Iron deficiency anemia is a well-known and all-too-common problem, even with our modern knowledge about the condition and the attention given to preventing it. The preanemia state is not easy to diagnose. Decreasing iron stores and a relative decrease in serum iron levels and protein-bound iron may cause symptoms before low tissue iron levels or anemia are measurable. More of this important mineral is needed during growth; iron deficiency is more common in infancy, childhood, adolescence, and pregnancy. Even the elderly may become deficient due to poorer absorption and diet. Women in their reproductive years have a greater problem with iron deficiency because of losses in menstrual blood and higher requirements. Minority and low-income people tend to have a higher incidence of low iron-related problems, primarily caused by dietary deficiency. Women in their childbearing years require at least 18 mg. of iron daily, but more than 25 percent of them probably obtain less than this amount. Usually, when the body needs more iron, absorption improves through an increase in iron-carrying proteins in the blood, called iron transferrin.
Iron absorption from the intestinal tract is a very subtle process; poor absorption is one of the main reasons, along with low-iron diets, that iron deficiency is so prevalent. Along with calcium, which is also difficult to absorb, iron and zinc are the minerals most commonly deficient in our diet.
Average iron absorption is about 8-10 percent of intake. All vegetable sources contain the "nonheme" form of iron, which is poorly absorbed and utilized. "Heme" iron, a special formulation of iron, is found only in flesh foods, beef and liver being the best sources. Between 10 and 30 percent of heme iron is absorbed. Combining heme foods with nonheme foods improves the absorption of iron from the nonheme foods. This is why complete vegetarians have trouble obtaining sufficient iron from the diet alone. Phytates present in whole grains and oxalates found in certain vegetables may bind up some of the iron and make it unabsorbable. Meat foods improve absorption, possibly by stimulating increased stomach acid production and by the fact that the iron contained is already bound into muscle and blood tissue, the iron proteins myoglobin and hemoglobin.
Iron absorption is a slow process, usually taking between two and four hours. The food-natural ferrous (+2) ion is absorbed much better than iron in the ferric (+3) form. Vitamin C in the gut along with iron converts any ferric iron to ferrous and thus improves absorption. Iron absorbed into the blood is usually bound to the protein transferrin and goes mainly to the bone marrow, where it can be used to make red blood cells. Some also goes to the liver and spleen. About 25 percent of body iron is stored bound to the protein ferritin and as the iron complex hemosiderin. Ferritin has good iron-binding capacity. A fully saturated ferritin molecule, which is actually ferric oxide surrounded by the protein apoferritin, can contain about 4,000 iron atoms. Ferritin stored in the liver, spleen, and bone marrow, for example, provides a good reserve of iron to meet body needs. Measuring serum ferritin levels is a fairly new medical test that provides a good indication of iron storage levels. A normal value is 15-200 mcg. A level below 15 mcg. suggests very depleted iron reserves. Iron toxicity may show ferritin levels in the thousands.
About three-quarters of the iron in our bodies is active. Of that, about 70 percent is in hemoglobin, 5 percent is in myoglobin (muscle oxygenating protein), and the rest is part of iron cofactors and enzymes such as catalases, peroxidases, and the cytochromes. Some is also in transition, attached to transferrin, which transports iron to the bone marrow, liver, and other tissues for its functions in processing hemoglobin, myoglobin, and various enzymes. Fortunately, the body conserves iron very well, though this increases the possibility of toxicity. Toxicity has not been a great concern until recently, when the possibility of liver irritation and the increased risk of heart disease in men and postmenopausal women due to the oxidant effect of iron was suggested. About 1 percent of red blood cells are recycled each day (their average life span is 120 days), and we use the iron from them (about 30-50 mg. daily) to manufacture new cells. The recycled iron provides about 90 percent of the iron required to make new cells and to carry out other functions; therefore, we need only a little more for full functioning, unless, of course, there is blood loss.
Iron lost from the body must be replaced through dietary iron, but this often takes time and requires a regular source from food or supplements. A pint of blood contains about 200 mg. of iron. Even though iron absorption increases with increased need, it can still take several months to replenish the iron lost when we donate blood. About 30-40 mg. of iron will be lost during an average female menstrual cycle; this is why menstruating women need a consistently higher iron intake than men, a minimum of 18 mg. per day. During breast-feeding, the nursing mother will lose about 1-2 mg. per day. In pregnancy, the mother transfers 500-1000 mg. of iron to her growing baby, most of that (500-700 mg.) during the last few months. Since there are usually less than 500 mg. stored in the bone marrow and other tissues, the mother needs a regular, good dietary and supplemental intake of iron, or she will become very depleted and will be less able to obtain the extra oxygen she requires during pregnancy, labor, and delivery of her baby. After delivery, iron depletion could cause her to feel run-down and to have difficulty caring for her infant.
Many factors can increase iron absorption from the intestines and improve our chances of maintaining adequate body levels. Absorption improves when there is increased need for iron, as during growth periods, pregnancy, and lactation or after blood loss. Acids in the stomach, such as hydrochloric acid, and ascorbic acid (vitamin C) in the small intestine help change any ferric iron to the more easily absorbable ferrous form. Citrus fruits and many vegetables contain vitamin C and therefore help our iron absorption. The animal flesh foods have the more easily absorbed "heme," or blood, iron and also provide amino acids, which stimulate production of hydrochloric acid in the stomach. Cooking with an iron skillet will add iron to the food and make more of it available for absorption. Copper, cobalt, and manganese in the diet also improve iron absorption.
