The anemia that results from deficiencies of vitamin B12, folic acid (Chap. 9), or iron (Chap. 11) is, in general, clearly defined and is relatively common. In contrast, the characteristics of anemia that may occur with deficiencies of other micronutrients, including other vitamins and minerals, are poorly defined and relatively rare in humans. When present, they usually exist not as isolated deficiencies of one vitamin or one mineral but rather as a combination of deficiencies resulting from malnutrition or malabsorption. In this context, it is difficult to deduce which abnormalities are results of a particular deficiency. Studies in experimental animals may not accurately reflect the role of micronutrients in humans. Accordingly, our knowledge of the effect of many micronutrients on hematopoiesis is fragmentary and based on clinical observations and interpretations that may be flawed. Inborn metabolic errors that affect single micronutrient pathways may shed light on the specific effects of those micronutrients on hematopoiesis. The levels of relevant micronutrients normally found in the serum, red cell, and leukocytes are provided in this chapter.
Acronyms and Abbreviations:
EGRa, erythrocyte glutathione reductase activity; IBD, inflammatory bowel disease; IRIDA, iron-refractory iron-deficiency anemia; MCV, mean cell volume; MCHC, mean cell hemoglobin concentration; RDW, red cell distribution width; T3, triiodothyronine; T4, thyroxine.
Apart from iron, folate (vitamin B9), and cobalamin (vitamin B12), other trace mineral and vitamin micronutrients play an essential role in the prevention of anemia. Red cell numbers are adequately maintained by regulated continuous red cell production to counterbalance red cell loss due to the physiologic process of elimination of aged or damaged red cells from circulation or due to acute or chronic hemorrhage. Erythroid precursors in the marrow require adequate nutritional support to produce red cells to match the replacement of approximately 1% of the total red cell mass daily under steady-state conditions.
Deficiencies of other nutrients are not as common as folate, vitamin B12, and iron, but reports in the literature indicate that lack of other micronutrients can also lead to or exacerbate anemia. Leading examples of such nutrient deficiencies include protein-energy malnutrition, deficiencies of other B-group vitamins, riboflavin, pyridoxine and thiamine, ascorbic acid, the fat-soluble vitamins, A and E, and other trace elements such as copper, zinc, and selenium. Anemia caused by deficiencies of these micronutrients constitutes only a small fraction of the total burden of anemia accounted for by folate, vitamin B12, and iron deficiencies. Moreover, anemia resulting from vitamin B12, folic acid, or iron deficiencies is generally well defined and is relatively common; however, the characteristics of anemia arising from other micronutrient deficiencies are poorly defined and are infrequent in humans.
Miscellaneous micronutrient deficiencies can coexist, and it is often difficult to pinpoint which abnormalities are results of which nutrient deficiency. An ...