Iron is an essential mineral in human health, playing a role in immune function, cardiovascular health and cognitive development. Its importance was first recognized about 1500 BC, and by the 16th century a relationship between iron and blood was well-known.
Iron is a critical component of:
- hemoglobin (oxygen-transport metalloprotein in red blood cells)
- myoglobin (oxygen-binding protein in muscle tissue)
- ferritin (a protein acting as an iron buffer to stabilize the body’s iron usage)
- a number of important internal enzymes.
Hemoglobin accounts for nearly two-thirds of the iron found in your body, carrying essential oxygen to tissues and organs. About one-sixth of your body's iron is stored in ferritin for use when dietary intake is not sufficient. The remainder of the iron in your body is found in protein tissues that help your body function. Adult men and post-menopausal women lose very little iron except through bleeding. Women with heavy menstrual cycles can lose a significant amount of iron.
There are two forms of dietary iron
Iron is available for supplementation in two forms; heme and nonheme. Heme iron is found in meat, fish, and poultry. Heme iron is absorbed very efficiently by your body. Nonheme iron can be found in vegetables (spinach, corn) and beans (soybeans, kidney beans), but its bioavailability is poor. Although iron in meat is much more bioavailable, it may not be included in certain diets and is in scarce supply in many places around the world.
These factors, combined with physiological reasons, account for the suffering of over 1.3 billion people from iron deficiency anemia, according to the World Health Organization. As a result, iron supplements have been widely used in an attempt to raise ferritin levels to correct this deficiency. Inorganic iron supplements such as ferrous sulfate still have low bioavailability and typically produce undesirable side effects such as gastric upset and nausea.
Note: Iron supplements can be prescribed by a doctor (pharmacological) for a medical reason or can also be a dietary supplement, which can be purchased in health food stores or supermarkets. These two categories should not be confused.
Side effects of therapy with iron are most often diarrhea or constipation and abdominal discomfort. Taken after a meal, side effects decrease but there is an increased risk of interaction with other substances in the stomach. The patient may notice that his/her stools become black. This is completely harmless, but patients must be warned about this to avoid unnecessary concern.
Inorganic iron supplements such as iron sulfates still have low bioavailability and typically do have a higher incidence of adverse events than the organic iron supplement Ferrochel®.
What affects iron absorption?
Iron absorption is greatly influenced by the amount of iron stored in your body. Iron absorption significantly increases when body stores are low. When iron stores are high, absorption decreases to help protect against iron overload. Iron absorption is also influenced by the type of iron in your diet.
Absorption of heme iron is very efficient and not significantly affected by the composition of your diet. Only 1% to 7% of the nonheme iron in vegetable staples such as rice, corn, black beans, soybeans and wheat is absorbed when consumed as a single food. Meat proteins and vitamin C will improve the absorption of nonheme iron.
Calcium, polyphenols and tannins found in tea, and phytates, which are a component of plant foods such as legumes, rice and grains, can decrease the absorption of nonheme iron. Some proteins found in soybeans also inhibit nonheme iron absorption. Most healthy individuals can maintain normal iron stores when the diet provides a wide variety of foods.
The RDA for Iron
The Recommended Dietary Allowance (RDA) is the daily dietary intake level that is sufficient to meet the nutrient requirements of most all healthy individuals in each life-stage and gender group.
9 to 13 years: 8 mg
14-18 years: 15 mg
19-50 years: 18 mg
51+ years: 8 mg
9 to 13 years: 8 mg
14-18 years: 11 mg
19-50 years: 8 mg
51+ years: 8 mg
Infants and Children
7 to 12 months: 11 mg
1 to 3 years: 7 mg
4 to 8 years: 10 mg
For more detailed information on iron, visit the Department of Health and Human Services Center for Disease Control (CDC) or download Chapter 9 (Iron) of Dietary Reference Intakes for Vitamin A,
Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese,
Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001) published by the National Academy
of Sciences. Institute of Medicine. Food and Nutrition Board.