17.1: Iron

Iron is a key part of several important proteins, but hemoglobin has the most iron. One of the many ancient folk sayings about food is, “Pale foods can’t make red blood.” This is generally true. The redness of blood depends on iron, which—like beta-carotene—is a food colorant. Among the best sources of iron are such dark foods as red meats (especially beef liver), dark whole grains, prunes, raisins, molasses, and all the dark green, leafy vegetables.

Because iron is found in many foods, one might not expect iron shortages to be widespread. In fact, it’s the world’s most common nutritional deficiency. Growth, menstruation, and childbearing make a big dent in the body’s supply of iron, making iron deficiency especially common among children and women of childbearing age.

Figure 17-1: Simple lab test for anemia: Spin blood in specially marked hematocrit tube; red blood cells pack at the bottom; read its percentage in blood on the tube markings.

Two-thirds of body iron is found in molecules of hemoglobin, which are packaged into red blood cells, giving them—and blood—their color. Plentiful hemoglobin adds a pinkish hue to skin. Those who have too little hemoglobin (i.e., are anemic) tend to be pale.

The iron in hemoglobin is essential as a carrier of oxygen. Without hemoglobin, the blood of an average adult (about 5 quarts) would carry only about 1 tablespoon of oxygen. Hemoglobin increases the oxygen-carrying capacity of blood by about 70-fold, to about a quart of oxygen.

Hemoglobin picks up oxygen from the lungs, and carries it throughout the body, supplying it to each cell. When oxygenated, the blood is bright red. When the hemoglobin gives up its oxygen to a cell, blood takes on a dark purplish-red color.

Iron-Deficiency Anemia

A person with anemia has fewer red blood cells and/or less hemoglobin in their red blood cells (see Fig. 17-1). This condition can be due to blood loss, impaired production of red blood cells or hemoglobin, or increased destruction of red blood cells. Despite the many possible causes of anemia, the common result is a reduced capacity of the blood to carry oxygen.

Iron deficiency is the most common cause of anemia. Since iron is an essential part of hemoglobin, not enough iron means not enough hemoglobin—and red blood cells that are small and pale (see Fig. 17-2).

Mineral	Function	Source	Deficiency	Possible Toxicity
Chromium	Insulin cofactor	Whole grains, liver, brewer's yeast, nuts, some beers and red wine, mushrooms	Impaired insulin action	None reported, except from occupational inhalation
Copper	Cofactor in making hemoglobin, collagen	Liver, seafood, nuts, seeds, grains, copper plumbing	Rare; anemia, retarded growth, liver damage	Vomiting, diarrhea
Fluoride	Strengthen teeth and bone	Fluoride in drinking water, tea, seafood	Increased tooth decay	Mottling of tooth enamel
Iodine	Part of thyroid hormone	Seafood, iodized salt, diary products	Simple goiter, intellectual disability	Goiter, inhibit making of thyroid hormone
Iron	Part of hemoglobin & other key proteins	Liver, red meat, eggs, fortified cereals, legumes, spinach	Anemia, fatigue, infections	Hemochromatosis vomiting, diarrhea
Manganese	Cofactor in metabolism	Whole grains, nuts, organ meats	Rare; nausea, vomiting	None reported, except from occupational inhalation
Molybdenum	Cofactor in metabolism	Beans, grains, nuts	Rare	Gout-like symptoms
Selenium	Antioxidant	Meat, seafood, milk, grains	Heart muscle disorder	Brittleness and loss of hair and nails
Zinc	Cofactor in metabolism	Meat, milk, wheat, germ, legumes, shellfish	Retarded growth, reduced sense of smell and taste, fewer white blood cells, skin lesions	Nausea, cramps, diarrhea, fever

Table 17-1: Trace Minerals

An anemic person tires easily and often has such symptoms as weakness, dizziness, headache, drowsiness, and irritability. In short, the person has lower physical and mental capacity for work and productivity. Also, anemia can lessen the body’s ability to increase heat production in response to cold (“cold intolerance”). Severe anemia can cause cessation of menstrual periods, loss of sexual desire, heart failure, and shock.

