Wacky Wednesday: The Iron Fact Sheet

Information gathered from: Office of Dietary Supplements.

Iron: What is it?

Iron, one of the most abundant metals on Earth, is essential to most life forms and to normal human physiology. Iron is an integral part of many proteins and enzymes that maintain good health. In humans, iron is an essential component of proteins involved in oxygen transport . It is also essential for the regulation of cell growth and differentiation . A deficiency of iron limits oxygen delivery to cells, resulting in fatigue, poor work performance, and decreased immunity . On the other hand, excess amounts of iron can result in toxicity and even death.

Almost two-thirds of iron in the body is found in hemoglobin, the protein in red blood cells that carries oxygen to tissues. Smaller amounts of iron are found in myoglobin, a protein that helps supply oxygen to muscle, and in enzymes that assist biochemical reactions. Iron is also found in proteins that store iron for future needs and that transport iron in blood. Iron stores are regulated by intestinal iron absorption.

What affects iron absorption?

Iron absorption refers to the amount of dietary iron that the body obtains and uses from food. Healthy adults absorb about 10% to 15% of dietary iron, but individual absorption is influenced by several factors.

Storage levels of iron have the greatest influence on iron absorption. Iron absorption increases when body stores are low. When iron stores are high, absorption decreases to help protect against toxic effects of iron  overload.

What is the recommended intake for iron?

Recommendations for iron are provided in the Dietary Reference Intakes (DRIs) developed by the Institute of Medicine of the National Academy of Sciences  Dietary Reference Intakes is the general term for a set of reference values used for planning and assessing nutrient intake for healthy people.

Table 3: Recommended Dietary Allowances for Iron for Infants (7 to 12 months), Children, and Adults [1]
Age Males
(mg/day)
Females
(mg/day)
Pregnancy
(mg/day)
Lactation
(mg/day)

7 to 12 months

11

11

N/A

N/A

1 to 3 years

7

7

N/A

N/A

4 to 8 years

10

10

N/A

N/A

9 to 13 years

8

8

N/A

N/A

14 to 18 years

11

15

27

10

19 to 50 years

8

18

27

9

51+ years

8

8

N/A

N/A

Healthy full term infants are born with a supply of iron that lasts for 4 to 6 months. There is not enough evidence available to establish a RDA for iron for infants from birth through 6 months of age.

Chronic malabsorption can contribute to iron depletion and deficiency by limiting dietary iron absorption or by contributing to intestinal blood loss. Most iron is absorbed in the small intestines. Gastrointestinal disorders that result in inflammation of the small intestine may result in diarrhea, poor absorption of dietary iron, and iron depletion.

Signs of iron deficiency anemia include:

  • feeling tired and weak
  • decreased work and school performance
  • slow cognitive and social development during childhood
  • difficulty maintaining body temperature
  • decreased immune function, which increases susceptibility to infection
  • glossitis (an inflamed tongue)
Table 1: Selected Food Sources of Heme Iron [10]
Food Milligrams
per serving
% DV*

Chicken liver, pan-fried, 3 ounces

11.0

61

Oysters, canned, 3 ounces

5.7

32

Beef liver, pan-fried, 3 ounces

5.2

29

Beef, chuck, blade roast, lean only, braised, 3 ounces

3.1

17

Turkey, dark meat, roasted, 3 ounces

2.0

11

Beef, ground, 85% lean, patty, broiled, 3 ounces

2.2

12

Beef, top sirloin, steak, lean only, broiled, 3 ounces

1.6

9

Tuna, light, canned in water, 3 ounces

1.3

7

Turkey, light meat, roasted, 3 ounces

1.1

6

Chicken, dark meat, meat only, roasted, 3 ounces

1.1

6

Chicken, light meat, meat only, roasted, 3 ounces

0.9

5

Tuna, fresh, yellowfin, cooked, dry heat, 3 ounces

0.8

4

Crab, Alaskan king, cooked, moist heat, 3 ounces

0.7

4

Pork, loin chop, broiled, 3 ounces

0.7

4

Shrimp, mixed species, cooked, moist heat, 4 large

0.3

2

Halibut, cooked, dry heat, 3 ounces

0.2

1

Table 2: Selected Food Sources of Nonheme Iron [10]
Food Milligrams
per serving
% DV*

Ready-to-eat cereal, 100% iron fortified, ¾ cup

18.0

100

Oatmeal, instant, fortified, prepared with water, 1 packet

11.0

61

Soybeans, mature, boiled, 1 cup

8.8

48

Lentils, boiled, 1 cup

6.6

37

Beans, kidney, mature, boiled, 1 cup

5.2

29

Beans, lima, large, mature, boiled, 1 cup

4.5

25

Ready-to-eat cereal, 25% iron fortified, ¾ cup

4.5

25

Blackeye peas, (cowpeas), mature, boiled, 1 cup

4.3

24

Beans, navy, mature, boiled, 1 cup

4.3

24

Beans, black, mature, boiled, 1 cup

3.6

20

Beans, pinto, mature, boiled, 1 cup

3.6

21

Tofu, raw, firm, ½ cup

3.4

19

Spinach, fresh, boiled, drained, ½ cup

3.2

18

Spinach, canned, drained solids ½ cup

2.5

14

Spinach, frozen, chopped or leaf, boiled ½ cup

1.9

11

Raisins, seedless, packed, ½ cup

1.6

9

Grits, white, enriched, quick, prepared with water, 1 cup

1.5

8

Molasses, 1 tablespoon

0.9

5

Bread, white, commercially prepared, 1 slice

0.9

5

Bread, whole-wheat, commercially prepared, 1 slice

0.7

4

If you follow a vegetarian or vegan lifestyle you may want to consider keeping foods like this in your daily rotation

