An Overview Of Common Causes Of Anemia

Anemia occurs when the concentration of the pigment hemoglobin in red blood cells falls below normal. Hemoglobin is essential for delivering oxygen from the lungs to the body tissues.

Iron deficiency is the most common cause of anemia. Although iron deficiency is generally the most common cause of anemia, there are other nutritional, genetic, and environmental causes as well.

Iron was one of the first substances identified as essential in the human diet. The physiologic function of iron in hemoglobin and its role in anemia was determined over a two hundred year period from the 1680's.

By World Health Organization criteria, anemia is considered to exist when the non-pregnant adult female has a haemoglobin level below 11 grams per 100 milliliter of venous blood.

Iron deficiency anaemia refers to anemia that results from iron deficiency or impaired iron status. Iron dependent physiologic functions can become impaired before anaemia develops. Although iron deficiency anemia can occur in all socioeconomic groups, it has historically been most common among the poor as is still the case today.

Causes of Anemia

Because the synthesis of blood cells requires many cellular and metabolic processes, a deficiency of any nutrient essential to hemoglobin production produces adverse effects on these processes. Good nutrition is fundamental to adequate red blood cell production. Nutritional anaemia may be due to a dietary deficiency of iron, folate, vitamin B12, protein, and other vitamins and minerals. Other causes of anemia include the inherited or acquired inability to use nutrients required for haemoglobin production.

Nutritional anaemia should be distinguished from deficiencies per se of iron, folate, or vitamin B12, because an individual may have manifest any one of these deficiencies without being anaemic. In iron deficiency disorders immune function and behaviour are not directly attributable to the anaemia. Similarly, the impaired nerve function of vitamin B12 deficiency occurs independently of anemia.

The bioavailability of iron is determined by the nature of the diet and by regulatory mechanisms in the digestion that reflect the body's physiologic need for iron. Two types of iron are present in food, heme iron and nonheme iron.

Most of the iron in the diet is present as nonheme iron and consists primarily of iron salts. The amount finally absorbed is influenced by other constituents of the diet that either enhance or inhibit, by decreasing solubility and the absorption of iron.

Iron absorption tends to be poor from meals in which whole grain products and legumes predominate, but the addition of even small amounts of foods containing vitamin C (ascorbic acid) substantially increase the absorption of iron from the entire meal. On the other hand, tea and coffee, decrease the absorption of nonheme iron.

Heme iron comes from the hemoglobin in meat, poultry, and fish. The body absorbs a greater percentage of heme iron, and its absorption is less affected by other dietary constituents.

Iron deficiency causes a substantial reduction in work capacity and mild anemia can decrease performance in exercise. The major consequence of this muscle impairment is a lessened capacity for prolonged exercise or physical endurance. An impaired capacity to maintain body temperature in a cold environment is another characteristic of iron deficiency anemia.

Changes in behaviour and impaired intellectual performance may result from iron deficiency. Even mild iron deficiency significantly decreases responsiveness, activity, and attentiveness, and increases body tension, fearfulness and a tendency to fatigue.

Iron deficiency and folate deficiency are more common in women because of two forms of metabolic stress peculiar to women; the monthly blood loss in premenopausal women and the drain on maternal nutrient stores imposed by pregnancy. The fetus will take from the mother whatever it needs in order to be normal at birth, even if this produces severe nutrient deficiency in the mother. Nevertheless, a women who has sufficient iron stores to provide for her increase in hemoglobin mass during pregnancy, and who breast-feeds for six months will have her iron needs covered by adequate intake of dietary iron.

Iron deficiency can be prevented by increasing dietary intake, improving bioavailability from the diet, or decreasing body losses of iron. Dietary intakes can be improved by increasing the consumption of iron-rich foods, administering iron supplements, and fortifying certain food products with iron. Fortification of cereal and grain products is a relatively inexpensive and effective means of increasing iron intake. The absorption of iron from fortified cereals can be increased threefold if the cereals are also fortified with about 5 mg of vitamin C per mg of iron.

Prevention of nutrition-related anaemia depends on adequate dietary intake of iron, vitamin B12, and folate as well as the full complement of other essential nutrients. Folate deficiency anemia usually occurs among women late in the course of pregnancy, among small premature infants, and among alcoholics. Strict vegetarians who consume no foods of animal origin, especially women who are pregnant or nursing, should take supplemental sources of vitamin B12.

Supplementation has the disadvantage of requiring extra effort and expense compared with fortified foods. Its effectiveness for a given individual requires evaluation by a qualified health professional. Iron supplement use and recommendations to increase dietary intake are usually not necessary for the general population.

An additional concern is that increased iron intake can harm individuals who are susceptible to iron overload. Abnormal amounts of tissue iron accumulate over the years as a result of a genetic defect in absorption, eventually damaging the liver, heart, pancreas, and adrenal glands. Excessive iron intake may affect the absorption of other trace elements.

Nutrition Programs and Services

Food Labels: Evidence related to the role of iron and folate in anemia suggests that food labels should indicate the content of these nutrients.

Food Programs: Because groups that benefit from food programs are those at highest risk for anemia, such programs should continue to be made available to high-risk groups and should encourage consumption of foods rich in iron and folate. The current levels of iron fortification are safe and adequate, and no changes should be recommended at this time.

  • The Surgeon General's Report on Nutrition & Health, 1988

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