Iron deficiency can be caused by a greater need for iron (as when growing or pregnant), a dietary deficiency of iron, reduced absorption of iron (e.g., reduced stomach acidity from taking excessive amounts of antacids), or a combination of these factors. As said earlier, iron-deficiency anemia is most common among children and women of child-bearing age.

Children and adolescents need more iron for their increasing blood volume and growing bodies. Menstruating women lose iron in menstrual blood. Because women vary in the amount of menstrual blood losses, they vary in the amount of iron that they need for replacement.

It follows that any condition that changes the amount of menstrual blood will also change the iron requirement. Birth-control pills, for example, reduce menstrual blood losses. Menstruation can be scanty or cease entirely with extreme thinness (as sometimes occurs with anorexia nervosa or among ballet dancers) and with extreme exercise (as in competitive runners who train vigorously). Although there are no menstrual blood losses during pregnancy, more iron is needed for the growing fetus and woman’s bigger blood volume.

Figure 17-2: Iron deficiency is the most common cause of anemia.

Iron-deficiency anemia is unusual for men and post-menopausal women, since they have minimal iron losses. An exception to this, of course, would be iron losses due to blood donations. Blood banks check for anemia before taking blood, and don’t allow donations of more than a pint about every 2 months. When iron-deficiency anemia is seen in men and postmenopausal women who are not blood donors, chronic bleeding—especially in the digestive tract (as in a bleeding ulcer)—is suspected and should be investigated.

Iron Deficiency and Lead Absorption

Iron deficiency also has a bearing on lead toxicity, particularly among children. During periods of rapid growth, lead is absorbed readily. Infants and young children absorb 5 to 10 times more lead than adults from a given dose. Furthermore, lead absorption and/or toxicity is increased when there is a deficiency of iron (or calcium or zinc).

Lead exposure has fallen dramatically due to such changes as eliminating lead in gasoline and house paint, banning the use of lead and lead solder in plumbing, and in food cans. The aim is to eliminate lead exposure from all sources—no safe level of lead exposure has been found. Hundreds of thousands of pre-school children in the U.S. have had substantial lead exposure, leading to permanent intellectual and behavioral deficits.²

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Remnants of lead-based paint used before 1978 is still a major source of lead exposure; young children often ingest flakes or dust from the paint that can contaminate the house and the soil around it.

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Lead is a potent poison with widespread effects. It can, for example, damage the kidneys (and cause high blood pressure), red blood cells (and cause anemia), and the reproductive system (and cause infertility). As said earlier, even small amounts of lead can damage the brain (and impair cognition and behavior).

It’s been theorized that severe lead poisoning caused infertility and mental illness in the ruling class of ancient Rome, and that this was a factor in the fall of the Roman Empire. Lead plumbing contaminated their drinking water, and lead utensils and vessels (used for cooking, drinking, and storage) contaminated their food and drink.

Iron in Foods

Those with iron-deficiency anemia need to increase their intake of iron and/or increase their ability to absorb the iron in their diet. Compared to other nutrients, iron is poorly absorbed. This is an important natural safeguard, because excessive iron in the body can be toxic.

Aside from blood losses, very little iron is lost from the body once it’s absorbed. So the intestine serves as the gatekeeper by adjusting iron absorption. Absorption is normally low, but increases when the body needs more iron.

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Milligram (mg) iron in about 3 oz. lean, cooked portions of animal tissues:

• beef liver 7.5 mg
• hamburger 3.9 mg
• lamb 2.6 mg
• skinless dark chicken meat 1.4 mg
• skinless light chicken meat 1.1 mg
• salmon, swordfish, or trout 1.0 mg

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Dietary iron can be categorized into two types. Iron ingested as a part of heme (a complex molecule with an atom of iron in its core) is called heme iron; other forms (“inorganic iron”) are called non-heme iron (see Fig. 17-3).

