Anemia can be caused by iron deficiency, folate deficiency, vitamin B12 deficiency, and other causes. The term iron deficiency anemia means anemia that is due to iron deficiency. Iron deficiency anemia is characterized by the production of small red blood cells. When examined under a microscope, the red blood cells also appear pale or light-colored. For this reason, the anemia that occurs with iron deficiency is also called hypochromic microcytic anemia.
Iron deficiency anemia is the most common type of anemia throughout the world. In the United States, iron deficiency anemia occurs to a lesser extent than in developing countries because of the higher consumption of red meat and the practice of food fortification (addition of iron to foods by the manufacturer). Anemia in the United States is caused by a variety of sources, including excessive losses of iron in menstrual fluid and excessive bleeding in the gastrointestinal tract. In developing countries located in tropical climates, the most common cause of iron deficiency anemia is infestation with hookworm.
Causes and symptoms
Infancy is a period of increased risk for iron deficiency. The human infant is born with a built-in supply of iron, which can be tapped during periods of drinking low-iron milk or formula. Both human milk and cow milk contain rather low levels of iron (0.5–1.0 mg iron/liter). However, the iron in human milk is about 50% absorbed by the infant, while the iron of cow milk is only 10% absorbed. During the first six months of life, growth of the infant is made possible by the milk in the diet and by the infant's built-in supply. However, premature infants have a lower supply of iron and, for this reason, it is recommended that preterm infants (beginning at two months of age) be given oral supplements of 7 mg iron/day, as ferrous sulfate. Iron deficiency can be provoked where infants are fed formulas that are based on unfortified cow milk. For example, unfortified cow milk is given free of charge to mothers in Chile. This practice has the fortunate result of preventing general malnutrition, but the unfortunate result of allowing the development of mild iron deficiency.
The normal rate of blood loss in the feces is 0.5–1.0 ml per day. These losses can increase with colorectal cancer. About 60% of colorectal cancers result in further blood losses, where the extent of blood loss is 2–10 ml/day. Cancer of the colon and rectum can provoke losses of blood, resulting in iron deficiency anemia. The fecal blood test is widely used to screen for the presence of cancer of the colon or rectum. In the absence of testing, colorectal cancer may be first detected because of the resulting iron deficiency anemia.
Infestation with hookworm can provoke iron deficiency and iron deficiency anemia. The hookworm is a parasitic worm. It thrives in warm climates, including the southern United States. The hookworm enters the body through the skin, through the soles of bare feet. The hookworm then migrates to the small intestines where it attaches itself to the villi (small sausage-shaped structures in the intestines that are used for the absorption of all nutrients). The hookworm damages the villi, resulting in blood loss, and they produce anti-coagulants that promote continued bleeding. Each worm can provoke the loss of up to 0.25 ml of blood per day.
The symptoms of iron deficiency anemia include weakness and fatigue. These symptoms result from dys-function of the red blood cells, and the reduced ability of the red blood cells to carry iron to exercising muscles. Iron deficiency can also affect other tissues, including the tongue and fingernails. Prolonged iron deficiency can result in changes of the tongue, and it may become smooth, shiny, and reddened. This condition is called glossitis. The fingernails may grow abnormally, and acquire a spoon-shaped appearance.
Decreased iron intake is a contributing factor in iron deficiency and iron deficiency anemia. The iron content of cabbage, for example, is about 1.6 mg/kg food, while those of spinach (33 mg/kg), lima beans (15 mg/kg), potato (14 mg/kg), tomato (3 mg/kg), apples (1.5 mg/kg), raisins (20 mg/kg), whole wheat bread (43 mg/kg), eggs (20 mg/kg), canned tuna (13 mg/kg), chicken (11 mg/kg), beef (28 mg/kg), corn oil (0.6 mg/kg), and peanut butter(6.0 mg/kg), are indicated. One can see that apples, tomatoes, and vegetable oil are relatively low in iron, while whole wheat bread and beef are relatively high in iron. The assessment of whether a food is low or high in iron can also be made by comparing the amount of that food eaten per day with the recommended dietary allowance (RDA) for iron. The RDA for iron for the adult male is 10 mg/day, while that for the adult woman is 15 mg/day. The RDA during pregnancy is 30 mg/day. The RDA for infants of 0–0.5 years of age is 6 mg/day, while that for infants of 0.5–1.0 years of age is 10 mg/day. The RDA values are based on the assumption that the consumer eats a mixture of plant and animal foods.
The above list of iron values alone may be deceptive, since the availability of iron in fruits, vegetables, and grains is very low, while the availability from meat is much higher. The availability of iron in plants ranges from only 1–10%, while that in meat, fish, chicken, and liver is 20–30%. The term availability means the percent of dietary iron that is absorbed via the gastrointestinal tract to the bloodstream. Non-absorbed iron is lost in the feces.
Interactions between various foods can influence the absorption of dietary iron. Vitamin C can increase the absorption of dietary iron. Orange juice is a rich source of vitamin C. Thus, if a plant food, such as rice, is consumed with orange juice, then the orange juice can enhance the absorption of the iron in the rice. Vitamin C is also added to infant formulas, and the increased use of formulas fortified with both iron and vitamin C have led to a marked decline in anemia in infants and young children in the United States (Dallman, 1989). In contrast, if rice is consumed with tea, certain chemicals in the tea (tannins) can reduce the absorption of the iron. Phytic acid is a chemical that naturally occurs in legumes, cereals, and nuts. Phytic acid, which can account for 1–5% of the weight of these foods, is a potent inhibitor of iron absorption. The increased availability of the iron in meat products is partly due to the fact that heme-iron is absorbed to a greater extent than free iron salts, and to a greater extent than iron in the phytic acid/iron complex. Nearly all of the iron in plants is nonheme-iron. Much of the iron in meat is nonheme-iron as well. The nonheme-iron in meat, fish, chicken and liver may be about 20% available. The heme-iron of meat may be close to 30% available. The most available source of iron is human milk (50% availability).
Tom Brody PhD, The Gale Group Inc., Gale, Detroit,