The availability of two B-complex vitamins—vitamin B12 and folic acid—significantly influences red blood cell production. These vitamins are required for DNA synthesis, so they are necessary for the growth and division of all cells. Since cell division occurs at a particularly high rate in hematopoietic tissue, this tissue is especially vulnerable to deficiency of either of these vitamins. Lack of vitamin B12 is usually due to a disorder in the stomach lining rather than to a dietary deficiency, because certain cells in the stomach secrete a substance called intrinsic factor that is needed for absorption of vitamin B12.
Iron is required for hemoglobin synthesis. Although much of the iron released during the decomposition of hemoglobin is available for reuse, some iron is lost each day and must be replaced. Only a small fraction of ingested iron is absorbed. Iron absorption is slow, although the rate varies with the total amount of iron in the body. When iron stores are low, absorption rate increases, and when the tissues are becoming saturated with iron, the rate greatly decreases. Figure 14.7 summarizes the life cycle of a red blood cell. The dietary factors that affect red blood cell production are summarized in table 14.3.
Vitamin C increases absorption of iron in the digestive tract. Drinking orange juice with a meal is a good way to boost iron intake.
A deficiency of red blood cells or a reduction in the amount of the hemoglobin they contain results in a condition called anemia. This reduces the oxygen-carrying capacity of the blood, and the affected person may appear pale and lack energy (fig. 14.8 and table 14.4). A pregnant woman may become anemic if she doesn't eat iron-rich foods, because her blood volume increases due to fluid retention to accommodate the requirements of the fetus. This increased blood volume decreases the hematocrit. Clinical Application 14.1 discusses another disorder of red blood cells that may have had an impact on American history.
In the absence of intrinsic factor, vitamin B12 absorption decreases, causing the red bone marrow to form abnormally large, irregularly shaped, thin-membraned fragile cells. This condition, called pernicious anemia, can cause permanent brain damage if not treated promptly with vitamin B12 injections. Taking excess folic acid — as pregnant women do to prevent neural tube defects in the fetus — can mask a vitamin B12 deficiency. These women must be careful to follow a balanced diet and get sufficient quantities of vitamin B12.
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