risk for heart disease or cancer. These effects may be due to how the body metabolizes iron, as opposed to how much iron is in the diet. However, the research in these areas is still inconclusive.

Tips for Increasing Your Iron Intake

The amount of iron your body absorbs varies depending on several factors. For example, your body will absorb more iron from foods when your iron stores are low and will absorb less when stores are sufficient.

In addition, certain dietary factors affect absorption:

  • Heme iron is absorbed more efficiently than nonheme iron
  • Heme iron enhances the absorption of nonheme iron
  • Vitamin C enhances the absorption of nonheme iron
  • Some substances decrease the absorption of nonheme iron:
    • Oxalic acid, found in spinach and chocolate (However, oxalic acid is broken down with cooking.)
    • Phytic acid, found in wheat bran and beans (legumes)
    • Tannins, found in tea
    • Polyphenols, found in coffee

    Note: Consuming heme iron and/or vitamin C with nonheme can help compensate for these decreases.

To increase your intake and absorption of dietary iron, try the following:

  • Combine heme and nonheme sources of iron.
  • Eat foods rich in vitamin C with nonheme iron sources. Good sources of vitamin C include:
    • Bell peppers
    • Papayas
    • Oranges and orange juice
    • Broccoli
    • Strawberries
    • Grapefruit
    • Cantaloupe
    • Tomatoes and tomato juice
    • Potatoes
    • Cabbage
    • Spinach and collard greens
  • If you drink coffee or tea, do so between meals rather than with a meal.
  • Cook acidic foods in cast iron pots. This can increase iron content up to 30 times.

For infants, breastfeeding should be encouraged until at least 4-6 months, then fortified formulas should be given for at least a year—no cow's milk, soy milk, or goat's milk. Routine supplementation of iron is recommended for infants less than one year, unless they are getting adequate iron through their diet. In general, routine supplementation is not recommended after this point, except to treat anemia or during pregnancy.

RESOURCES:

American Dietetic Association
http://www.eatright.org

Vegetarian Resource Group
http://www.vrg.org/

CANADIAN RESOURCES:

Canadian Council on Food and Nutrition
www.ccfn.ca

Dietitians of Canada
http://www.dietitians.ca/

References:

Centers for Disease Control and Prevention. Recommendations to prevent and control iron deficiency in the United States. Morbidity and Mortality Weekly Report. 1998;47:1-32. Available at: http://wonder.cdc.gov/wonder/PrevGuid/m0051880/m0051880.asp.

Duyff R. The American Dietetic Association's Complete Nutrition Guide . Chronimed Publishing; 1998.

Pennington J. Bowes & Church's Food Values of Portions Commonly Used . 17th ed. Lippincott Williams & Wilkins; 1998.

Wardlaw G, Insel P. Perspectives in Nutrition . 2nd ed. Mosby Year Book, Inc.; 1993.

Moy RJ. Prevalence, consequences and prevention of childhood nutritional iron deficiency: a child public health perspective. Clin Lab Haematol. Oct 2006;28(5)(review):291-8.

Iron Disorders Institute website. Available at: http://www.irondisorders.org/. Last accessed on November 19, 2006.



Last reviewed June 2008 by Dianne Scheinberg MS, RD, LDN

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.


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