Agriculture Reference
In-Depth Information
ignorance of risk factors for specific micronutrient deficiencies•
ignorance and lack of reliable tests for status of specific micronutrients
inability to interpret such tests
lack of understanding of factors affecting supply and distribution of micro-
nutrients within the body
lack of understanding of needs and roles of micronutrients and how these
change with nutritional status and disease
reductive adaptation, by which nutrient deficiency limits growth and there-
fore nutrient requirements (World Health Organization 1999a)
The chapter is devoted mainly to a few micronutrient deficiencies for which we have
some knowledge and less understanding. Our knowledge comes from historical writ-
ings, geographic differences, scientific basic studies, and human intervention studies.
IRon
Iron, in humans, is the most abundant of the essential trace elements, comprising
around 5 g of an adult. It is mainly in hemoglobin in red blood cells. Iron deficiency
is purported to be the most prevalent of all deficiencies. This is because anemia, as
we define it, based on blood concentration of hemoglobin, is very common, espe-
cially in late infancy and pregnancy. Are our definitions of anemia correct? Are the
low hemoglobins all because of iron deficiency? We know the answer to the second
question is “No.” In large-scale studies in infants and young children, much of the
anemia was not associated with low iron stores (Duque et al. 2007).
Malaria is common and causes hemolytic anemia. Hemoglobin is not lost; its
iron is retrieved and reused. Thus, iron available for hemoglobin synthesis may be
adequate even though the anemia may be severe. Other infections are also associated
with a decrease in blood hemoglobin concentration without loss of iron.
Folic acid, vitamin B 12 , and vitamin A deficiencies (discussed separately) are rela-
tively common causes of anemia in young children.
In severely malnourished children, the red blood cell picture tends to be mixed,
showing signs of multiple deficiencies often compounded by malaria and other infec-
tions. Less-malnourished children comprise the vast majority of children living in
poverty. Their anemias tend also to be less severe but probably no less complex,
affected by multiple nutrient deficiencies and infections.
In pregnancy, hemodilution and major changes in nutrient transport and metabo-
lism occur; anemia is common even using a lower cutoff for hemoglobin concentra-
tion. Lactation is more clearly a drain on iron reserves.
Anemia in the elderly, as in malnourished children, tends to show a mixed pic-
ture, often with less evidence of iron than vitamin deficiencies.
Thus, all anemia is not due to iron deficiency but there is little doubt that it is com-
mon. Why? There is no shortage of iron in the Earth's crust. However, inorganic iron
and ferric salts are very poorly absorbed by humans. The form of iron that is most
bioavailable to us is that found in animal tissues, within heme. Most of the world's
children consume very little in the way of animal tissues. Most today have not been
exclusively breastfed—breast milk iron is also absorbed well. Iron in plants is mostly
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