Likewise, many factors can reduce the body's iron absorption. Low stomach acid or taking antacids or other alkalis will diminish iron absorption. Rapid gastric motility reduces the chance to absorb iron, which is a slow process anyway. Phosphates, found in meats and soft drinks; oxalates, in spinach, chard, and other vegetables; and phytates, in the whole grains, all can form insoluble iron complexes or salts that will not be absorbed. Soy protein is being researched, as it may also reduce iron absorption. The caffeine and tannic acid in coffee and tea lower absorption of iron. Low copper in the gut and in the body reduces iron absorption, and high calcium can compete with iron. Supplementing calcium with iron may create a more alkaline digestive medium, which further reduces iron absorption. Iron absorption usually decreases with age as well.
Factors Affecting Iron Absorption
Increased by:
- Body needs during growth, pregnancy, and lactation
- Hydrochloric acid
- Vitamin C
- Blood loss or iron deficiency
- Meats (heme iron)
- Protein foods
- Citrus fruits and vegetables
- Iron cookware
- Copper, cobalt, manganese
Decreased by:
- Low hydrochloride acid
- Antacids
- Low copper
- Phosphates in meats and soft drinks
- Calcium
- Phytates in whole grains
- Oxylates in leafy green vegetables
- Soy protein
- Coffee and black tea
- Fast gastrointestinal motility
Any unabsorbed iron is eliminated in the feces. Otherwise, only minute amounts are lost in the urine, sweat, nail clippings, and hair. Other than through blood loss, most body iron is retained fairly well. Normal iron loss in the average person is about 1 mg. per day.
When we have plenty of iron, we can say we're "in the pink." Usually we will have good circulation, with rosy cheeks, pink earlobes, and pink tongue. (Yet we can also be "too pink" or red, with excess iron and blood cells.) If the tongue or the mucosal lining of the mouth is pale, we should look for anemia, so it is good for us to know what we can about iron, especially where we can find it in our foods.
Sources: Some of our soil is iron deficient, so the plants grown or the animals grazed there may contain relatively smaller amounts, though this is not yet a major concern. The milling of grain removes about 75 percent of the iron present in whole grains, as much of the iron is found in the outer bran and germ. The fortified or enriched grain foods, such as cereals and breads, contain some iron (plus vitamins B1, B2, and B3), but this iron is in the poorly absorbed ferric state. Cooking in iron pots or skillets will add absorbable iron to food, but if this is done excessively over time, iron toxicity is a possibility.
Heme iron, as found in meats, is generally thought to be the iron that is best absorbed, several times more absorbable than the nonheme iron found in the vegetable kingdom. This does not mean that we need to eat meats in order to get sufficient iron, though that is often recommended in cases of iron deficiency. The 18 mg. of iron a day needed by a woman in the childbearing years is not always easy to obtain through diet. Though eating 22 slices of whole wheat bread or 13 cups of cooked kale would supply 18 mg., these are obviously not desirable ways to get it. In addition to beef, liver, and other organ meats that have relatively high amounts of absorbable iron, pork, lamb, chicken, and shellfish such as clams and oysters contain reasonable iron levels. Egg yolks are fairly good sources, and salmon is the best of the other seafood.
From the vegetable world, whole grains are the overall best source. Wheat, millet, oats, and brown rice are all iron-containing grains. The legumes-dried peas and beans-are good; lima beans, soybeans, kidney beans, and green peas are examples. Nuts, such as almonds and Brazil nuts, and most seeds contain iron. Green leafy vegetables such as spinach, kale, and dandelion are good sources, as are broccoli and asparagus. Dried fruits such as prunes, raisins, and apricots have a good amount of iron. Prune juice often gives us additional iron. Unsulfured molasses is concentrated in iron; one tablespoon contains about 3 mg. Tomatoes, strawberries, and many other fruits and vegetables contain some iron, so it is possible to obtain adequate amounts of iron from dietary sources without consuming a lot of meat by eating wholesome foods, especially whole grains, green vegetables, and the legumes, nuts, and seeds.
Functions: The primary function of iron in the body is the formation of hemoglobin. Iron is the central core of the hemoglobin molecule, which is the essential oxygen-carrying component of the red blood cell (RBC). In combination with protein, iron is carried in the blood to the bone marrow, where, with the help of copper, it forms hemoglobin. The ferritin and transferrin proteins actually hold and transport the iron. Hemoglobin carries the oxygen molecules throughout the body. Red blood cells pick up oxygen from the lungs and distribute it to the rest of the tissues, all of which need oxygen to survive. Iron's ability to change back and forth between its ferrous and ferric forms allows it to hold and release oxygen. Each hemoglobin molecule can carry four oxygen molecules. This large protein molecule makes up approximately 30 percent of the RBCs. Amazingly, there are some 20 trillion RBCs in the average human body (men have more than women), and about 115 million red blood cells are made every minute. As mentioned before, approximately 90 percent of the iron needed to make those cells comes from recycled RBCs that are normally destroyed by the spleen at the end of their 120-day life span.