Heme Iron

Heme iron is found in animal tissue, mainly in hemoglobin and myoglobin (an oxygen-carrying molecule similar to hemoglobin, but found in muscle). About half the iron in animal tissue is heme iron. The iron in egg yolks, milk, and plant foods is all non-heme iron. Heme iron is generally better absorbed than non-heme iron.

Figure 17-3: Sources of heme and non-heme iron. Plants contain only non-heme iron.

Due to the “bloody-red” color of heme, we can correctly guess that red meat (e.g., beef) has more heme iron than light meat (e.g., chicken, fish), and that the darker meat of a chicken leg has more heme iron than the lighter meat of the chicken breast. Since heme-containing red blood cells are made in the bone marrow and broken down in the liver, bone marrow and liver are rich dietary sources of heme iron. (Bone marrow is eaten more commonly in Europe than in the U.S.).

Heme is a key ingredient in the vegan (plantbased) Impossible™ Burger that gives the burger its beef-like flavor and appearance. The gene (“recipe”) for heme is taken from DNA in the roots of soybean plants and then spliced into the DNA of yeast. These yeast are then used to produce the heme in large amounts. The heme ingredient is listed as leghemoglobin (soy); leg = legumes (e.g., soybeans). Vegan burgers are ecologically superior to beef (cows use a lot of water and land, and produce a lot of greenhouse gases), but are not necessarily nutritionally superior.

Non-Heme Iron

We eat lots of meat, but most of the iron in our diet is non-heme iron (as in fortified breakfast cereals and enriched bread).

Plant foods have non-heme iron, which is generally more poorly absorbed than heme iron. The absorption of non-heme iron can vary a lot (about 2% to 45%), depending on whether a person is deficient in iron, the amount of iron in the meal, and the composition of the meal. Thus, compared to heme iron, it’s hard to evaluate dietary sources of non-heme iron.

We can’t assume that a person will absorb more iron from a half-cup of cooked spinach (2 mg iron) at lunch than from an egg (1 mg iron) at breakfast, because other substances in the meals can affect the amount absorbed. For example, vitamin C-rich food, meat, or fish eaten at the same meal increases the absorption of non-heme iron.

Conversely, substances such as tannins (as in tea), phytic acid (as in wheat bran), and oxalic acid (as in spinach) in the meal can lower the amount absorbed by combining with non-heme iron, preventing its absorption.

We can expect to absorb more iron from an egg if the breakfast also includes sausage and a glass of orange juice, and less from a luncheon spinach salad served with a whole wheat roll and tea. Vitamin C in the orange juice and meat in the sausage increase absorption of the iron in the egg, whereas oxalic acid in the spinach, phytic acid in the whole wheat roll, and tannins in the tea all bind to iron and hamper its absorption.

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A spinach salad lunch may not be as good as an egg and sausage breakfast in terms of iron absorption, but it’s more in line with dietary advice to eat less saturated fat and more fiber.

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Because only a small amount of the iron ingested is actually absorbed, the recommended intake of iron is about ten-fold higher than what our bodies require. Adult men, for example, need about 1 mg/day, so their RDA is 8 mg/day.

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Foods rich in non-heme iron (have 1 to 2 mg iron):

• ¼ cup peanut butter, raisins, bran breakfast cereal;. or cooked cream of wheat
• ½ cup cooked spinach, chard, lima beans, or peas
• 2 slices enriched or whole wheat bread
• 1 egg yolk
• 3 dried apricot halves
• 5 prunes

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Milk and milk products make up a large part of children’s diets, and milk contains only a small amount of iron (about 0.1 mg of non-heme iron per cup). Newborns normally have about a 6-month’s supply of iron stored in the liver. This iron “holds them over” until other foods are added to their diet of milk. The iron in breast milk is better absorbed, so it’s recommended that infants less than a year old who aren’t being breast-fed exclusively, be given iron-fortified infant formula.