Iron in the Vegan Diet

by Reed Mangels, PhD, RD
From Simply Vegan 5th Edition

Dried beans and dark green leafy vegetables are especially good sources of iron, even better on a per calorie basis than meat. Iron absorption is increased markedly by eating foods containing vitamin C along with foods containing iron. Vegetarians do not have a higher incidence of iron deficiency than do meat eaters.

Iron is an essential nutrient because it is a central part of hemoglobin, which carries oxygen in the blood. Iron deficiency anemia is a worldwide health problem that is especially common in young women and in children.

Iron is found in food in two forms, heme and non-heme iron. Heme iron, which makes up 40 percent of the iron in meat, poultry, and fish, is well absorbed. Non-heme iron, 60 percent of the iron in animal tissue and all the iron in plants (fruits, vegetables, grains, nuts) is less well absorbed. Because vegan diets only contain non-heme iron, vegans should be especially aware of foods that are high in iron and techniques that can promote iron absorption. Recommendations for iron for vegetarians (including vegans) may be as much as 1.8 times higher than for non-vegetarians .

Some might expect that since the vegan diet contains a form of iron that is not that well absorbed, vegans might be prone to developing iron deficiency anemia. However, surveys of vegans have found that iron deficiency anemia is no more common among vegetarians than among the general population although vegans tend to have lower iron stores.

The reason for the satisfactory iron status of many vegans may be that commonly eaten foods are high in iron, as Table 1 shows. In fact, if the amount of iron in these foods is expressed as milligrams of iron per 100 calories, many foods eaten by vegans are superior to animal-derived foods. This concept is illustrated in Table 2. For example, you would have to eat more than 1700 calories of sirloin steak to get the same amount of iron as found in 100 calories of spinach.

Another reason for the satisfactory iron status of vegans is that vegan diets are high in vitamin C. Vitamin C acts to markedly increase absorption of non-heme iron. Adding a vitamin C source to a meal increases non-heme iron absorption up to six-fold which makes the absorption of non-heme iron as good or better than that of heme iron .

Fortunately, many vegetables, such as broccoli and bok choy, which are high in iron, are also high in vitamin C so that the iron in these foods is very well absorbed. Commonly eaten combinations, such as beans and tomato sauce or stir-fried tofu and broccoli, also result in generous levels of iron absorption.

It is easy to obtain iron on a vegan diet. Table 3 shows several menus whose iron content is markedly higher than the RDA for iron.

Both calcium and tannins (found in tea and coffee) reduce iron absorption. Tea, coffee, and calcium supplements should be used several hours before a meal that is high in iron.

Table 1: Iron Content of Selected Vegan Foods
Food Amount Iron (mg)
Soybeans,cooked 1 cup 8.8
Blackstrap molasses 2 Tbsp 7.2
Lentils, cooked 1 cup 6.6
Spinach, cooked 1 cup 6.4
Tofu 4 ounces 6.4
Bagel, enriched 1 medium 6.4
Chickpeas, cooked 1 cup 4.7
Tempeh 1 cup 4.5
Lima beans, cooked 1 cup 4.5
Black-eyed peas, cooked 1 cup 4.3
Swiss chard, cooked 1 cup 4.0
Kidney beans, cooked 1 cup 3.9
Black beans, cooked 1 cup 3.6
Pinto beans, cooked 1 cup 3.6
Turnip greens, cooked 1 cup 3.2
Potato 1 large 3.2
Prune juice 8 ounces 3.0
Quinoa, cooked 1 cup 2.8
Beet greens, cooked 1 cup 2.7
Tahini 2 Tbsp 2.7
Veggie hot dog, iron-fortified 1 hot dog 2.7
Peas, cooked 1 cup 2.5
Cashews 1/4 cup 2.1
Bok choy, cooked 1 cup 1.8
Bulgur, cooked 1 cup 1.7
Raisins 1/2 cup 1.6
Apricots, dried 15 halves 1.4
Veggie burger, commercial 1 patty 1.4
Watermelon 1/8 medium 1.4
Almonds 1/4 cup 1.3
Kale, cooked 1 cup 1.2
Sunflower seeds 1/4 cup 1.2
Broccoli, cooked 1 cup 1.1
Millet, cooked 1 cup 1.1
Soy yogurt 6 ounces 1.1
Tomato juice 8 ounces 1.0
Sesame seeds 2 Tbsp 1.0
Brussels sprouts, cooked 1 cup 0.9
Sources:USDA Nutrient Database for Standard Reference, Release 24, 2011 and Manufacturer´s information.The RDA for iron is 8 mg/day for adult men and for post-menopausal women and 18 mg/day for pre-menopausal women. Vegetarians (including vegans) may need up to 1.8 times more iron.
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