Iron Fortification and Supplements: The enrichment of flour with iron, and the fortification of many breakfast cereals with iron has reduced the incidence of iron-deficiency anemia in this country. Also, many people take iron supplements.

Iron supplements are generally inexpensive and readily available, but it’s still a good idea for those at risk of iron deficiency to work on improving their intake of iron-rich foods. Improving the diet in one nutrient—iron in this case—tends to improve the diet in other nutrients as well. Also, for some people, iron supplements can be constipating.

The form in which the iron is taken affects how well it’s absorbed. Its absorption is highest in such forms as ferrous (iron) sulfate, ascorbates, fumarates, and citrates. The latter three forms of iron are sometimes called chelates, and there is quite a lot of promotion for unreasonably expensive “chelated iron” supplements. (The same iron compounds are often available at much lower prices in grocery and drug stores.)

There’s also a simple way to supplement your diet with iron without pills. That is, by cooking acid-containing foods in old-fashioned utensils—cast iron pots and pans. If the food is somewhat acidic—containing a little vinegar, red wine, citrus juice, tomato juice, or almost anything that tastes rather sour—small amounts of iron will dissolve out of the pan and into the food. The iron content of tomato-based (acidic) spaghetti sauce, for instance, goes up when simmered in a castiron pot.

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An old folk remedy for anemia is to put a long iron nail in an apple overnight and then eat the apple—after removing the nail, of course.

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One can’t say precisely how much iron you’ll get from cast iron pots and pans, but it can be substantial. In fact, people have suffered from iron toxicity when iron vats have been used routinely to store or brew acidic drinks.

Iron Toxicity

Intestinal safeguards normally protect us from an excess of iron, but large amounts can overwhelm the system, and we can absorb too much. There have been many cases of acute and chronic iron toxicity where food or drink was accidentally heavily contaminated with iron.

An accidental overdose of iron supplements is the most common cause of acute iron poisoning in the U.S. The supplements usually belong to the child’s mother. Acute iron poisoning requires emergency treatment. Alcoholics and those with certain diseases (e.g., liver disease or thalassemia) are particularly vulnerable to iron toxicity.

Hemochromatosis

Because iron-deficiency anemia is common in this country, it’s been suggested that more staple foods be fortified with iron. The concern is that this might cause more cases of a disease called hemochromatosis. In this disease, excessive amounts of iron are absorbed from normal diets because of a genetic error that impairs the ability of the intestine to adjust iron absorption. The danger is an accumulation of iron to toxic levels in the body.

An estimated 1 out of 10 whites of Northern European ancestry in the U.S. has inherited the abnormal gene for hemochromatosis from one parent (heterozygotes), and about 1 in 2000 from both parents (homozygotes). It’s less common among those of Asian, Hispanic, and Native American ancestry.³

The genetic defect is distributed evenly among the sexes, but hemochromatosis is mainly a man’s disease. Men are at substantially greater risk because they can accumulate more iron over the years. Women, in contrast, “get rid of iron” in menstruation and pregnancy.

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Treatment for hemochromatosis includes extraction of blood (as in blood donations). As you’d expect, regular blood donors are at lower risk of hemochromatosis.

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Hemochromatosis rarely is discovered before middle age, presumably because it’s apparent only after many years of accumulating excess iron. Injury from the abnormal deposition of the excess iron occurs in various tissues, e.g., cirrhosis of the liver, and arthritis. It can be fatal. Early, mild, and vague symptoms of iron toxicity include joint pain and lack of energy.

Self-prescribed iron supplements taken by men and postmenopausal women are particularly worrisome in this regard. Also worrisome is regularly eating excessive amounts of iron-fortified breakfast cereal (the nothing-else-in-the-cupboard situation faced by many a college-age male).

Men and postmenopausal women generally don’t need iron supplements except, perhaps, if they’re regular blood donors. Even without a genetic defect for increased iron absorption, taking large doses of iron supplements might, over the years, put them at risk for iron toxicity. Men and postmenopausal women should avoid iron supplements and foods heavily fortified with iron, unless advised otherwise by a physician.